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I would like to display a Geosoft grid (*.grd) in ArcMap using a custom Geosoft colour ramp created in Oasis montaj/Target.


Geosoft grid files (*.grd) can be opened directly in ArcMap if you have the Geosoft Extension for ArcGIS or the Geosoft Plug-in for ArcGIS is installed.

To create a custom colour ramp in Oasis montaj/Target:

  1. Double-click a displayed grid in the View/Group Manager Tool to open the Colour Tool.
  2. Set the colour scale as desired using the Transform options or by manually adjusting the colour scale.
  3. Once the colour ramp is set, click Save to File (icon displaying a floppy disc).
  4. Set the ‘Save as type’ to Colour Zones (*.zon).
    This will create an ASCII file that can be edited in a text editor.
  5. Save the file to:
    64-bit computers – C:\Program Files\Geosoft\Desktop Applications\tbl
    32-bit computers –  C:\Program Files (x86)\Geosoft\Desktop Applications\tb
To display the Geosoft Grid in ArcMap:
  • Use Add Data from the Standard Toolbar > browse to and select the grid file > Add.

To apply a customer colour ramp to the grid:

  1. In the Table of Contents right-click the layer > Properties.
    The Layer Properties dialog will open.
  2. Select the Symbology tab.
  3. Right-click the Color Ramp and clear the Graphic View check mark.
  4. From the Color Ramp droplist, locate and select the custom colour ramp you saved to the …ArcGIS\tbl\ folder.
    Colour ramps created in Oasis montaj or Target will automatically be given a “Geosoft” prefix.  For example, if you named your zone file customgrav.zon, you will see it listed as ‘Geosoft customgrav” in the Color Ramp droplist.
  5. Under Stretch, set the Type to Histogram Equalize.
  6. Click the Display tab and set ‘Resample during display using’ to Bilinear Interpolation.


In ArcGIS the colour ranges are not honoured if using a *.zon file.  These data ranges do not carry over to ArcGIS because the zone file is turned into a colour ramp and the settings in the Symbology Options determine how that color ramp is applied.

In order to honour the data ranges and colours, make a map in Oasis montaj or Target and import it into ArcMap using the “Import Geosoft Map” in the Geosoft Extensions toolbar. This will give the exact colour distribution which will render the same as it does in Oasis montaj or Target.

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