How to georeference an ECW file

vagtazohalottkemvagtazohalottkem Global Mapper UserPosts: 15Trusted User
edited May 2012 in Raster Data
Hi Global Mapper Community! I have a big ecw file, around 1 gb. It's exported from a database. I georeferenced again with ArcGis, collected about 200 gcps. I selected in ArcGis the spline interpolation.ArcMap is soooooo sloow, and i wanted to use my ""wonder-weapon" the Global Mapper. I loaded the file, rectify and i loaded the GCP file. This is from ArcMap, formatted a bit, to be readable for GM. The problem is: the file georeferenced, and in the GCP file there are coordinate pairs: XY and newXY, the original xy pairs are based on the cordinate system, stored in the ecw, and the new XYs are in the stored coordinate system too. If i see the GM rectify window, i see the imported GCPs in the third window section, but i don't see in the first or in the second. If i click on OK, the GM working a bit, and rotating the file and warping to a weird place in the virtual space. The problem is, can i use GCP file, which contains coordinate pairs in the ""georeference coordinate system"? I saw an example GCP file, which contains coordinate pars, the first two is the image xy and the second two is the georeference coord system coordinates. Any idea? BEst regards, Steve

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2012
    Steve,

    You can use that file, just not in the rectification window since you aren't mapping the pixel coordinates of the ECW to some coordinate system but instead transforming within the same coordinate system. To do this, right-click on the layer in the Control Center and select the option to shift the layer (near the top of right-click menu). You can then select to transform based on a file and then use your control point file.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • vagtazohalottkemvagtazohalottkem Global Mapper User Posts: 15Trusted User
    edited May 2012
    Hi Mike! I think it's a very good solution. I'm opened the shift-file and now GM is working on the exported file. But, these shifting parameters in ArcMap was ""spline" georef method GCPs. I mean, the original, georeferenced file was a bit ""shifted" by these points. In this solution, which method was used by this shift command? I checked some parts of the shifted image, and seems very good. I only want to know, is there any option to change parameters, methods of shifting?

    Best regards, Steve
    Steve,

    You can use that file, just not in the rectification window since you aren't mapping the pixel coordinates of the ECW to some coordinate system but instead transforming within the same coordinate system. To do this, right-click on the layer in the Control Center and select the option to shift the layer (near the top of right-click menu). You can then select to transform based on a file and then use your control point file.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited May 2012
    Steve,

    The results will be the same calculation as the "automatic" rectification does, just with different types of numbers. So for 5 or more points you will do a piecewise-affine (trianguled) transformation, which basically forms a Delaunay triangulation of the input points and then transforms a point by finding the input triangle it is in, then transforming that to the associated output triangle. This should exactly maintain your control points.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • vagtazohalottkemvagtazohalottkem Global Mapper User Posts: 15Trusted User
    edited May 2012
    Hi Mike!

    I think i have no more questions about it. The GM created a new ecw file from the starting file, in around 57 minutes...OrkMap freezed, and worked for 5 hours, and at the end made a full black, unusable file.
    I see a little difference between OrkMaps "spline" georef and GM's triangulation, but i'm working with old, handmade maps, so the difference doesn't matter.

    Thank you very much for the fast help!
    :cool:
    BEst regards,
    Steve

    Steve,

    The results will be the same calculation as the "automatic" rectification does, just with different types of numbers. So for 5 or more points you will do a piecewise-affine (trianguled) transformation, which basically forms a Delaunay triangulation of the input points and then transforms a point by finding the input triangle it is in, then transforming that to the associated output triangle. This should exactly maintain your control points.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
Sign In or Register to comment.