How can I convert the coordinate system of a grid file (e.g. from Lat/Long into feet or meters) using Surfer?

There are times when you may need to change the coordinate system of the grid file itself, instead of just a map, for use in Surfer. This may be the case when performing grid operations such as Grid Volume or Grid Calculus.
This is often the case when the Z value is in feet or meters, but the XY coordinates are in Lat/Lon. When your XY units are lat/long, volume calculations can result in a volume of just a few thousandths of a single unit (since the volume results are in units of lat*long*feet (or meters), which is X*Y*Z) and slope analysis can result in all slopes being near 90°. To get meaningful volume or calculus results, the units on the X and Y axes need to be in linear units (feet, meters, etc) and the Z units must be known.
To convert a grid to a new coordinate system in Surfer, follow the steps below.
  1. Click Grids | Edit | Project.
  2. In the Grid Project dialog, click Browse, select your grid file, and click Open.
  3. Click Set in the Input Grid section.
  4. In the Assign Coordinate System dialog, select the coordinate system of the original data and click OK.
  5. Click Set in the Output Grid section.
  6. In the Assign Coordinate System dialog, select the coordinate system you want the grid converted to and click OK.
  7. Click OK in the Grid Project dialog to create the new grid file.


In Surfer 13 and earlier versions, there is not a direct way to convert the grid file from latitude and longitude coordinates to a system whose native unit is feet or meters; however you can use the Surfer worksheet for this task:

  1. First identify the Z data unit.  If the Z units are meters, then the lat/long coordinates can be converted to meters also (e.g. UTM).  If feet, you can convert to a system where the units are in feet (e.g. State Plane in the US).
  2. Click Grid | Convert, select the grid file and click Open.
  3. Choose to save the grid in an DAT XYZ (*dat) file format and click Save.
  4. Click File | Open, select the DAT file and click Open. It will open in the Surfer worksheet.
  5. Click Data | New Projected Coordinates.
  6. Set the source data columns, X: Column A and Y: Column B.
  7. Click the (...) button under Source Coordinate Systems.
    1. In the Assign Coordinate System dialog expand Predefined | Geographic (lat/lon), and select the appropriate datum for the data. The most common datum for lat/long coordinates is World Geodetic System 1984.
    2. Click OK.
  1. Click the (...) button under Target Coordinate Systems.
    1. In the Assign Coordinate System dialog change the coordinate system to either UTM or State Plane 1983 under Projected Systems.  Here you will need to either know the UTM zone or the State Plane zone. 
    2. Click OK.
  1. Click OK and the coordinates are converted into the target columns.
  2. Click File | Save and File | Close.
  3. Click Grid | Data, select the data file and click Open. In the Grid Data dialog:
    1. Make sure the X and Y column are set to the new columns of meters or feet.
    2. Select the Nearest Neighbor gridding method.
    3. Use the same grid resolution (same # of Nodes) as the original grid file.
  1. Click OK and the new grid is created. Use this grid for volume calculations or for whatever other purpose you wish.

Updated October 3, 2017


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