GeoTiff unrectified
jre
Global Mapper UserTrusted User
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,
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
-
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 -
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 ? -
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 -
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. -
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 -
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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