compute active area of raster then create shapefile
mercierda
Global Mapper User
I have a bunch of NAIP Geotiff/MrSID files that contain arbitrary black border regions. Some images are rotated within the geotiff, and others contain a single county (of a random shape). I would like to know if there is a way to produce a polygon shapefile that defines the "active region" of the image, without having to manually digitize the polygon myself. Ideally this could be done based on a map catalog, or the batch processing portion of Global Mapper. I would like to generate one shapefile for each image. Is this possible?
Can any other tool already do this?
Thanks,
David
Can any other tool already do this?
Thanks,
David
Comments
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David,
There really isn't any way in Global Mapper to automatically identify the boundary of an irregular raster file. One possible trick I can think of to do this would be to export a file to an 8-bit grayscale BIL file from Global Mapper, then load that back in and specify that is is an elevation file. Then, use the File->Generate Contours menu command and generate a contour line at an "elevation" of 1. Assuming your border was black you should get a contour line around the outer edge of the valid area of the file as that would be a black border.
Note this would not be perfect if the source file was lossy so you had a bunch of near black areas or there were valid black colored areas near the edges.
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
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