Georeferencing problems

SalamSalam Global Mapper UserPosts: 2
I am rectifying some maps with UTM32/33 projections. First I entered 4 gcp points but the rectified maps had a lot of distortion. Then I rectified them using 50 gcp points but still there is a lot of distortion. I am using "Automatic" as the rectification method and "Bilinear Interpolation" as the Resampling method. Does adding more points decrease the distortion or not?! Do I have to change the rectification method?

Also some times after entering more gcp points the Error of some other points increses! What do I have to do with those points? Do I have to delete the points with large errors? what is considered as a large error? Sometimes adding more points around a point with large error decreases its error but sometimes the errors just increase!

Does anybody have any suggestion?
Any suggestion is really appreciated.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited May 2009
    What version of Global Mapper are you using? With the latest release you should always have an error of 0 (or very near 0) when using the 'Automatic' rectification method. There were some bugs in older releases that would cause this to not be the case.

    When you do see errors, they refer to how many pixels off the rectified location of a control point is from the original. Usually values less than 2 or so are fine, larger than that and they begin to be a problem.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • SalamSalam Global Mapper User Posts: 2
    edited May 2009
    Many thanks for your response. I am using GM v10.00. But I still get a lot of errors while entering gcps!! I have errors even greater than 27!!

    Do you know what is causing these errors? Is that why maps are distroted.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited May 2009
    Can you try downloading and installing v10.02 from http://www.globalmapper.com/global_mapper10_setup.exe and see if that fixes the problems?

    If not can you save a workspace file and post that so that I can take a look?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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