Global Mapper v25.0

compute active area of raster then create shapefile

mercierda
mercierda Global Mapper User
edited September 2009 in Vector Data
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

Comments

  • global_mapper
    global_mapper Administrator
    edited September 2009
    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