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:
- Click Home | New Map | Base | Base, select the BLN file and click Open. The BLN file is imported as a base map.
- In the Contents window, expand the Base layer group and select a polygon in the BLN file.
- Click Features | Edit Features | Reshape.
- Reshape the polygon.|
- Press ESC on the keyboard when you are done reshaping the polygon.
- The edited BLN polygon can now be used to assign NoData values to the grid by following these steps:
- Click Grids | Edit | Assign NoData.
- 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.
- Click in the NoData Polygon Boundary field and select the Base layer containing the BLN polygon.
- Toggle NoData Outside or the desired no data option.
- Uncheck the box next to Add grid as layer to, if desired, and then click OK.
- To save the edited BLN polygon for later use:
- Uncheck the boxes next to each of the four axes in the Contents window.
- Click File | Export.
- 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.
- In the Export Options dialog, set the Scaling source to your Map on the Scaling tab.
- On the BLN Options page, choose whether to assign no data Inside or Outside of your polygon in the NoData areas section.
- Click OK to create the file.
Updated November 13, 2018