Oasis montaj How-To Guide
3D Gridding - Create Voxels using 3D Gridding Methods
The software described in this manual is furnished under license and may only be used or copied in
accordance with the terms of the license.
Manual release date: April-17-12.
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Create Voxels using 3D Gridding Methods
You can create a Voxel using the 3D Gridding submenu, located on the 3D menu. A "voxel" is short for
"volume pixel", the smallest distinguishable box-shaped element of a three-dimensional image. A Voxel
is the 3D conceptual counterpart of the 2D pixel.
The 3D Gridding submenu offers 3 different gridding algorithms, each with a different focus:
The Kriging method best suits clustered data occurring in a region with otherwise sparse data
distribution, such as geochemistry data.
The Direct Gridding method on the other hand should be used to grid data uniformly and densely
sampled throughout the region, such as GPR or seismic data.
Lastly, with gridding data collected along specific directions - such as borehole data - Inverse
Distance Weighted Gridding will be most suitable.
3D Menu
Figure 1: 3D Gridding menu system
The data to be gridded must have defined X, Y and Z coordinates. The 3 dimensional coordinate system
will locate the data in space. The Z axis is interpreted as positive up. The 3D workflow includes tools for
creating, displaying and processing voxels. The 3D Viewer allows for visual inspection of voxels and
comes with a rich set of 3D viewing tools.
Voxels 3D Gridding
Creating a Voxel Model using the Kriging method
When applying 3D gridding, halving the cell size reduces both the file size and processing time by
a factor of 8 (2 3).
Creating a Voxel Model using the Kriging method
From the 3D Gridding menu, select the Kriging option to perform a statistical-based 3D gridding. The
input data must be supplied in a Geosoft database (GDB file). The output will be a voxel model within the
confines of the data extent.
To Create a 3D Voxel model using Kriging:
1. Open a Geosoft data database containing X, Y, Z and the data channel you would like to grid. If
the coordinate system is not completely defined, a message will pop up and you will not be able
to continue until the corrective action is taken.
2. On the 3D menu, select 3D Gridding | Kriging. The 3D Kriging dialog appears.
Figure 2: 3D Kriging Gridding dialog
If a database is not already open you will be prompted to open one.
3. From the drop-down list, select the Channel to grid. The first time through the process, the default
Output voxel file name will the set to the provided channel name. The subsequent invocations of
this tool will remember the user specified file name. You can rename the output voxel file or
accept the default name.
4. Specify the Cell size. If you do not have a preset cell size, click the Calculator
button to
obtain a reasonable cell size based on the extents of your data. The cell size is calculated for a
single cube, assuming the volume is divided into 10000 individual cubes. The value is then
rounded down to give a more satisfactory value.
We recommend that your first attempt at gridding be using the remainder defaults. After
inspecting the outcome however you may decide to modify defaults such as the Blanking
Distance to fill in the gaps, modify the Z cell increment, or generate the output on a
logarithmic scale.
Additionally you can customize the variogram to best suit your data.
5. When you are satisfied with your selections click OK. The Voxel is created and displayed in the
Voxel Viewer. An example is shown below:
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Voxels 3D Gridding
Creating a Voxel Model using the Direct Gridding method
Figure 3: 3D Voxel produced with 3D Kriging Gridding method
The Voxel Viewer provides additional viewing tools.
Creating a Voxel Model using the Direct Gridding method
To Create a 3D Voxel model using Direct gridding:
1. Open a Geosoft data database containing X, Y, Z and the array data channel to grid. If the
coordinate system is not completely defined, a message will pop up and you will not be able to
continue.
2. On the 3D menu, select 3D Gridding | Direct Gridding. The 3D Direct Gridding dialog appears.
.
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Voxels 3D Gridding
Creating a Voxel Model using the Direct Gridding method
Figure 4: 3D Direct Gridding dialog
If a database is not already open you will be prompted to open one.
3. From the drop-down list, select the array Channel to grid. Only array channels are eligible to be
gridded. The first time through the process, the default Output voxel file name will the set to a
combination of the current database and provided channel name. The subsequent invocations of
this tool will remember the user specified file name. You can rename the output voxel file or
accept the default name.
4. Specify the Cell size. If you do not have a preset cell size, click the Calculator
button, to
obtain a reasonable cell size based on the extents of your data. The cell size is calculated for a
single cube, assuming the volume is divided into 10000 individual cubes. The value is then
rounded down to give a more satisfactory value.
5. The default vertical Z cell size is set to the same value as the horizontal cell. If this value is not
reflecting the desired resolution, modify it accordingly.
6. When you are satisfied with your selections click OK. The Voxel is created and displayed in the
Voxel Viewer. An example is shown below.
Figure 5: Direct Gridding of GPR data. Data courtesy of UIT
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Voxels 3D Gridding
Creating a Voxel Model using the Inverse Distance Weighted (IDW) Gridding method
Creating a Voxel Model using the Inverse Distance Weighted (IDW) Gridding
method
To Create a 3D Voxel model using Inverse Distance Weighted Gridding:
1. Open a Geosoft data database containing X, Y, Z and the array data channel to grid. If the
coordinate system is not completely defined, a message will pop up and you will not be able to
continue.
2. On the 3D menu, select 3D Gridding | Inverse Distance Weighted Gridding. The 3D Inverse
Distance Weighted Gridding dialog appears.
.
Figure 6: 3D Inverse Distance Weighted Gridding dialog
If a database is not already open you will be prompted to open one.
3. From the drop-down list, select the array Channel to grid. The first time through the process, the
default Output voxel file name will the set to a combination of the current database and provided
channel name. The subsequent invocations of this tool will remember the user specified file
name. You can rename the output voxel file or accept the default name.
4. Specify the Cell size. If you do not have a preset cell size, click the Calculator
obtain a reasonable cell size based on the extents of your data.
button, to
5. When you are satisfied with your selections click OK. The Voxel is created and displayed in the
Voxel Viewer. An example is shown below.
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Oasis montaj How-To Guide | 5
Voxels 3D Gridding
Creating a Voxel Model using the Inverse Distance Weighted (IDW) Gridding method
Figure 7: Inverse Distance Weighted Gridding of Borehole data
We recommend that your first attempt at gridding be using the remainder defaults. After
inspecting the outcome however you may decide to modify defaults such as the
Weighting power & slope to alter the degree of influence of contributing data points relative
to their distance , or the Blanking Distance to fill in the gaps, or generate the output on
logarithmic scale.
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