US 20150042793A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2015/0042793 A1 (43) Pub. Date: Belenkii et al. (54) CELESTIAL COMPASS WITH SKY POLARIZATION (52) vs. C]. CPC ............. .. @010 21/02 (2013.01); G01S 3/7864 (2013.01); G01S 3/7861 (2013.01); G01S 3/7867 (2013.01) (71) ApplicantszMikhail Belenkii, San Diego, CA (US); Lawrence Sverdrup, Poway, CA (US); Vladimir Kolinko, San Diego, CA (US) (72) Inventors: Mikhail Belenkii, San Diego, CA (US); Lawrence Sverdrup, Poway, CA (US); Vladimir Kolinko, San Diego, CA (US) Feb. 12, 2015 USPC (57) ........................................................ .. 348/143 ABSTRACT A celestial compass With a sky polarization feature. The celestial compass includes an inclinometer, a camera system (73) Assignee: TreX Enterprises Corporation (21) Appl. No.: 13/987,604 Aug. 12, 2013 (22) Filed: Publication Classi?cation for imaging at least one celestial object and a processor pro grammed With a celestial catalog providing known positions at speci?c times of at least one celestial object and algorithms for automatically calculating target direction information based on the inclination of the system as measured by the inclinometer and the known positions of at least one celestial object as provided by the celestial catalog and as imaged by (51) Int. Cl. G01 C 21/02 G01S 3/786 (2006.01) (2006.01) 0%, the camera. Preferred embodiments include backup compo nents to determine direction based on the polarization of the sky when celestial objects are not visible. Patent Application Publication Feb. 12, 2015 Sheet 1 0f9 US 2015/0042793 A1 FIG. 1 11? ///J 7% Patent Application Publication Feb. 12, 2015 Sheet 2 0f9 US 2015/0042793 A1 M.8a5gn7u5m . m.UE M9NHE.NNaRwDGN:EM- .i g. @M0Ocm2Z0uHm Patent Application Publication [email protected] Feb. 12, 2015 Sheet 3 0f9 US 2015/0042793 A1 [email protected] UE%[email protected]$EQ§ QCWMwZSQuUm Patent Application Publication UNHFZWnAJMEH US 2015/0042793 A1 Feb. 12, 2015 Sheet 4 0f 9 UHEMeZ5<6A~m>H0 mE.a2g13n5um 0 O, i, ® o Awwmwwe w. w/@ 1NMH AHQ \[email protected] .Umhm A/ Patent Application Publication Feb. 12, 2015 Sheet 5 0f 9 1 s 4 5 US 2015/0042793 A1 6 7 z 44 43 46 Q 42 ‘ , , , 52 *///////////////// / .//_ F .Z'f-j 50 \“\-\ ""1151 r/ ',‘““4’ . ~ '__ 7" \§$'\ - I j '/ , 7 V I ' \x. ~ _ 56 FIG. 7 Patent Application Publication Feb. 12, 2015 Sheet 8 0f 9 ‘1..-... Fm w US 2015/0042793 A1 Patent Application Publication Feb. 12, 2015 Sheet 9 0f 9 Histograms: AOP Difference 6000 F(rpelqxunscy) 4000 2000 Angle (deg) FIG. 11 US 2015/0042793 A1 Feb. 12, 2015 US 2015/0042793 A1 CELESTIAL COMPASS WITH SKY POLARIZATION better than 2 milliradians are available from suppliers such as CROSS REFERENCE TO RELATED APPLICATIONS Jewell Instruments with of?ces in Manchester, NH. and Digikey with of?ces in Thief River Falls Minn. The cost of these inclinometers typically is in the range of about $60.  This application is a continuation in part of patent applications Ser. No. 13/373,009 ?led Nov. 1, 2011 which Digital Magnetic Compasses eters (such as Analog Devices ADIS 162097) with accuracies was a CIP of Ser. No. 12/ 283,785, Portable Celestial Compass  ?led Sep. 15, 2008, Ser. No. 12/319,651, Angles Only Navi one degree, and the presence of steel or other local distur gation System ?led Jan. 8, 2008 and Ser. No. 12/583,776 Miniature Celestial Direction Detector ?led Aug. 25, 2009 and Ser. No. 12 586,813 ?led Sep. 28, 2009, each ofwhich are bances will often reduce accuracy of the magnetic compasses to several degrees or render them useless. Therefore, if posi Magnetic compasses are typically accurate to only incorporated herein by reference. This application also claims tioning of a target depends on the use of a magnetic compass, substantial position errors could likely result. In the case of the bene?t of Provisional Application Ser. No. 61/742,448, ?led Aug. 10, 2013. military operations, the accuracy of current and future ?re support systems strongly depends on the errors in target coor FEDERAL SUPPORTED RESEARCH eral damage and improve target lethality, a target locator error  The present invention was made in the course of work under Marine Corps contract number M67854-12-C 6501 and the United States Government had rights in the invention. on the order, of less than, 10 meters at 5 km range is needed. Current target location technology does not meet this stan dard. The main source of error is magnetic compasses. Com dinates called target location error. In order to reduce collat FIELD OF INVENTION  The present invention relates to direction detection systems, especially to such systems designed for use in deter mination of precise locations of targets. BACKGROUND OF THE INVENTION Sky Charts  The position of celestial objects at any time at any place on earth is known with extremely high accuracy. These celestial objects include all recognizable stars andplanets, the monly a ground-based observer determines target coordi nates using a laser range?nder, GPS receiver, and magnetic compass. Under ideal magnetic conditions the measurement error (usually referred to as an “RMS error” of a magnetic compass is typically 10-17 milliradians. This corresponds to the locator error of 50-85 meters at a 5 km range. In many situations knowledge of the true aZimuth to a target with precision of much better than 1 degree (about 17.45 millira dians) is needed. Also magnetic compasses are highly sensi tive to random errors caused by weakly magnetic distur bances (e.g. vehicles, buildings, power lines etc.) and local variations in the earth’s geo-magnetic ?eld. These error sources are random and cannot be accurately calibrated and modeled to subtract out. A large magnetic disturbance from sun and the moon. Celestial objects also include visible man hard or soft iron effects can result in target accuracy errors of made satellites. Accurate positioning of the celestial objects depends only on knowledge of the latitude and longitude up to 30 to 60 degrees. Attitude Heading and Reference Systems positions and on the date and the time to within about 1 to 3 seconds of observation. Latitude and longitude generally can be determined easily with precision of less than one meter with global positioning equipment. Computer programs with astronomical algorithms are available that can be used to calculate the positions of any of these celestial objects at any  Attitude heading reference systems (AHRSs) are 3-axis sensors that provide heading, attitude and yaw infor mation for aircraft and other systems and components. AHRSs are designed to replace traditional mechanical gyro time for any position on or near the surface of the earth. Star scopic ?ight instruments and provide superior reliability and pattern recognition computer programs are available in the prior art. These computer programs are described in several accuracy. These systems consist of either solid-state or MEMS gyroscopes, accelerometers and magnetometers on all three axes. Some of these systems use GPS receivers to good text books including Astronomical Algorithms by Jean Meeus, published by Willmann-Bell with of?ces in Rich mondVa. Techniques for using the programs to determine the positions of the celestial objects are clearly described in this reference. Programs such as these are used to provide plan improve long-term stability of the gyroscopes. A Kalman ?lter is typically used to compute solutions from these mul tiple sources. AHRSs differ from traditional inertial naviga etarium programs such as “The Sky” available from Software tion systems (INSs) by attempting to estimate only attitude (e.g. pitch, roll) states, rather than attitude, position and Bisque and “Guide” available from Project Pluto. velocity as is the case with an INS.  AHRSs have proven themselves to be highly reli Fisheye Lenses able and are in common use in commercial and business  Fisheye lenses are lenses with a highly curved pro truding front that enables it to cover a solid angle of about 180 degrees. The lenses provide a circular image with barrel dis tortion. brought the price of Federal AviationAdministration certi?ed MEMS Inclinometers  Vertical at the observation position can easily be found by using an inclinometer. Tiny MEMS type inclinom aircraft. Recent advances in MEMS manufacturing have AHRS’s down to below $15,000.  Although gyroscopes are used to measure changes in orientation, without the absolute references from acceler ometers and magnetometers the system accuracy quickly degrades. As such, when there are extended periods of inter ferences or errors introduced into the sensing of gravity or magnetic ?eld performance of the system can be seriously Feb. 12, 2015 US 2015/0042793 A1 compromised. As a general reference, gravity is almost per Standards and published in the Review of Scienti?c Instru fectiit is a constant force that is not in?uenced dramatically ments in 1949. The accuracy was estimated to be approxi by anything. The most dif?cult error introduced in sensing gravity is the acceleration added during movements. Each time the system or component is moved, acceleration is sensed, thus creating a potential for error. This however is mately 1°, decreasing if the zenith is obscured by clouds. easily mitigated by applying algorithms to the data that ?lter out such high frequency accelerations, resulting in a very accurate means of determining the vector of gravity. Note that this information is used only for initial setup and system corrections, and is not needed for real-time tracking of orien The Need  What is needed is a non-magnetic compass that can operate day and night, and in most weather conditions, and does not require an un-obscured line of sight to the sun or moon. SUMMARY OF THE INVENTION tation. Magnetic ?eld disturbances are much more di?icult to deal with.  The present invention provides a celestial compass including a sky polarization feature. The celestial compass Sky Polarization  It is known that in general the sky light is polarized includes an inclinometer, a camera system for imaging at least one celestial object and a processor programmed with a celes tangential to a circle centered in the sun and maximum polar ization is found at ninety degrees from the circle. Therefore, with the sun close to the zenith the sky light will be polarized horizontally along the entire horizon. On the other hand, when the sun is setting in the West, the sky will be maximally polarized along the meridian and thus vertically at the due North and South. Toward the zenith just after sunset (or before sunrise) the degree of polarization of the sky light can reach its maximum of about 75 percent on very clear days,  Numerous creatures utilize the sky polarization compass for navigation, with new examples being continu ally discovered. Desert ants cannot leave a pheromone trail because this biochemical signal is subject to evaporation. Instead they use a sky polarization compass.i Bees also use a tial catalog providing known positions at speci?c times of at least one celestial object and algorithms for automatically calculating target direction information based on the inclina tion of the system as measured by the inclinometer and the known positions of at least one celestial object as provided by the celestial catalog and as imaged by the camera. Preferred embodiments include backup components to determine direction based on the polarization of the sky when celestial objects are not visible.  In referred embodiments the camera system includes a telecentric ?sheye lens that produces an image on the sensor located at or near the focal plane which remains spatially constant within sub-micron accuracies despite ther mally produced changes in the focus of the lens. These sky polarization compass. Migratory birds utilize the earth’s embodiments may also include a movable ?lter unit to magnetic ?eld, the stars and the sun as compasses, but the sky polarization compass is utilized to calibrate all of the other compasses. Dung beetles have been shown to use a sky polar ments the ?lter unit includes an electromagnetic switch. In ization compass at night where sky illumination is provided increase greatly the dynamic range of the kit and permit day and night operation with the single lens. In preferred embodi other embodiments the switch is a manual switch or a motor driven switch. The ?lter in preferred embodiments is com by the moon. The ability to use polarization vision in the animal kingdom is probably much more widespread than we realize.  It is known that some animals use green light, many use blue light, but most use near ultraviolet light for their sky polarization compass. The reason for this is apparently that in permits imaging of the moon and sun through light cloud adverse conditions such as complete overcast, the sky polar ization signal is largest in the UV. In clear conditions, it is navigation sensor including a magnetic compass and a largest in the blue/green spectral region.  The ?rst known sky polarization compass was built in the 1940’s as a single pixel device measuring the sky at zenith. It has been reported that the Scandinavian airlines SAS used a “single-zenith-pixel” sky polarization compass during polar ?ights in the 1950’s. In the late 1990s a Swiss group mimicked desert ant navigation, building a robot that navigated using a single zenith pixel sky polarization com pass.  A device known variously as the Pfund compass, the Kollsman Sky Compass, or simply as the “twilight” compass, was utilized by the US Navy in 1948. It determined the prised of a thin Mylar ?lm coated with a special partially re?ective coating. With the increased dynamic range of the camera the moon can be imaged during the period after sunset and before sunrise when stars are not visible. The compass cover. Other preferred embodiments can include an inertial memory-based optical navigation system that permits contin ued operation on cloudy days and even in certain in-door environments. In some preferred embodiments calibration components may be provided in a separate module to mini mize the size and weight of the compass.  These embodiments use celestial sighting of the sun, moon or stars to provide ab solute azimuth measurements relative to ab solute north. In preferred embodiments the incli nometer is an internal MEMS inclinometer providing mea surements relative to the local vertical (gravity based). Celes tial observations are combined with known observer position and time, which can normally be obtained from a GPS azimuth of the sun when the sun was not visible by examining receiver, in order to compute the absolute azimuth pointing of the polarization of the sky at zenith. This proved to be extremely valuable in the far north, where magnetic com passes are minimally useful, and twilight conditions can per advantages over the similar prior art device discussed in the sist for long durations, during which both sun and stars are not visible and therefore useful for navigation. The accuracy was reported to be about 0.50.  A version of a sky polarization compass that utilized sky light at zenith was developed at the National Bureau of the device.  The present invention has the following principal background section:  Nonmagnetic compass  No performance degradation over time (no drift)  Compact  No moving parts (other than the ?lter) Feb. 12, 2015 US 2015/0042793 A1  Lightweight for imaging the sun during daytime and for imaging the moon   Low power Low cost  RMS azimuth measurement error is about 1 mil and stars during the nighttime. Since brightness levels during the day are many orders of magnitude greater during the day as compared to night, applicants have designed an automatic  Low production cost  Allow for operation in urban environments, near vehicles and power lines, and while wearing body armor  Near zero startup time (azimuth measurement in about 2 seconds) BRIEF DESCRIPTION OF THE DRAWINGS  FIG. 1 illustrates a preferred embodiment of the present invention where the celestial compass is an accessory of a far target location (FTL) system.  FIG. 2 is a prospective view of a preferred embodi ment of the present invention.  FIG. 3 is a cross sectional drawing showing features of the FIG. 2 embodiment.  FIG. 4 is an exploded view drawing of the FIG. 2 embodiment.  FIG. 5 is a breakaway drawing of the electronic ?lter mechanism of the preferred embodiment.  FIG. 6 is a drawing showing the lens elements of a telecentric ?sheye lens specially designed for this preferred embodiment of the present invention.  FIG. 7 is a cross sectional drawing ofa portion ofthe ?sheye lens showing detailed features of the lens.  FIG. 8 is a block diagram showing electronic com ponents of the above preferred embodiment of the present invention.  FIG. 9 is a set of speci?cations for the telecentric ?sheye lens system.  FIG. 10 shows an experimental setup for testing sky polarization components.  FIG. 11 shows test results of the sky polarization shutter-?lter system permitting the same lens-sensor unit to be used during the day and at night. The preferred shutter unit is shown at 20 in the FIG. 3 drawing. The shutter blade is shown at 22, the ?lter is shown at 24 and the CMOS sensor is shown at 26. The CMOS sensor is a 5 mega pixel CMOS sensor Model No. MT9P031 provided by Aptina with of?ces in San Jose, Calif. FIG. 4, which is an exploded view drawing, shows additional details of the celestial compass including lens assembly 14, lens mount 30, shutter unit 20 and shutter permanent magnetic cover 32. Under the cover (not shown is an electric magnet in the form of a circularly-shaped coil. The CMOS sensor is shown at 26. These components are mounted on circuit board 16. Shutter-Filter  The shutter-?lter is a modi?ed version of an off-the shelf shutter available from Uniblitz with of?ces in Osborne, Wash. The shutter was converted to an “in or out” ?lter. This shutter-?lter includes a small permanent magnet shown at 32 in FIG. 5 that is positioned within a break in the circularly shaped coil of the electro magnet. The direction of current ?ow through the coil of the electromagnet determines the position of ?lter blade 24. A reversal of current in the coil changes the orientation of the magnet and the shutter blade by 180 degrees. Current ?ow in a ?rst direction orients the ?lter above CMOS sensor 26 for imaging the sun during daytime operation of the celestial compass and current ?ow in the opposite direction orients the ?lter away from the sensor for nighttime operation for imaging the moon or stars. The ?lter blade is held in place by friction if no current is ?owing in the coil. So current is required only when changing the ?lter position. The ?lter itself is a thin ?lm ?lter on a polyester tests. (preferably Mylar®) substrate providing 106 blocking. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Telecentric Lens First Preferred Embodiment  FIGS. 6 and 7 are drawings of telecentric ?sheye lens utilized in the preferred embodiment of the present  A ?rst preferred embodiment of the present inven tion can be described by reference to FIGS. 1 through 9. FIG. 1 shows a celestial compass as a component of a far away target location system mounted on a tripod. The celestial compass has imaged the sun and with information from an invention. The lens unit consists of seven optical elements shown as elements 1 through 7 in FIG. 6. The mechanical details of the layout are shown in the cross sectin drawing of FIG. 7. It consists of a single lens tube with a varying diam eter. The inner diameter of the tube at each axial position matches the diameter of the lens elements and spacers that it inclinometer (not shown), the correct date and time and the correct geographic position of the laser ?nder, the processor within the celestial compass has determined the orientation of a telescope in the far target location system and with the timing of a return infrared laser pulse from target has deter mined the exact geographic position of the target.  A preferred module of the celestial compass of the present invention is shown in detail in FIGS. 2 through 8. FIG. threaded retainer ring 48 for holding lens element 2, several holes 52 in lens mount 42 for permitting injection of adhesive 2 is a prospective view of the celestial compass. Shown in the to ?x lens elements 3-7 and their associated spacers, spaceri drawings is celestial compass, with a single ?sheye lens optical stop 54 hole 46 for adhesive for ?xing lens element 1 and spacer 56 for setting the space between lens elements 6 assembly 14 mounted on circuit board 16. Also shown is inclinometer unit 18 which is an off-the-shelf unit, Model ADIS 16209 furnished by Analog Devices with of?ces in Norwood Mass.  FIG. 3 is a cross sectional drawing showing some contains. An integral skirt is part of the lens mounting struc ture and is used to attach the lens to an outer structure. Shown in FIG. 7 are lens mount structure 42 to hold the lens ele ments, a threaded retained ring 44 for holding lens element 1 and to preload in compression all subsequent lens elements, a and 7. Two sets of cemented doublets are constructed using lens elements 3&4 and 5&6 as shown in FIGS. 6 and 7. The additional features of this preferred embodiment. This celes speci?cations for the optical elements are found in the table in FIG. 9. Lens element 1 is held in place with retaining ring 44 which compresses the element against a ledge in the lens tial compass utilizes a single lens and a single CMOS sensor mount. In order to insure mechanical stability each element of Feb. 12, 2015 US 2015/0042793 Al  the lens and each spacer is attached to the lens tube by way of temperature volcanizing (RTV) silicone. For elements 1 and 2 the adhesive is applied in a 360° ring around the lens element. For elements 3-7 and the spacers around these ele ments as pictured in FIG. 7. The lens mount structure 42 has a series of holes 52 in it by which the adhesive may be injected as described above. The process of delivering the adhesive should insure that the adhesive contacts the side of the lens element or spacer that is radially in line with, and ?ll the entire  4) Determine azimuth offset by taking difference between measured azimuth (step 3) and known sun posi tion (from time and position).  5) Mathematically rotate boresight pointing in inclinometer coordinates to local horizon coordinates (with unknown azimuth) using inclinometer measure ments hole. Four adhesive holes are distributed at 90° increments at  each axial hole position. In order to facilitate applying the adhesive into the holes in the lens tube corresponding holes are position radially in the skirt structure. These allow a hollow adhesive dispensing tube to access the inner holes. To insure stability over a wide temperature range the housing structure, retaining rings, and lens spacers are made of tita nium. Electronic Components  FIG. 8 is a block diagram showing important fea tures of the electronic components of the above preferred embodiment of the present invention. These components include a set of voltage regulators 60 supplied by and external 5 volt source 62 and an external interface connector 64 in communication with digital signal processor 66 which is a 3) Mathematically rotate azimuth and zenith from inclinometer frame to local horizon frame with unknown azimuth offset. an adhesive. The preferred adhesive is a non-outgassing room 6) Determine absolute azimuth of boresight by azimuth offset determined in step (4).  Calibration procedure: Reverse steps (5) and (6) above while siting targets with known absolute azimuth. The calibration procedure and the procedure for absolute target azimuth and zenith (elevation) angle determination is described below.  A brief description of variable notation is summa rized in Table 2. The reader should note that all coordinate rotations are based on small angle approximations. This seems reasonable since all measurements of the optical axis offset from the inclinometer z-axis (zenith pointing for zero readings) show angles less than 10 milliradians. All measure ments were based on objects with inclinometer pitch and roll readings less than 5 degrees. Devices with of?ces in Norwood, Mass. The processor is  The sun position on the sensor is determined by a center of mass calculation. A matched ?lter determines the programmed and de-bugged with JTAG interface 68. The location of the sun (not necessary simply ?nding the peak is DSP module (Model Back?n 537) supplied by Analog output of DSP 66 is an input to an Ethernet PHY chip 70 suf?cient). The background (+camera analog to digital bias) (Model KS8721BLI) supplied by Micrel Inc. with of?ces in San Jose, Calif. and a 20 pin connector 72 which provides for is determined as the average of a 32x32 pixel region centered on the peak and excluding the center 16x16 pixels. A center of a connection with a simulator an a image display monitor (not mass calculation is made including only those pixels in the shown). The DPS module 66 is also in communication with 16x16 region with signal exceeding 5% of the peak value. CMOS sensor 26 via an 12C level shifter 73 and a 12 bit Data Bus as shown in FIG. 8. And the module 66 is also in com the optical axis on the sensor is a linear function of the zenith munication with shutter controller 74 and inclinometer 18 through an 8 Bit l/O expander as shown in the drawing. The inclinometer is a small high accuracy, dual-axis digital incli  The equations assume that the image distance from angle under the following additional assumptions:  1) lnclinometer axes are orthogonal. (Presumably determined by lithography/etch on MEMS since both nometer and accelerometer Model ADIS 16209 supplied by Analog Devices with of?ces in Norwood, Mass. axes were on a single die).  2) Row/ column axes combined with ?sheye bore sight constitute an orthogonal coordinate system. Process for Converting Celestial Data Into Target Direction TABLE 2  To determine the accurate location of a small celes tial target relative to the camera requires only a centroid measurement. To determine the accurate celestial location of the sun or moon requires ?nding the edges of the target and then calculating the true center based on the size and shape of the target at the time of the observation. The software as indicated above must correct for the distortion of the ?sheye Parameter De?nitions (1) (x50, yso) = array center in pixels on sensor (2) Ax = angular pixel size (3) (ax, [55) pitch and roll of ?sheye optical axis with respect to inclinometer z—axis (zenith for leveled inclinometer) (4)17, 61,) = azimuth and zenith angle ofbinocular boresight (4) in inclinometer reference frame. lens while also converting image data into astronomical coor dinates, preferably elevation, bank and azimuth.  Outline of basic daytime algorithm processing steps:  1) Measure sun azimuth and zenith on the ?sheye where radius to center is proportional to the zenith angle and azimuth is the angle between column offset and row offset from the center.  2) Mathematically rotate azimuth and zenith angle (small angle approximation) from sensor/?sheye frame to inclinometer frame (i.e. calibrate by determin ing ?sheye boresight when inclinometer is zeroed). Measured Quantities (1) (x5, ys) = sun centroid on sensor (2) (6%, 6y) = inclinometer measured pitch and roll. (1) (4):, 65) = measured sun azimuth and zenith angle in Calculated Quantities sensor/?sheye frame (2) (3) (4) (4)0, 60) = measured sun azimuth and zenith angle in inclinometer frame ((1),, 6,) = measured sun azimuth and zenith angle in module based local horizon coordinates A¢SM = yaw of module based local horizon coordinates relative to true local horizon coordinates (ENU). Feb. 12, 2015 US 2015/0042793 A1 TABLE 2-continued cos 0 Parameter De?nitions (5) sin 0' ¢,' = absolute azimuth of the sun in local horizon coordinates (ENU) calculated based on solar ephemeris, (6) time, and geo—location The slope of a linear least squares ?t provides the axis pitch ¢b,' = absolute azimuth of the target Detailed equations are set forth below: (or roll), and the intercept provides the offset in center column Coordinate system for sun position analysis. (1) (2) Measure sun centroid (x5, yS) Azimuth and zenith angles in sensor coordinates (or row). Error Analysis  The following is an error analysis. It is based directly on the coordinate transformation equations detailed above, so it cannot be considered an independent check. The 0, = AX (3) (x. — sz + (Y. — no? results are based on small value approximations. As a ?rst approximation two axis values which add in quadrature phase (a cos x+b sin x) are simply combined in a single “average” Rotate to optical axis 4%. = ¢. + (6. sin ¢. + (1. cos ¢.> cot 6. 90 = 9. + H5. COS (I). + (1. sin (PS) (4) term, and systematic errors (such as errors in determining the Rotate to local horizon using inclinometer measurements, (6%, 6y) calibration parameters) are treated in the same manner as 4), = (1)0 — (6y sin (1)0 — 6X cos (1)0) cot 60 random errors (centroid measurement error, mechanical drift, q» = 4%. + (By cos ¢.. + 6.. sin qt.) inclinometer noise, etc). M... = M - 4» Where 4); is the absolute azimuth of the sun. (5) Rotate boresight to local horizon coordinates (Pb! = (Pb - (9y Sin (Pb - 9); 005 (Pb) mt 9b 61,, = 61, + (By cos 4), + 6X sin 4);) (PMy = $171+ A¢SMYI Where ¢bl' is the absolute azimuth of the target, and 6b, is the  An attempt is made to maintain consistent notation with the explanation of the coordinate transformation. For the simpli?ed case with the inclinometer level, the variance in determining absolute azimuth is approximately: absolute zenith angle of the target. 2 2 01%, zo'wb +le 1 2 ES 2 +(Sin2 as 10'; + Calibration Procedures  Several calibration parameters must be determined experimentally. They are listed as the ?rst set of items (1) through (4) in Table 2. Based on small angle approximations the systematic error in measured azimuth resulting from errors in the array center point and off zenith ?sheye boresight  A brief summary of the terms is listed in Table 3. TABLE 3 is given by: Summary of error contributions for leveled operation. (1) 0% = error in boresight azimuth calibration cos OS A06 sin OS 0, (2) 0w = error in calculated sun location in ENU frame. Time, geo—location, and ephemeris errors are all believed to be negligible. Error for (3) as = average of ?sheye boresight angular offset from inclinometer z—axis where Aq) is the error in the azimuth measurement, ((1)6, A66) (4) 0,65 = error in sun position on sensor (centroid accuracy based on describes the azimuth and zenith angle on the error in center radiometric SNR, gain variation, and image distortion). SNR position, and the remaining parameters are described in Table 2. Notice for a ?xed zenith angle, errors in boresight pointing contribution believed to be small (image ~3 pixels and camera gain, may be corrected by the errors in center location. The expres sion may be rewritten in terms of an effective center point and large zenith angles is under investigation. divided into sensor row and column, exposure time set to ~200 counts out of 255, noise measured < 1 bit rms). Gain variation not measured. Image distortion, especially for (5) A A—Xe = fractional error in pixel size (based on linear fisheye x A XE response, more generally( Ax )0; should be re—placed as systematic error in measuring zenith angle). Response nonlinearity suspected problem. Correction under investigation (6) 005 = error in determining ?sheye boresight calibration parameters plus boresight drift (time/temperature). Fisheye boresight calibration  The calibration procedure takes advantage of this property by determining the center location which minimizes long term repeatability under investigation. (7) 09X = noise in inclinometer measurement. the azimuth error (in the least squares since) for a series of measurements at a constant (or near constant for sun) zenith  angle. The procedure is repeated for several zenith angles, and an additional error term which is proportional to the magni If the device is permitted to pitch and bank, there is the results are plotted as a function of tude of the pitch and/or bank of: Feb. 12, 2015 US 2015/0042793 A1 Inertial Navigation 1 2 sin 0S cos 0S 2 2 4 Ax e 2 —Sin20S Jahaie ] + I] + o‘as(l + cos 0;) + M )0;) s  One alternative to overcome these limitations Appli cants have added an inertial navigation component developed at Innalabs Inc. with o?ices located in Dullas, Virgina and image-based navigation system for position and weapon atti tude determination for indoor conditions developed by Evo lution Robotics with o?ices located in Pasadena, Calif. The  Where a contribution from the boresight zenith angle relative to inclinometer zenith has been omitted (as use of Innalabs component permits the minimization of the sumed negligible). The reader should note that this corre sponds to an rrns value instead of the variance shown for rate on module performance. The use of Evolution Robotics leveled operation. All of the error terms are the same as described in Table 3 with the exception of, sex, the inclinom eter measurement error. For pitched/banked operation, the inclinometer measurement error now includes not only noise, but any gain or nonlinearity contributions.  effect of environmental conditions and high angular motion image based navigation system permits determination of position and attitude during indoor exercises.  The memory-based optical navigation system includes a processor programmed with images of the envi ronment where the training is to take place. Images of the In addition to the error sources discussed above, the environment recorded by a camera mounted on the ri?e are measurements will have two additional error sources. The analyzed with special algorithms by a computer processor ?rst is the accuracy of the reference points. The second is pointing the Vector 21 (~1.2 mr reticule diameter). Current which determines, from the camera images and the pro rough estimate is that these error sources are on the order of  Embodiments of the present invention also include software permitting users to identify landmarks imaged by 0.5 mr rms.  Test data proving the accuracy of this embodiment utilized with the Victor 21 binoculars and with a theodolite is reported in parent patent application Ser. No. 12/283,785 which has been incorporated herein by reference.  grammed images, the pointing direction of the ri?e. the camera and to determine directions to those landmarks from speci?c locations during cloudless periods and to use tho se landmarks and directions as references for determining ri?e pointing directions when clouds obscure the sun or stars. Once the target is identi?ed, additional software determines the orientation of the camera. Astronomical algo rithms and celestial navigation software suitable for program ming computer 22 is described and provided in several well known texts including Astronomical Algorithms by Jean Meeus that is referred to in the Background Section. Once the camera orientation is known, the azimuth of the instrument is easily computed. Boresighting the Module with Other Instruments  Calibration of the module with other optical instru Single Camera and Multiple Cameras  Embodiments of the present invention can be designed for daytime operation based on the location of the sun and other embodiments can be designed for operation based on the position of the moon, the stars and other celestial objects such as man-made satellites. Or as described above with respect to FIGS. 1 through 9 the embodiments can be designed to operate day and night using a single camera. Alternatively as described in some of the parent application ments requires a single calibration. A target at a knowrement more than one camera can be included with at least one is made. The azimuth reported by the celestial measurements is then rotated to agree with the other optical instruments. designed for night-time use. Calibration Module is Separate  As indicated in FIG. 8 the calibration module (in cluding Ethernet PHY chip 70, 20 pin connector 72 and JTAG connector 68) is a separate module from the DPS Module 66 and circuit board and the optical components in order to minimize the size and weight of the celestial compass. Advantages and Limitations of the Celestial Compass  camera designed for day-time use and at least one camera  Applicants’ earlier versions of their celestial com pass included separate optical sensors optimized for daytime and nighttime operation along with two small digital cameras and miniature optical lenses. However, to meet the size, weight, and power requirements for determining pointing direction for ri?es, a single-sensor design is preferred. The challenge is that a very large sensor dynamic range of 101 l to 1013 must be accommodated in order to measure the position of both the sun and stars. Exposure time and gain control generally provide for a range of approximately 105 in illumi nation. To enhance the system’s dynamic range, Applicants A principal advantage of use of the celestial com have developed the ?lter described above. The mechanical pass as compared to a magnetic compass is that it can con neutral density ?lter described above provides the dynamic tinuously measure absolute heading relative to the Earth’s true north with accuracy of 1 mil without the use of pre emplaced infrastructure and does not rely on the use of mag netic compass. However the celestial compass shown in range required for day/night operation. A motor inserts or removes the ?lter in about 1 second for day/night operation. The motor is approximately the same size as the ?sheye lens. Focus maintained by using a very thin ?lter, such as 12 micron FIGS. 1 through 9 has limitations:  a) It cannot operate in the presence of heavy thick aluminized Mylar ?lm, such that the change in focus is negligible when the ?lter is inserted. An alternative ?lter clouds, fog, and smoke, and would be to use a glass ?lter with a transparent piece of glass or moon is obscured by trees, buildings or other struc adjacent to the ?lter glass. This second optic would maintain the optical path length, and would appear in the gap as the tures, for example, in urban environments. ?lter wheel rotates.  b) It cannot operate when line of sight to the sun Feb. 12, 2015 US 2015/0042793 A1 Imbedded Micro-Processor components can function in partly cloudy sky conditions.  The estimated number of operations required for the daytime sensor to determine target azimuth by imaging the for a clear day or night, of 0.1 mil, for a cloudy day of 0.753 sun is 40 million operations per second. As explained above a preferred micro-processor that meets this requirement is the BlackFin embedded processor ADSP BF537 available from Analog Devices. This processor has many several advanta geous features such as very low power consumption (400 Test results have demonstrated an RMS target azimuth error, mil, and for cloudy night of 0.75 mil.  When clouds, fog, or smoke interfere with celestial measurements using the celestial direction components, the inertial navigation components which includes continuous input from the magnetometer will serve as a “?y wheel” mW), a small size in a mini BGA package, a very low cost carrying the celestial ?x forward and determining the weap (approx. $45 in small quantities), and a scalable family of pin and code-compatible parts. The compatible parts allow the processor to ?t the application without requiring major on’s orientation. However, even in this case, the input from the magnetometer will include corrections (based on the last available azimuth measurement from the celestial direction changes to either the hardware or the ?rmware. components) which permit mitigation of the errors caused by the Earth’s declination angle and by large magnetic distur Inertial Navigation Component bances.  The celestial and inertial measurements features of the present invention complement each other well. The celes tial measurements are very accurate with essentially no drift over long intervals, but will only be available intermittently due to high sensor motion and environmental conditions. The inertial measurements have very high bandwidth and are accurate over short time periods, but suffer from drift over long time periods. The two are integrated in a typical Kalman ?lter architecture. All sensors (i.e. the optical sensor, the inclinometer, the inertial navigation component and the mag netic compass if one is used) feed data directly to the main processor. The main processor will implement a Kalman ?lter to optimally combine the inputs from all four sensors.  The Kalman ?lter will include estimates for the accelerometer gain and bias drift based on the GPS position updates, gyro gain and bias drift based on the magnetic com pass and the celestial sensor, and magnetometer bias drift based on the celestial measurements. Since the celestial mea surements constitute the most computationally intensive measurements, they will only be updated once every 10 sec onds. In the interim, the celestial sensors will be put in standby mode, and the processor clock will be reduced to  Finally, the above describe preferred embodiment has been designed for extremely low power consumption. Various modes of operation are provided: full sleep mode; ready, or stand-by, mode; and operational mode. In the stand by mode, the microprocessor requires less than 1 mW. Cloudy Weather  As indicated above in connection with the descrip tion of preferred embodiments. The primary components of the present invention cannot function as desired in cloudy weather or in similar situations when the celestial objects are not visible to the system’s sensors. For these reasons embodi ments may be equipped with a backup digital magnetic com pass.  This magnetic compass can be calibrated periodi cally using the features of the present invention and can take over when the heavens are obscured. Alternatively or in addi tion a miniature attitude and reference system such as the systems discussed in the background section of this speci? conserve power. Operation  Power Consumption In clear sky conditions day and night, the celestial direction components provides periodic precision azimuth measurements with respect to Earth’ s true north and provides periodic (every 10 seconds) updates to the Kalman ?lter. The module provides a key element to the initial alignment at start up. Based on celestial azimuth measurements, the Kalman ?lter estimates the magnetometer bias drift, as well as gyro gain and bias drift. This allows the module of the present invention to mitigate the errors related to the Earth’ s declina tion angle occurring over time. The inertial navigation com ponents correct for ri?e movement over short periods. Addi tionally, the lO-second updates eliminate errors associated with local magnetic disturbances. On the other hand, using inputs from the magnetometer, the effects of highly dynamic conditions on performance is mitigated. The inertial naviga tion components continuously measure the weapon’s motion cation may be added to allow the target information to be determined in the event that clouds obscure the celestial objects. Also when systems of the present invention is located at a particular location the precise location to a local landmark can be identi?ed by the system and utilized to provide refer ence directions later in the event of cloudy weather. To utilize this feature an additional camera may be required to assure that an appropriate local landmark is in the ?eld of view of system camera. Another alternative for direction determina tion when celestial objects are not visible is to include a sky polarization feature. Sky Polarization Feature  In order to characterize the polarization of sky light over any ?eld of view utilizing intensity measurements, a minimum of three measurements may be required. As explained in the background section, during daytime the sky and provide that information to the processor where it is used to determine the aiming direction of the ri?e. is polarized in circles around the sun even in cloudy con Partly Cloudy Skies measurements of intensity are made after the light has been made to pass through a linear polarizing ?lter. In order to make many such measurements over a region of the sky, several methods have been utilized or proposed:  Best results from the celestial direction components are achieved on cloudless days and nights. However these sitions. Applicants have determined that at night the sky is similarly polarized around the moon. Typically polarization Feb. 12, 2015 US 2015/0042793 A1  1.A telescope with a single-pixel intensity detec tor is scanned over the region of interest and a data taken for at least three orientations of an included polarizing ?lter at each position.  2. A telescope is scanned over the region of inter est. The light from a telescope is split and directed to at least three single-pixel intensity detectors, each with a ?xed polarizing ?lter oriented in an appropriate fashion. Reference Images  The result of polarized light traversing complicated optics could be extremely difficult to accurately characterize. (FPA) detector is utilized with a rotating polarizing ?lter. The optics could include numerous lenses and coatings with unknown manufacturing variations and defects. The light will pass through a polarizing ?lter at various angles with respect to the normal, and the properties of the polarizing ?lter will not be perfectly uniform. The focal plane array will have non-uniformities in the pixels. A simple way to circumvent these dif?culties is the following. Reference images are At least three exposures, each with a different orienta recorded of the sun in a clear sky, at various zenith angles,  3. A camera or a telescope with a focal plane array tion of the polarizing ?lter are required to acquire the necessary data.  4. The light from a camera lens or telescope is split a delivered to three FPA’s simultaneously. Each FPA has a ?xed polarizing ?lter oriented in an appropri ate fashion. Only one set of simultaneous exposures is required to collect data. Only one exposure is required to take data.  5. A single imaging camera or a telescope with a single FPA detector is used. Polarizing ?lters are asso ciated with individual pixels of a focal plane array. At least three orientations are utilized, and only a fraction of the pixels (1/3 at most) records information for a speci?c orientation of the polarizing ?lter. Only one exposure is required to take data.  There are issues with most of the above schemes. The sun (and moon) is continually moving, as are clouds. In order to make accurate measurements, the sun (or moon) and the atmosphere must be effectively frozen. Schemes l & 2 are not preferred, as they generally are too slow. Scheme 3 can be made to work, if the exposures are made at video rates, although some change in cloud pattern could occur over the using the ISPC. A reference angle-of-polarization (AOP) image is computed for each zenith angle and stored in a data base. The azimuth of the sun with respect to the ISPC is recorded with each reference image. The location of zenith in the AOP images is recorded with each reference image. In Use  In use, when a new image is recorded, the AOP image is computed and is compared to a reference AOP image with the same zenith angle. If necessary, the comparison reference AOP image is interpolated between two database images with zenith angles bracketing the zenith angle for the current data. Either the reference AOP image or the new AOP data image is mathematically rotated about zenith and the degree of correlation with the other used to determine the best match. The amount of rotation required to obtain the best match determines the azimuth offset of the current sun posi tion from that of the sun in the reference image, and deter mines the azimuth of the ISPC. required three frames. This can be accomplished utilizing ferroelectric liquid-crystal modulators. These in general are  Preferred embodiments of the present invention includes this hybrid azimuth sensing system will increase the availability of nonmagnetic highly accurate azimuth solution up to 85%; enabling operability to persist in cloudy skies, associated with narrow operating bandwidth and cannot be made to function in the ultraviolet. There are issues with completely overcast conditions and conditions when a line of-sight to the sun is obscured by trees, buildings, or other reproducibility of the polarization axis versus applied voltage structures, and even when a forward observer operates in a at different temperatures. Scheme 4 avoids these issues, but at hole with only a limited area of the sky available for viewing. the cost of three cameras and three ?lters instead of one each. Therefore a system based upon scheme 4 is more expensive, bulkier and heavier and consumes more power. Scheme 5 Additionally, the hybrid north ?nding system will also pro avoids all of the previous issues, although the data for each polarization axis is sparser, and must be interpolated. Although in cloudy skies the degree-of-polarization pattern can be quite noisy, the direction-of-polarization pattern is always determined primarily by single Rayleigh scattering, and the pattern is smooth and predictable. Hence sparse data does not present a fundamental problem. Therefore, scheme 5 is the best. Imaging Sky Polarization Compass  An imaging sky polarization compass (ISPC) con sists of ?ve principal components:  A wide-angle or ?sheye lens, or a simple aperture  A polarizing ?lter or ?lter array  A focal plane array sensor  An inclinometer to determine pointing of the optical axis of the lens with respect to zenith  A processor to control the camera, take the appro priate data and compute an azimuth vide accurate azimuth in twilight conditions during and after sunset and prior to and during sunrise, when celestial bodies are generally not visible. This capability is increasingly important in higher latitudes (i.e. polar regions) that experi ence much longer twilight hours.  Applicant’s sky polarization north ?nding system mimics a similar solution exploited by nature. As explained in the background section of this application, many insects and animals are known to use the sky polarization pattern for navigation. The hybrid azimuth sensing system will use a low-cost in-house polarizer-on-pixel technology to enable two operational modes: i) celestial mode when the sun is above the horizon and an imaging sensor is able to record the sun images or when the moon and stars are visible at night and ii) polarization mode, when the sun cannot be imaged by the sensor due to adverse weather conditions, or because the line-of-sight to the sun is obscured by trees, buildings, or other structures. This technology will increase the availability of azimuth solution for worldwide weather up to 85%. The hybrid system achieves a compact and lightweight form fac tor by cleverly leveraging common hardware architectures, including a ?sheye lens, processor and electronics board native to the Applicants’ celestial compasses described in the Feb. 12, 2015 US 2015/0042793 A1 parent applications listed in the third paragraph of this speci ?cation, for both the celestial and polarization-based north ?nding modules. FIG. 11 is an example showing histograms of the AOP difer ence between the polarization images and the reference images computed from the test data. Current single measure ment azimuth accuracy in partly cloudy conditions is in the Applicant’ s Experiments range from 0.10 to 0.30. Under conditions when the line-of  Applicants’ experiments hade demonstrated the sight to the Sun was blocked by clouds or by a nearby object imaging of bright stars in daytime using an infrared camera with a 50 mm lens, and azimuth sensing in overcast condi tions using the novel sky polarization measurement tech nique. Although longer wavelengths such as short wave infra red can better penetrate clouds and smoke, the ability to image the sun and stars is effectively eliminated with signi? cant levels of cloudiness. The sky polarization pattern, how ever, typically persists in completely overcast skies at a detectable level in the near ultraviolet spectral range. The sky polarization technique, demonstrated by Applicants exploits this very important phenomenon; enabling a path towards achieving an accurate all-weather azimuth solution.  By imaging a signi?cant portion of the sky, the signal-to-noise ratio and thus the single measurement accu racy can be improved. In poor sky conditions, the optimal regions of the sky for polarization measurements are more likely to be interrogated with a large ?eld-of-view. In cases with restricted access to the sky such as under canopies or in urban environments with tall buildings, a portion of the un obscured sky is likely to be found.  Applicants experiments have focused on developing and improving components for sky polarization measure ments; culminating in a sensor system based upon a rotating polarizing ?lter with an optical encoder to keep track of the polarizer angle and trigger the camera at the appropriate times. FIG. 10 shows an experimental setup. (building), the system performance is comparable to the clear sky conditions, 0.1°. System single measurement perfor mance is typically in the range from 0.3 to 0.5 degrees under fully overcast sky conditions.  Applicants anticipate accuracy gains will be achieved by (ii) increasing the FOV up to 180 degrees, (ii) increasing system dynamic range from 8 bits to 12 bits, (iii) increasing camera frame rate up to 120 Hz and averaging of multiple measurements, and (iv) improving image quality metric used for “good” pixel selection based on Malus Law. The use of the Malus Law pixel ?lter quali?es image data inputs to the azimuth calculation to further increase con? dence and accuracy.  Preferably miniature prototypes should incorporate polarizer-on-pixel technology in order to achieve size weight and power needs for appropriate to handheld applications, as well as to increase design robustness by eliminating moving parts. Ideally, the polarizers would be fabricated on the pixels at a foundry. However, this process is still in development and is too expensive to be a viable, near-term solution. For opti mum extinction coe?icient and transmission, the polarizers are ideally composed of high conductivity metal strips with a pitch signi?cantly smaller than the wavelength of interest. In the near ultraviolet range (350 nm) this means line pitches of the order of a few hundred nanometers or less. CMOS devices generated by Mukul Sarkar used a line pitch of 0.48 micron  The sky polarization compass software developed and was actually inadequate for use in the near ultraviolet. by Applicants uses the current sky AOP pattern and a pattern matching algorithm to ?nd the best reference image of the Utah, has developed a process for depositing parallel alumi AOP with known sun azimuth and elevation angle stored in a digital library. The use of a pattern matching technique elimi nates the need to take into account the effect of the optical system on the state of polarization detected at each pixel. The key steps of determining target azimuth using sky polariza tion compass are the following:  Record sky polarization images and create a digi tal library of wide angleAOP and DOP reference images under clear sky conditions for a range of solar elevation angles  Record sky AOP and DOP images for the current known location and time  Calculate the solar elevation angle for the current location and time  Select reference image data that matches the cur rent solar elevation  Find the best match between the two images using the pattern matching algorithm  Calculate current azimuth position of the Sun relative to the Sun position at the time of the reference image  Calculate true North reference  Determine target azimuth.  The rotating polarizer sky compass was demon strated under various sky conditions. Sky images were taken for a ?xed (standard) orientation of the system using a spot ting scope pointing at a reference marker located about one half mile across a canyon from the sky compass equipment. Polarization images and reference images were compared.  Altemately, Moxtek, lnc., with of?ces in Orem, num nanowires onto glass substrates in intricate patterns and with pitch adequate for use to 300 nm wavelength. They can produce micro-polarizer arrays matching the pixel pitch of any focal plane array. These micro-polarizer arrays can be “glued” onto commercial off-the-shelf focal plane arrays (FPAs) to cost-effectively convert them to polarizer-on-pixel sensors. This is the preferred approach Applicants proposes for near term, low-cost polarizer-on-pixel sensors. Applications  The military uses compasses to determine the azi muth of surrounding locations and targets. However, conven tional magnetic or digital-magnetic compasses are sensitive to the nearby presence of metals and alloys such as iron. However, much of military equipment, including vehicles, armament and weapons include such materials. Hence a non magnetic compass is highly desired. The sky polarization compass is insensitive to the presence of magnetically active materials such as iron. By combining a sky polarization com pass with GPS in a cell phone or other device containing a GPS receiver, the device becomes capable of pointing to known objects, or equally to displaying the azimuth of objects at which the device is pointed at. This could permit, for instance, a cell phone to point to the door of the emergency room, or any other known landmark. One could be guided more accurately and ef?ciently to a known destination, when the device can point. A backpacker in the Sierra mountain range could use a GPS receiver augmented with a sky polar ization compass to determine which of the jagged points on a Feb. 12, 2015 US 2015/0042793 A1 ridge, was actually Mount Whitney, and which gully is the Mountaineer’s Route. All of this is possible, because the device can now accurately point to items of interest.  The imaging sky polarization compass can be used Test Results  Actual test results of prototype units con?rm that the accuracy of Applicants compasses are about an order of mag nitude better than magnetic compasses. As indicated in the to determine the direction of zenith. The angle-of-polariza Background section magnetic compasses under ideal mag tion pattern in the sky is symmetric about the solar meridian, the plane containing the observer, the sun and zenith. Within this plane are two neutral points, the Arago and Babinet points, which are readily identi?able in the processed images. netic conditions operate with a measurement error typically in the range of about 10 to 17 milliradians which results in a The positions of the two neutral points and the sun from zenith are all known, so if any of the three are visible, then the location of zenith is also determined. Hence the requirement of a separate inclinometer device to determine vertical is unnecessary. This might be particularly useful on moving platforms such unmanned aircraft, airplanes, boats, ground vehicles, missiles, etc, on which an inertial sensor for deter mination of vertical is dif?cult if not impossible.  locator error of about 50 to 85 meters at a 5 km range. Applicants’ celestial compasses (with the sun, moon or vis ible stars at least 45 degrees off zenith (vertical)) operate with an a measurement error in the range of about 1 to 2 millira dians which corresponds to a locator error of about 5 to 10 meters at the 5 km range.  There are many variations to the above speci?c embodiments of the present invention. Many of these will be obvious to those skilled in the art. For example in many embodiments focal plane arrays with only about 350,000 pixels will be adequate. Preferably time should be accurate to The sky polarization compass uses knowledge of at least three seconds. For a less expensive system, the inertial time and approximate position, along with sky polarization navigation system and the memory-based navigation could be data to determine a very accurate value for the absolute azi omitted. In this case the system would in general not be muth of the device, and thus the absolute azimuth of sur rounding objects and landmarks. It is possible to use the mechanism backwards to determine location. This could be advantageous, for instance, in a GPS denied environment. The direction of vertical can be determined either from the sky polarization pattern and the position of the sun or neutral point, or from an included inclinometer. The time could be determined using a clock of suf?cient accuracy. The azimuth of the sun could be determined through the use of the sky polarization pattern in combination with the use of a conven operative in cloudy weather. However, local landmarks that tional magnetic or digital-magnetic compass. With this data, geographic location can be determined.  It is possible to use the mechanism backwards to are visible to the camera could be substituted for celestial objects if the system is properly calibrated using celestial information to determine the position of the landmarks. Operators could also install a substitute landmark to use in this situation. These landmarks could also be used in the full system with the inertial navigation for re-calibration in the event of cloudy weather. So the scope of the present invention should be determined by the appended claims and their legal equivalence. What is claimed is: 1. A celestial compass comprising: A) a camera system adapted for viewing at least portions of a GPS denied environment. The direction of vertical can be the sky and comprising: 1) a telecentric ?sheye lens, determined either from the sky polarization pattern and the 2) a sensor having a focal plane array of at least 350,000 determine time. This could be advantageous, for instance, in position of the sun or neutral point, or from an included inclinometer. The azimuth of the sun could be determined through the use of the sky polarization pattern in combination with the use of a conventional magnetic or digital-magnetic compass. If the geographic location is also known from topography or landmarks, then the time is determined.  Embodiments of the present invention include in many applications where high accuracy directional equip ment is needed such as for use in surveying, on cruise ships, ?shing boats and private and commercial aircraft. The inven tion may also be utilized on robotic vehicles including unmanned aerial vehicles, unmanned marine vehicles and unmanned surface vehicles. A particular important use of the invention will be as a guidance and control feature for robotic vehicles designed for use in dangerous situations where accu rate directional information is required. For example, in addi tion to the telescopic equipment the celestial camera and the MEMS mirror of the present invention, the robotic surveil lance vehicle could be equipped with a GPS unit, and a backup digital magnetic compass and a camera for monitor pixels, and B) an inclinometer C) a processor programmed with a celestial catalog pro viding known positions at speci?c times of at least one celestial object and algorithms for automatically calcu lating target direction information based on the inclina tion of the system as measured by the inclinometer and the known positions of at least two celestial objects as provided by the celestial catalog and as imaged by the camera, D) a polarization ?lter orpolarization ?lter array adapted to permit the camera system to measure polarization of light from a plurality of regions of the sky so as to determine location of at least one celestial object. 2. The compass as in claim 1 wherein the at least one celestial object comprises the sun and the moon. 3. The compass as in claim 1 wherein the at least one celestial object comprises the sun. 4. The compass as in claim 1 wherein the camera system also comprises a movable ?lter unit comprising an optical ing the ?eld of view of the telescopic equipment. Communi ?lter and adapted to block portions of sunlight to permit day cation equipment would be needed for remote control of the robotic vehicle. Utilizing features described in the embodi ments described above dangerous targets could be identi?ed and neutralized. Embodiments could include weapons for defense or even offence which could be operated remotely. time and night time operation of the kit with the single camera system; 5. The celestial compass as in claim 1 wherein the at least one celestial object is the sun, the moon and a plurality of stars.