How can I reshape a BLN file and use the modified file for blanking in Surfer?

In Surfer, you can load a BLN file as a base map, reshape the polygon and then use the updated BLN file to assign a NoData value to areas inside or outside the polygon. To do this:

  1. Click Home | New Map | Base | Base, select the BLN file and click Open. The BLN file is imported as a base map.
  2. In the Contents window, expand the Base layer group and select a polygon in the BLN file.
  3. Click Features | Edit Features | Reshape.
  4. Reshape the polygon.|
  5. Press ESC on the keyboard when you are done reshaping the polygon.
  6. The edited BLN polygon can now be used to assign NoData values to the grid by following these steps:
    1. Click Grids | Edit | Assign NoData.
    2. In the Assign NoData to Grid dialog, click in the Input Grid field and select the map layer containing the desired grid or click Browse to select a grid file.
    3. Click in the NoData Polygon Boundary field and select the Base layer containing the BLN polygon.
    4. Toggle NoData Outside or the desired no data option.
    5. Uncheck the box next to Add grid as layer to, if desired, and then click OK.
  1. To save the edited BLN polygon for later use:
    1. Uncheck the boxes next to each of the four axes in the Contents window.
    2. Click File | Export. 
    3. In the Export dialog, set the Save as type to BLN Golden Software Blanking (*.bln), give your file a name, and verify Show options dialog is checked. Click Save.
    4. In the Export Options dialog, set the Scaling source to your Map on the Scaling tab.
    5. On the BLN Options page, choose whether to assign no data Inside or Outside of your polygon in the NoData areas section.
    6. Click OK to create the file.


Updated November 13, 2018

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