GeoTiff unrectified

jrejre Global Mapper UserPosts: 14Trusted User
edited October 2009 in Technical Support
Hello,

I've a GeoTiff raster. This GeoTiff have got several GCPs or ModelTiepointTag. But it haven't got rectification information or ModelPxelScaleTag.

So it couldn't be projected with any software. But GlobalMapper display this raster as if it havec got recitfication information.

My question is how GlobalMapper do displaying this raster. What operation, what options in rectification are used ?


Thanks,

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2009
    If a GeoTIFF provides at least 2 control points rather than a model tie point and pixel scale then Global Mapper will rectify the GeoTIFF using the control points. The rectification method use will depend on how many control points are available (i.e. linear for 2, affine for 3, polynomial for 4, and triangulated for 5 or more).

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • jrejre Global Mapper User Posts: 14Trusted User
    edited October 2009
    Thanks,

    Fortunately, my GCPs are well made.

    But if for one reason there aren't in a good configuration, for a sample only on one side of the raster, can I control the rectification method ?

    Or I must extract the GCPs and using "rectify imagery" tool ?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2009
    You can right-click on the layer in the Control Center after loading it and select the option to modify the layer position. This will bring up the rectification dialog with the control points and allow you to modify the control points and the rectification method to fit your needs.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • jrejre Global Mapper User Posts: 14Trusted User
    edited October 2009
    OOh,

    I have never used enough right-click on the Control Center... :(


    I have a strange behavior with rectification tool, so I follow this thread : With my set of points, when I confirm the rectification method, error values for each point are changing. Why have not I got the same results all the time ?


    Best regards and thank for your so quick responses.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2009
    Which rectification method are you changing to and what is the magnitude of the errors that you are seeing? If you use a rectification method where there are more points than needed you will likely see some error as that rectification method can't perfectly fit the available number of points, so a least-squares fit solution is used.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • jrejre Global Mapper User Posts: 14Trusted User
    edited October 2009
    I'm sorry,

    I don't explain very well the situation. When I have written "I confirm the rectification method", I see that the method is automatic and so I click on automatic. I don't made any change. I juste confirm actual method.

    That I have error, it's normal, and the aim of georeferencing may to not be the lesser errors.



    I have performed another tests. And I understand. This changement is only with triangulation method, or automatic (but it's the same, because I have here 15 points). But I have not noticed it, but my points are regularly spaced. So for triangulation method, there 2 solution to make triangle. So it isn't so strange that I have changes when I confirm my rectification options.


    Thanks for your assistance.
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