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  1. #1
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    Default Image Rectifier: Raster Image in "Zoomed View" window GCP not being placed correctly

    This is not a snapping issue. I have ALT clicked to no avail. Plus there is no vector data in the Zoom View window.

    Basically when I try to add a GCP to the ZOOMED VIEW window the point is placed about 10 pixels away. There is no vector present. This is a raster image.

    This is how I got to this point.
    Loaded shape-files (lat/long).
    Loaded a dumb TIF and choose to rectify it.
    I used the shape-files to pick the GCPs.
    Changed the projection to match the raster and saved PRJ file.
    Selected triangulation as method.
    Saved the GCP file (just in case).
    Clicked OK in the Image Rectifier and viewed in the main window.
    Saved the workspace (which I see saves the GCPs inside the GMW file).
    Opened the GMW workspace next day.
    Opened the Overlay Control Center and right-clicked on the TIF layer to Modify Layer Position/reprojection.

    Added a few more GCPs. It was after a few iterations of this that I noticed that despite the triangulation method some GCPs seemed to be ignored as the raster and vector did not match at that point (PROBLEM 1). When I went back into the Rectifier Tool I had to UPDATE the points as they had moved off the GCPs slightly (PROBLEM 2). Also, when clicking in the Zoomed View (TIFF) the point would be offset about 10 pixels from the cursor axis (PROBLEM 3).

    Note: I never exported the TIF to a file. I left it in its original form. Once I am happy with the rectification I will export it. But wondering if the constant "Modify Layer Position" is destructive or have I run into a limitation with the projection algorithm? It is Lambert Conic.

    Any ideas?

  2. #2
    Administrator
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    Default

    That is strange, what version of Global Mapper are you using? You could be seeing some old bugs with rectification that have since been fixed.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com

  3. #3
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    Default

    11.02 I think. I am not at my PC right now to verify but it was only about 1-2 months old.

  4. #4
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    When you get back to your PC can you first try getting the latest v11 build to see if that makes any difference? I have placed a new build at http://www.globalmapper.com/global_mapper11.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v11.xx installation folder to give it a try. If you are using the 64-bit v11 version there is a new build at http://www.globalmapper.com/global_mapper11_64bit.zip .

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com

  5. #5
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    Thumbs up

    Quote Originally Posted by global_mapper View Post
    When you get back to your PC can you first try getting the latest v11 build to see if that makes any difference?
    Thanks Mike. I did in fact have 11.02 (June build). I have downloaded the September EXE and DLLs. The DLLs seemed to be identical (time stamp differed by a few seconds on a few of them.

    Starting the test.

    IT WORKS NOW. This did correct all 3 issues I was having. One thing I noticed is that the triangulation now seems to be using a linear fit versus an inverse square weighted method.

    A big thanks.
    Last edited by Jake; 09-03-2010 at 02:04 PM. Reason: fixed quote

  6. #6
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    Default

    linear fit versus an inverse square weighted method
    Actually I take that back. The inverse square weighted method would not have produced the results I was seeing.

  7. #7
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    The triangulated rectification should work the same as it always has, so I'm not sure why you are seeing a difference. The method is also called piecewise affine as a 3-point affine transformation is done inside each triangle.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com

  8. #8
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    Default

    Well the problems have re-surfaced. Some of the points are moving 20 pixels or about 350m on the ground).

    Thanks for the extra information on the method.
    Last edited by Jake; 09-03-2010 at 05:11 PM.

  9. #9
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    Default

    I have added a snapshot to illustrate one of the issues I am having. Method is triangulation yet GCPs do not line up after performing the triangulation. As you can see the vector and raster data does not match at the GCPs. I would expect there to be variations/tearing along the triangle edges but not at GCP. I can send you the source files if needed.

    PS: Forum re-sampled from a 1.2 Mpixel 27KB PNG file to an 18KB jpeg when I uploaded it.
    Attached Thumbnails Attached Thumbnails Image Rectifier: Raster Image in "Zoomed View" window GCP not being placed correctly-gm_triangulation.jpg  
    Last edited by Jake; 09-03-2010 at 05:43 PM.

  10. #10
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    Default

    PSS: Just manually checked the pixel coordinates in another software package and they are the correct values (1 pixels). The problem is the ZOOMED VIEW plots them incorrectly. So since I am basing my positions on the slightly shifted ZOOM VIEW I am getting slightly shifted results. The shift does not seem to be consistent either.

 

 
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