Coordinate System. TRIMBLE Survey Controller Software

Coordinate System

Coordinate System

A coordinate system consists of a projection and datum transformation and, sometimes, additional horizontal and vertical adjustments.

When you create a job, select a coordinate system by one of the following methods:

•

Scale factor only

•

Select from library

•

Key in parameters

•

No projection/ no datum

•

Broadcast RTCM

If you need to perform a GNSS site calibration, or change the parameters manually after selecting the coordinate system, select Files / Properties of current job / Coord. sys.

Where the job parameters are keyed in, or a calibration is used, the coordinate system settings are displayed as

"Local site".

If you modify the coordinate system by calibration or by manually changing the parameters, you must do so before you compute offsets or intersection points, or stake out points in the local coordinate system.

To set up a

ground coordinate system for the job, choose the Select from library or Key in parameters option.

To customize the coordinate systems available on the Trimble Survey Controller software, use the Coordinate

System Manager software. For more information see

Customizing the Coordinate System Database.

Customizing the Coordinate System Database

You can customize the coordinate system database used by the Trimble Survey Controller software. This enables you to:

•

Reduce the number of coordinate systems available in the Trimble Survey Controller software so that

• it includes only the ones you need.

Customize existing coordinate systems definitions or add new coordinate system definitions.

•

Include GNSS site calibrations in the coordinate system library.

You must use the Coordinate System Manager software to modify the Coordinate System Database (CSD) and then transfer the modified database to the [Trimble data] folder on the Trimble controller. When a

[custom.csd] file exists in the [Trimble data] folder, the Trimble Survey Controller software uses the custom.csd database instead of the coordinate system database built into the Trimble Survey Controller software.

431

Note - The Coordinate System Manager software is installed at the same time as your Trimble Office software, for example, Trimble Geomatics Office.

There are a number of ways you can use the Coordinate System Manager software to customize the coordinate systems. From the following options, choose the one that best suits your needs.

To reduce a coordinate system library to one or more coordinate systems, zones, and sites:

1. Run the Coordinate System Manager software on your office computer.

2. Do one or more of the following to hide the required element:

♦

Coordinate system: In the left pane of the Coordinate Systems tab, select the coordinate

♦ system(s) that you do not want, right click and then select Hide.

Zone: In the left pane of the Coordinate Systems tab, select a coordinate system, from the

♦ right pane, select the Zone(s) you do not want, right click and then select Hide.

Site: From the Sites tab, right click the site(s) you do not want and then select Hide.

3. Select File / Save As.

4. Name the file [custom.csd] and then click Save.

By default, the file is saved in [Program Files\Common Files\Trimble\GeoData] with the extension *.csd.

To export only User defined coordinate systems:

1. Run the Coordinate System Manager software on your office computer.

2. Select File / Export.

3. Select User-defined records only and then click OK.

4. Name the file [custom] and then click Save.

By default, the file is saved in [Program Files\Common Files\Trimble\GeoData] with the extension *.csw.

Tips for using the Coordinate System Manager software

♦

To make multiple selections, press CTRL or SHIFT.

♦

To hide records, right click the selection and then select Hide.

♦

To display hidden records, select View / Hidden Records. Hidden records are displayed with a

♦ dark red icon.

To unhide hidden records, right click hidden record(s) and then clear the Hide check box.

For more information, see the Coordinate System Manager Help.

Note - If a GNSS site calibration has been saved using your Trimble Office software, a site with the assigned name is added to the Sites tab and a Site group is created in the Coordinate Systems tab, if required. When you create a customized coordinate system that includes sites saved by the Trimble Office software, include those sites created in the Sites tab. The Site group in the Coordinate Systems tab contains the coordinate system details referenced by the sites saved in the Sites tab, but the calibration details are only stored in the site in the Sites tab.

Transferring Customized Coordinate Systems

432

You can transfer the file to the controller using the Trimble Data Transfer utility or Microsoft ActiveSync technology. The file must be called [custom.csd] for the Trimble Survey Controller software to access it.

A file transferred by the Data Transfer utility is automatically renamed and saved to the [Trimble data] folder.

If you transfer the file using ActiveSync technology, you must copy the file to the [Trimble data] folder and then rename the file to [custom.csd].

For more information on transferring a file from a Trimble controller to an office computer, see

Connecting the controller to the office computer using Microsoft ActiveSync technology.

If you are using the Data Transfer utility, when the Open dialog appears, select CSD Files (*.csd) or CSD

Files (*.csw) from the Files of type list.

To select a custom site in Trimble Survey Controller software:

1. From the main menu, select Files / New job.

2. Enter the Job name.

3. In the Properties group, tap the Coord sys button.

4. Choose Select from library and then tap Next, if required.

5. In the System field, select [User sites].

6. In the Site field, select the required site.

7. If required, select a geoid model.

8. To return to the New job dialog, tap Store.

9. In the New job dialog, tap Accept to save the new job.

Scale Factor Only

Use this projection type when you are doing a conventional-instrument only survey with a local scale factor.

This option is useful for areas that use a local scale factor to reduce distances to the local coordinate system.

To choose a Scale factor only projection:

1. Create a new job.

2. Select Scale factor only from the Select coordinate system menu.

3. Enter a value in the Scale field and then tap Store.

Projection

A projection is used to transform local geodetic coordinates into local grid coordinates.

Note - Enter an appropriate default height value for the Trimble Survey Controller software to correctly calculate a sea level correction and then apply it to the grid coordinate.

GNSS coordinates are relative to the WGS-84 ellipsoid. To work in local grid coordinates, you must specify a projection and datum transformation.

433

You can specify a projection:

• when a job is created and you have to choose a coordinate system (select from a list, or key in)

• during a survey (you calculate values by performing a calibration)

• in the Trimble Geomatics Office software, when the data is transferred.

Do not change the coordinate system or calibration after you have staked out points, or computed offset or intersection points.

If a projection and datum transformation are specified, you can reduce any discrepancies between the

WGS-84 coordinates and the local grid coordinates by performing a site calibration.

Ground Coordinate System

If you require coordinates to be at ground level instead of projection level, use a ground coordinate system.

When you select a ground coordinate system, grid distances equal ground distances.

To set up a ground coordinate system, when you create a job:

1. Specify a coordinate system by choosing the Select from library, or Key in parameters option.

2. To use ground coordinates with the selected coordinate system, tap the Page down button, and then from the Coordinates field, do one of the following:

♦

To key in a scale factor, select Ground (Keyed in scale factor).

♦

To let the Trimble Survey Controller software calculate the scale factor, select Ground

(Calculated scale factor). Enter values in the Project Location group to compute the scale factor.

The computed scale factor allows for the projection scale factor at the Project Location in order to ensure that the combined factor (grid scale factor plus elevation factor) at the Project Location equals

1.

The Trimble Survey Controller software applies the ground scale factor to the projection.

3. To add offsets to the coordinates, enter a value in the False northing offset and False easting offset fields as required.

Note - When working with a ground coordinate system the reported ground distance may not be the same as the reported grid distance. The reported ground distance is simply the ellipsoid distance corrected for the average height above the ellipsoid. However the grid distance is computed between the ground coordinates of the points, and is therefore based on a coordinate system that provides a combined scale factor of 1 at the

Project Location.

Note - Use offsets to differentiate ground coordinates from unmodified grid coordinates.

434

Project Height

The project height can be defined as part of the coordinate system definition when creating a new job. To find it, select Files / Properties of current job for a coordinate system in either the Library or Key in projection dialogs.

If a point has no elevation, the Trimble Survey Controller software uses the project height in Cogo calculations. If you combine GNSS and 2D conventional observations, set the Project height field to approximate the height of the site. This height is used with 2D points to calculate grid and ellipsoid distances from measured ground distances.

In 2D surveys where a projection has been defined, enter a value for the project height that approximates the height of the site. You need this value to reduce measured ground distances to ellipsoid distance, and to compute coordinates.

If you edit the project height (or any other local site parameter) after calibrating, the calibration becomes invalid and must be reapplied.

No Projection / No Datum

To select a coordinate system with an undefined projection and datum, when you create a job:

1. Tap the Coord. sys button and select No projection/no datum.

2. Set the Coordinates field to Ground, and enter a value (average site height) in the Project height field to use ground coordinates after a site calibration. Alternatively, set the Coordinates field to Grid.

3. Select the Use geoid model check box, and select a geoid model to calculate a Geoid/Inclined plane vertical adjustment after a site calibration.

Tip - Tap Here to automatically complete the Project height field using the current autonomous height derived by the GNSS receiver.

Any points measured using GNSS are displayed only as WGS84 coordinates. Any points measured using a conventional instrument are displayed with null (?) coordinates.

The Trimble Survey Controller software performs a calibration that calculates a Transverse Mercator projection and a Molodensky three-parameter datum transformation, using the supplied control points. The project height is used to compute a scale factor for the projection so that ground coordinates can be computed at elevation.

Broadcast RTCM

A Network RTK provider can configure a VRS network to broadcast RTCM messages that include some of the coordinate system definition parameters. When the Broadcast format is set to RTCM RTK, and the broadcast datum definition messages are broadcast by the VRS network, Trimble Survey Controller can use this to provide the datum and ellipsoid definition for a job.

435

When creating a new job to use with Broadcast RTCM, select Broadcast RTCM from the Select coordinate system screen, along with the appropriate projection parameters.

Trimble Survey Controller supports a subset of the RTCM transformation parameters, as shown below:

Transformation message

1021

1022

Details

Helmert/Abridged Molodenski (Control)

Molodenski-Badekas Transformation (Control)

1023

1024

1025

1026

1027

Ellipsoidal Datum Shift Grid Residual

Plane Grid Residual

Projection

Projection Lambert Conformal Conic Two Parallel

Projection Oblique Mercator

1028 Local Transformation

Supported

Yes

Yes

Yes

No

No

No

No

No

The RCTM broadcast message must contain either the 1021 or the 1022 control message. This defines what other messages will be present. All other messages are optional.

Datum shift grid values are broadcast at fixed time intervals for a grid surrounding the area you are working in. The size of the grid that is broadcast depends on the density of the source grid data. To perform coordinate system transformations, the grid file that is built by Trimble Survey Controller must include shift grids covering the location of points you are transforming. When you move to a new location, a new set of datum shift grid values is broadcast and there may be a slight delay until the appropriate values are received from the

VRS network server.

The broadcast transformation messages include a unique identifier for the broadcast parameters. If the broadcast parameters change, the identifier changes, and the Trimble Survey Controller creates a new grid file to store the new datum grid shift values.

If the broadcast RTCM transformation changes, Trimble Survey Controller shows the following message: The broadcast coordinate system has changed. Create a new grid file and continue?

•

If you select Yes, the system creates a new grid file, or, if it exists, uses another grid file that matches the newly broadcast transformation. If you change grid files, the new grid file may not cover the same area as the old grid file, so Trimble Survey Controller may not be able to transform points where there

• are 'holes' in the grid file.

If you select No, you cannot continue surveying. Create a new job and start the survey again. If you need access to data in the old job, link that job.

If you copy a job that is defined to use a Broadcast RTCM datum onto a different controller, and you do not copy the grid file, or if you delete the grid file on the controller, then Trimble Survey Controller does not have the appropriate grid file to perform the transformation and grid coordinates are not available. Similarly, if the controller with the copied job already has a grid file, but the grid file does not cover the area of the copied job, then coordinate transformation is not possible.

436

Notes

•

When a Trimble Survey Controller job with broadcast RTCM data is exported as a DC file, the GNSS

• observations are output as grid positions.

A Trimble Survey Controller job with broadcast RTCM data cannot be imported to Trimble Business

Center software version 2.0 or earlier.

Horizontal Adjustment

A horizontal adjustment is a least-squares adjustment that is applied to minimize the differences between transformed grid coordinates and local control points.

Horizontal and vertical adjustments are calculated if you perform a calibration when a projection and datum transformation are defined.

Trimble recommends that you use a minimum of four control points to compute a horizontal and vertical adjustment.

Alternatively, you can key in horizontal adjustment parameters when you start a new job.

Vertical Adjustment

This is a least-squares adjustment that is applied to convert (ellipsoid) heights to elevation. It is computed when you do a calibration. A minimum of one point is required to compute the adjustment. If more points are used, an inclined plane adjustment can be calculated.

If you have a geoid model selected, you can choose to use only the geoid model, or to use the geoid model and do an inclined plane adjustment. Trimble recommends that you use a geoid model to obtain more accurate orthometric heights from your GNSS measurements.

You can specify the type of vertical adjustment when you create a job. Set this parameter when you choose the coordinate system. You can also key in the parameters when you create a job.

To change the parameters for the current job, from the main menu select Files / Properties of current job, tap

Coord sys and then select Key in parameters / Vertical adjustment.

Note - When the Projection is set to Scale factor only, the Datum transformation, Horizontal adjustment, and

Vertical adjustment options are not available. Select a non Scale factor only projection to access the other parameters.

Coordinate Systems

Before starting a GNSS survey, decide which coordinate system to use. This topic discusses some things to consider when making this decision.

437

Choosing a Coordinate System for a Conventional Survey

Choosing a Coordinate System for a GNSS Survey

Choosing a Coordinate System for a Broadcast RTCM Survey

GNSS Coordinate System

Local Coordinate Systems

Calibration

Using a Datum Grid File

Using a Geoid Model

Trimble Geoid Models - WGS-84 versus Local Ellipsoid Based Geoid Models

Working with Ground Coordinates

If you intend to combine conventional observations with GNSS measurements, read the whole of this topic.

To make only conventional observations, see

Choosing a Coordinate System for a Conventional Survey.

Choosing a Coordinate System for a Conventional Survey

When surveying using conventional equipment, it is important to choose a suitable coordinate system.

For example, if a job is to combine GNSS measurements with conventional observations, choose a coordinate system that lets you view GNSS observations as grid points. This means that you must define a projection and a datum transformation. For more information, see

Creating a job.

Note - You can complete the field work for a combined survey without defining a projection and a datum transformation, but you will not be able to view the GNSS observations as grid coordinates.

If you want to combine GNSS measurements with two-dimensional conventional observations, specify a project height for the job. For more information, see

Project Height.

If a job is to contain conventional observations only, select one of the following when you create the job:

•

A typical coordinate system and zone that provide mapping plane coordinates. For example, State

•

Plane coordinates.

Scale factor only.

In a conventional survey, measurements are made at ground level. To compute coordinates for these measurements, observations are reduced to grid level. The specified scale factor is applied to measured distances to reduce them from ground to grid.

The Scale factor only option is useful for areas that use a local scale factor to reduce distances to grid.

438

Tip - If you are not sure what coordinate system to use, select the Scale factor only projection and enter a scale factor of 1.000.

Choosing a Coordinate System for a GNSS Survey

When you create a new job, the Trimble Survey Controller software prompts you to define the coordinate system you are using. You can select a system from the library, key in the parameters, select Scale factor only,

or select No projection / no datum transformation. For more information, see Creating a job.

The most rigorous coordinate system consists of four parts:

• datum transformation

• map projection

• horizontal adjustment

• vertical adjustment

Note - To conduct a realtime survey in terms of local grid coordinates, define the datum transformation and map projection before starting the survey.

Tip - In the Coordinate view field, select Local to display local geodetic coordinates. Select Grid to display local grid coordinates.

When WGS84 coordinates are transformed onto the local ellipsoid, using a datum transformation, local geodetic coordinates result. Local geodetic coordinates are transformed into local grid coordinates using the map projection. The result is Northing and Easting coordinates on the local grid. If a horizontal adjustment is defined, it is applied next, followed by the vertical adjustment.

Choosing a Coordinate System for a Broadcast RTCM Survey

When you create a new job, the Trimble Survey Controller software prompts you to define the coordinate system you are using. When surveying with VRS and the

RTCM broadcast includes coordinate system

parameters, create the job with the Datum set to Broadcast RTCM. To do this, select Broadcast RTCM from the Select coordinate system screen and then select the appropriate coordinate system to use from the available library definitions.

You can also use Key in parameters to enter your own specific projection definition. When you key in the parameters for the projection definition, make sure that the Datum transformation is set to Broadcast RTCM.

To do this, tap the Datum trans button and then select Broadcast RTCM, before you save the coordinate system definition.

GNSS Coordinate System

GNSS measurements are referenced to the 1984 World Geodetic System reference ellipsoid, known as

WGS84. However, for most survey tasks, results in terms of WGS84 have little value. It is better to display and store results in terms of a local coordinate system. Before you start a survey, choose a coordinate system.

Depending on the requirements of the survey, you can choose to give the results in the national coordinate system, a local coordinate grid system, or as local geodetic coordinates.

439

When you have chosen a coordinate system, search your survey archives for any horizontal and vertical control points in that coordinate system that are in the area to be surveyed. You can use these to calibrate a

GNSS survey. For more information, see

Calibration.

Local Coordinate Systems

A local coordinate system simply transforms measurements from a curved surface (the earth) onto a flat surface (a map or plan). Four important elements constitute a local coordinate system:

• local datum

• datum transformation

• map projection

• calibration (horizontal and vertical adjustments)

When you survey using GNSS, consider each of these.

Local Datum

Because an exact model of the earth's surface cannot be created mathematically, localized ellipsoids

(mathematical surfaces) have been derived to best represent specific areas. These ellipsoids are sometimes referred to as local datums. NAD83, GRS80, and AGD66 are examples of local datums.

Datum Transformation

GNSS is based on the WGS84 ellipsoid, which is sized and positioned to best represent the entire earth.

To survey in a local coordinate system, the WGS84 GNSS positions must first be transformed onto the local ellipsoid using a datum transformation. Three types of datum transformation are commonly used.

Alternatively, you can choose not to use a transformation at all.

The datum transformations are as follows:

• three-parameter - This assumes that the rotational axis of the local datum is parallel with the rotational axis of WGS84. The three-parameter transformation involves three simple translations in

X, Y, and Z. The three-parameter transformation that the Trimble Survey Controller software uses is a Molodensky transformation, so there may also be a change in ellipsoid radius and flattening.

Note - Positions on a local datum are commonly called "local geodetic coordinates". The Trimble Survey

Controller software abbreviates this to "Local".

•

Seven-parameter - This is the most complex transformation. It applies translations and rotations in

•

X, Y, and Z, as well as a scale factor.

Datum grid - This uses a gridded data set of standard datum shifts. By interpolation, it provides an estimated value for a datum transformation at any point on that grid. The accuracy of a datum grid depends on the accuracy of the gridded data set it uses. For more information, see

Using a Datum

Grid File.

Map Projection

440

Local geodetic coordinates are transformed into local grid coordinates using a map projection (a mathematical model). Transverse Mercator and Lambert are examples of common map projections.

Note - Positions on a map projection are commonly called "local grid coordinates". The Trimble Survey

Controller software abbreviates this to "Grid".

Horizontal and Vertical Adjustments

If published datum transformation parameters are used, slight discrepancies can exist between local control and GNSS-derived coordinates. These discrepancies can be reduced using minor adjustments. The Trimble

Survey Controller software calculates these adjustments when you use the Site calibration function. They are called horizontal and vertical adjustments.

Calibration

Calibration is the process of adjusting projected (grid) coordinates to fit the local control. You can key in a calibration, or let the Trimble Survey Controller software calculate it. You should calculate and apply a calibration before:

• staking out points

• computing offset or intersection points

The rest of this section describes how to perform a calibration using the Trimble Survey Controller software.

To key in a calibration, see

Creating a job.

Calibration Calculations

Use the Trimble Survey Controller software system to perform a calibration in one of two ways. Each method results in the computation of different components, but the overall result is the same if enough reliable control points (coordinates in your local system) are used. The two methods are:

•

If you use published datum transformation parameters and map projection details when creating a job, and if you provide enough control points, the Trimble Survey Controller software performs a calibration that computes horizontal and vertical adjustments. Horizontal control points allow scale error anomalies in the map projection to be removed. Vertical control allows local ellipsoid heights to be transformed into useful orthometric heights.

Tip - Always use published parameters if they exist.

•

If you do not know the map projection and datum transformation parameters when creating the job and defining the local coordinate system, specify No projection / no datum.

Then specify whether grid or ground coordinates are required after a site calibration. When ground coordinates are required, you must specify the project height. In this case, the Trimble Survey

Controller software performs a calibration that calculates a Transverse Mercator projection and a

Molodensky three-parameter datum transformation using the supplied control points. The project height is used to compute a ground scale factor for the projection so that ground coordinates are computed at that height.

441

The following table shows the output of a calibration when various data is supplied.

Yes

Projection

Yes

No

No

Datum transformation

Yes

No

Yes

No

Calibration output

Horizontal and vertical adjustment

Datum transformation, horizontal and vertical adjustment

Transverse Mercator projection, horizontal and vertical adjustment

Transverse Mercator projection, zero datum transformation, horizontal and vertical adjustment

Local Control for Calibration

Trimble recommends that you observe and use a minimum of four local control points for the calibration calculation. For best results, local control points should be evenly distributed over the job area as well as extending beyond the perimeter of the site (assuming that the control is free of errors).

Tip - Apply the same principles as you would when placing control for photogrammetric jobs. Make sure that the local control points are evenly distributed to the extent of the job area.

Why Calibrations Are Needed

If you calibrate a project and then survey in real time, the Trimble Survey Controller software gives real-time solutions in terms of the local coordinate system and control points.

Operations That Require Calibration

Note - Perform a calibration at any time, but always complete the calibration before staking out any points, or computing offset or intersection points.

If no datum and no projection are defined, you can only stake out lines and points that have WGS84 coordinates. Displayed bearings and distances are in terms of WGS84.

Specify a projection before staking out arcs, roads, and DTMs. The Trimble Survey Controller software does not assume that WGS84 is the local ellipsoid, so you must also define a datum.

Without a datum transformation, you can only start a real-time base survey with a WGS84 point.

For information on how to perform a calibration, see

Calibration.

The following diagram shows the order of calculations performed when a calibration is calculated.

442

Copying Calibrations

You can copy a calibration from a previous job if the new job is completely encompassed by that initial calibration. If a portion of the new job lies outside the initial project area, introduce additional control to cover the unknown area. Survey these new points and compute a new calibration. Use this as the calibration for the job.

Tip - To copy the calibration from an existing job to a new job, make sure that the current job you want to copy has the calibration that you require in the new job. Then create the new job. A new job uses the default values from the previous job. Use the softkeys on the Job properties screen to change the defaults.

Using a Datum Grid File

A datum grid transformation uses interpolative methods to estimate the value of the datum transformation at any point in the area covered by the datum grid files. Two gridded datum files are required for this

443

interpolation-a latitude datum grid file and a longitude datum grid file. When you export a datum grid using the Trimble Geomatics Office software, the two datum grid files associated with the current project are combined into a single file for use in the Trimble Survey Controller software.

Selecting a Datum Grid File

To select a datum grid file when creating a job, do one of the following:

•

Select a coordinate system from the library provided in the Trimble Survey Controller software.

•

Select the Use datum grid check box. In the Datum grid field, select the file that you want to use.

Key in the coordinate system parameters. Select Datum transformation and set the Type field to

Datum grid. In the Datum grid field, select the file that you want to use.

Note - The U.S. State Plane 1927 and the U.S. State Plane 1983 coordinate systems in the Trimble Survey

Controller software use three-parameter transformations.

To select a datum grid file for use in the current job:

1. From the main menu, select Files / Properties of current job - Coord. Sys.

2. Do one of the following:

♦

If Key in parameters is selected, select Next. Select Datum transformation and set the Type

♦ field to Datum grid. In the Datum grid field, select the file that you want to use.

If Select coordinate system is selected, select Next. Select the Use datum grid check box. In the Datum grid field, select the file that you want to use.

The semi-major axis and flattening values for the selected datum grid file are displayed. These details overwrite any already provided by a specified projection.

Using a Geoid Model

The geoid is a surface of constant gravitational potential that approximates mean sea level. A geoid model or

Geoid Grid file (*.ggf) is a table of geoid-ellipsoid separations that is used with the GNSS ellipsoid height observations to provide an estimate of elevation.

The geoid-ellipsoid separation value (N) is obtained from the geoid model and is subtracted from the ellipsoid height (H) for a particular point. The elevation (h) of the point above mean sea level (the geoid) is the result. This is illustrated in the following diagram.

444

Note - For correct results, the ellipsoid height (H) must be based on the WGS-84 ellipsoid.

When you select geoid model as the vertical adjustment type, the Trimble Survey Controller software takes the geoid-ellipsoid separations from the geoid file chosen, and uses them to display elevations on the screen.

The benefit of this function is that you can display elevations without having to calibrate on elevation benchmarks. This is useful when local control or benchmarks are not available, as it makes it possible to work

"on the ground" rather than on the ellipsoid.

Note - If you are using a geoid model in a Trimble Geomatics Office project, make sure you transfer that geoid file (or the relevant part of it) when transferring the job into a Trimble controller.

Selecting a Geoid File

To select a geoid file when creating a job, do one of the following:

•

Select a coordinate system from the library provided in the Trimble Survey Controller software.

•

Select the Use geoid model check box. In the Geoid model field, select the file to be used.

Key in the coordinate system parameters. Select Vertical adjustment and set the Type field to Geoid

model or Geoid/Inclined plane as required. (Select Geoid/Inclined plane if you intend to key in the inclined plane adjustment parameters.)

To select a geoid file for the current job:

1. From the main menu select Files / Properties of current job - Coord. Sys.

2. Do one of the following:

♦

If the Key in parameters screen is selected, select Next. Select Vertical adjustment and set the

Type field to Geoid model or Geoid/Inclined plane as required. (If you intend to key in the

♦ inclined plane adjustment parameters, select Geoid/Inclined plane.)

If the Select coordinate system screen is selected, select Next. Select the Use geoid model check box. In the Geoid model field, select the file to be used.

Trimble Geoid Models - WGS-84 versus Local Ellipsoid Based Geoid Models

Caution - Geoid models are traditionally based on global WGS-84 and prior to Trimble Survey Controller version 12.47, were always treated as global WGS-84 based geoid models even when they might have been based on local ellipsoid geoid models.

Trimble geoid models are now applied with respect to the interpolation method set in the geoid file, enabling both global WGS-84 and local ellipsoid based geoid models to be supported.

For more information, see Trimble Geoid Models - WGS-84 versus Local Ellipsoid Based Geoid Models.

Working with Ground Coordinates

If you need coordinates to be at ground level instead of projection level (for example, in areas of high elevation), use a ground coordinate system.

When you select a ground coordinate system, grid distances equal ground distances.

445

Setting up a Ground Coordinate System

When you set up a ground coordinate system in a Trimble Survey Controller job, the software applies a ground scale factor to the coordinate system projection definition.

To set up a ground coordinate system when creating a job:

1. Define the coordinate system for the job. Do one of the following:

♦

Choose the Select from library option to select a coordinate system from the library provided

♦ in the Trimble Survey Controller software. Tap Next.

Choose the Key in parameters option to key in the coordinate system parameters. Tap Next and then select Projection.

2. In the Coordinates field, choose an option to define the ground scale factor.

Additional fields appear below the Coordinates field.

3. If you select the Ground (keyed in scale factor) option, enter a value in the Ground scale factor field.

4. In the Project location group, enter values in the fields as required. Tap Here to enter the current autonomous position derived by the GNSS receiver. The autonomous position is displayed in terms of

WGS-84.

The project height is used with 2D points to reduce ground distances in Cogo calculations. For more

information, see Project Height.

If you select the Ground (calculated scale factor) option, the fields are used to calculate the ground scale factor. When the fields are completed, the computed ground scale factor is displayed in the Ground scale factor field.

5. To add offsets to the coordinates, enter a value in the False northing offset and False easting offset field, as required.

Note - Use offsets to differentiate ground coordinates from unmodified grid coordinates.

To configure a ground coordinate system for the current job:

1. From the main menu, select Files / Properties of current job - Coord.Sys.

2. Do one of the following:

♦

If the Key in parameters screen is selected, tap Next and then select Projection. Select an

♦ option from the Coordinates field. Complete the fields below as required.

If the Select coordinate system screen is selected, tap Next. Select an option from the

Coordinates field and then complete the fields below as required.

Trimble Geoid Models - WGS-84 versus Local Ellipsoid Based

Geoid Models

Caution - Geoid models are traditionally based on global WGS-84, and were previously always treated as global WGS-84 based geoid models even when they might have been based on local ellipsoid geoid models.

Trimble geoid models are now applied with respect to the interpolation method set in the geoid file, enabling both global WGS-84 and local ellipsoid based geoid models to be supported.

To avoid problems because of this change, consider the following items:

446

Note - The majority of jobs are created using coordinate systems with identity (0,0,0) transformations where the global and local ellipsoid are the same, and in this case, the enhancement of the Geoid model to support both global and local based interpolation models will have no impact.

•

All the North American geoid models have their interpolation method set to identify that they are local ellipsoid based models, even though they were previously treated as global WGS-84 based.

This means that if you are using datum transformation definitions that are not identity (0,0,0) transformations, elevations derived from the North American geoid models will change. This difference would normally have been corrected with a calibration, and now that the Geoid model is being interpolated differently, it is important to recalibrate jobs that fall into this category, as

• identified below.

All calibrations with the three following attributes must be recomputed to provide the same results:

♦ a vertical adjustment and

♦ a geoid model that is not built on an identity (0,0,0) transformation and

♦ an interpolation method that is local ellipsoid based

•

The existing EGM96 (Global) geoid model (ww15mgh.ggf) is updated to have its interpolation method changed to indicate that it is a global WGS-84 based model rather than a local ellipsoid based

• model. Update your geoid model to ensure it is interpolated correctly.

The existing OSU91A (Global) geoid model (OSU91A.ggf) is updated to have its interpolation method changed to indicate that it is a global WGS-84 based model rather than a local ellipsoid based model.

•

Update your geoid model to ensure it is interpolated correctly.

Because Minnesota and Wisconsin County Coordinate System definitions use customized local ellipsoids, you cannot use the standard local ellipsoid based North American Geoid models.

Therefore, new Geoid09 sub-grids have been created (G09-MN.ggf and G09-WI.ggf) and assigned as the default geoid models in the updated definitions for these systems. Upload these new global

WGS-84 based sub-grid geoid models to any controller that will be using these coordinate system

• definitions.

Any sub-gridded geoid model files that are uploaded to a controller inherit the same interpolation method as the geoid model they were created from. Update sub-grid models that were created from the existing EGM96 (Global) geoid model with sub-grid models created from the new EGM96

(Global) geoid model set up as a global WGS-84 based model.

A utility program GeoidModelConfig.exe is available on the Trimble Geoid Files web page

(www.trimble.com/tbc_ts.asp?Nav=Collection-71). Use this program to check the interpolation method in a

Trimble geoid model file; change it if necessary.

Note - When you select Step 2: Update Office Software, as part of the Trimble Survey Controller software installation process, all office products (for example, Trimble Business Center, Trimble Geomatics Office and

Trimble Pathfinder Office) are also updated with the new geodetic components. You must run the Update

Office Software step on all office computers so that both the field and office software use the same geodetic components.

Options Softkey

This softkey appears in only some screens. It allows you to change the configuration for the task being performed.

447

If you make changes using the Options softkey, they only apply to the current survey or calculation. The changes do not affect the current Survey Style or the job configuration.

Distances setting options

The computed area varies according to the Distance display setting. The following table shows the effect of the distance setting on the area calculated.

Distances setting

Ground

Computed area

At the average ground elevation

Ellipsoid

Grid

On the ellipsoid surface

Directly off the grid coordinates

Traverse Options

Use these options to specify how a traverse calculation is adjusted.

Field

Adjustment method

Option

Compass

Transit

What it does

Adjusts the traverse by distributing the errors in proportion to the distance between traverse points

Adjusts the traverse by distributing the errors in proportion to the northing and easting ordinates of the traverse points

Error distribution

Angular

Proportional to distance

Distributes the angular error among the angles in the traverse based on the sum of the inverses of the distances between traverse points

Equal proportions Distributes the angular error evenly among the angles in the traverse

None Does not distribute the angular error

Elevation

Proportional to distance

Distributes the elevation error in proportion to the distance between traverse points

Equal proportions Distributes the elevation error evenly among the traverse points

None Does not distribute the elevation error

Note - The Compass option is the same as the Bowditch method of adjustment.

For information about calculating and adjusting a traverse, see

Traverses.

Measure Display

Use the Measure display field to configure how the observations are displayed on the controller.

See the Conventional Instrument - Corrections table for a description of the measure display options and the

corrections that are applied.

Subdivide Pts Code

448

When you subdivide a line or an arc, a number of points are created. Use the Subdivide pts code field to specify the code that the new points will be allocated. Choose from the name or the code of the line or arc that is to be subdivided.

Coordinate View Settings

To change the Coordinate view setting (when reviewing a job) for a point that you want to view:

1. When reviewing the database, highlight the point record and tap Enter.

2. Tap Options and set the

Coordinate view

field as required.

If the coordinate value for a point is ?, one of the following situations may have occurred:

•

The point may be stored as a GNSS point but with the Coordinate view field set to Local or Grid and a datum transformation and projection not defined. To correct this, change the Coordinate view

• setting to WGS-84, define a datum transformation and/or projection, or calibrate the job.

The point may be stored as a

Grid (local)

point and with the Coordinate view field set to Grid, but a

• transformation has not been defined to convert the Grid (local) to a Grid.

The point may be stored as a polar vector from a point which has been deleted. To correct this, restore

• the point.

In a 2D survey, a projection may have been defined with the project height at null. To correct this, set the Project height to approximate the site elevation.

Projection Grids

Use a projection grid to handle projection types that are not directly supported by the Trimble coordinate system routines. A projection grid file stores local latitude and longitude values that correspond to regular northing/easting positions. Depending on the direction of the conversion, either projection or local latitude/longitude positions are interpolated from the grid data for points within the grid extents.

Use the Coordinate System manager to generate the defined projection grid (*.pjg) file.

For more information, refer to the Coordinate System Manager Help.

Use the Data Transfer utility or Microsoft ActiveSync technology to transfer the *.pjg file to the controller.

For more information, refer to the Trimble Survey Controller

File Transfer Help, Data Transfer Help or

Microsoft ActiveSync Help.

To use the projection grid in Trimble Survey Controller:

1. From the main menu, select Files / New job.

2. Enter the Job name.

3. In the Properties group, tap the Coord sys button.

4. Select Key in parameters, if required, tap Next.

5. In the Key in parameters dialog, select Projection.

449

6. In the Type field, select Projection grid from the drop-down list.

7. In the Projection grid file field, select the required grid file.

8.

If required, select the Use shift grid

check box.

9. Tap Accept twice, to return to the New job dialog.

10. In the New job dialog, tap Accept to save the new job.

Shift Grids

Initial projection coordinates are projections that are computed using specified projection routines. Some countries use shift grids to apply corrections to these coordinates. The corrections are generally used to fit the initial coordinates to local distortions in the survey framework, and so cannot be modeled by a simple transformation. You can apply a shift grid to any type of projection definition. Coordinate systems that use shift grids include the Netherlands RD zone, and the United Kingdom OS National Grid zones.

Note - The OS National Grid zones are now treated as a standard Transverse Mercator projection plus shift grid but they used to be handled as a special projection type with separate north and east grid files.

Use the Coordinate System manager to generate a shift grid (*.sgf) file. For more information, refer to the

Coordinate System Manager Help.

Use the Trimble Data Transfer utility or Microsoft ActiveSync technology to transfer the shift grid (*.sgf) file to the controller. The file is stored in [\Trimble Data].

For more information, refer to the Trimble Data Transfer Help or Microsoft ActiveSync Help.

Geoid files and Shift grid files are available on the web from: www.trimble.com/tsc_ts.asp?Nav=Collection-58928.

To apply a shift grid to a projection definition:

1. In the Projection dialog, select the Use shift grid check box.

2. In the Shift grid file field that appears, select the required file from the drop-down list.

450