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How can I find the maximum slope within an area around a point in Surfer?

To find the highest slope within a area around a point, blank the grid to the desired radius, and view the grid info.

  1. Create the slope grid file.
    1. Click Grids | Calculate | Calculus. 
    2. In the Grid Calculus dialog, select a map using your grid file from the Input Grid dropdown list, or click the Browse button to navigate to and select your grid file.
    3. Choose Terrain Modeling | Terrain Slope.
    4. Change the Output Grid name and location, if desired.
    5. Uncheck the box next to Add grid as layer to.
    6. Click OK and the grid is created. (Click OK in the Surfer dialog telling you the grid was created.)
  2. Now create a BLN defining the area you want to calculate the maximum slope in. Please see this article for instructions to create a BLN file. If you have Surfer 14, you can easily create the circular area around a point in a base layer using the Features | New Features | Buffer command. 
  3. Click the Grids | Edit | Blank command.
  4. In the Grid Blank dialog:
    1. Select a map using your grid file from the Input Grid dropdown list, or click the Browse button to navigate to and select your grid file.
    2. Select a map using your BLN file from the Blanking Polygon Boundary dropdown list, or click the Browse button to navigate to and select your BLN file.
    3. Toggle the appropriate option for the direction of blanking (inside, outside, or mixed).
    4.  In the Output Grid field, enter a name for the new blanked grid.
    5. Uncheck Add grid as layer to.
    6. Click OK.
  5. Click the Grids | Info | Grid Info command.
  6. Select the blanked grid file created above and click Open
  7. In the Grid Information report, scroll down to the Univariate Grid Statistics section. The Maximum is the maximum value in the non-blanked portion of the grid.

 

For additional statistics about the slope in this radius, you can:

  1. Convert the GRD file to a DAT file (Grids | Edit | Convert).
  2. Open the DAT file in the worksheet (File | Open).
  3. Sort on Column C (Data | Data | Sort).
  4. Remove the rows with NoData values (1.70141e+038).
  5. Select the desired data cells.
  6. Click the Data | Data | Statistics command.
  7. Check the boxes next to the desired statistics.
  8. Click OK to calculate those statistics for the selected cells.

 

Updated January 9, 2017

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