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Undo "Specify Projection" in Batch Conversion

aerial21aerial21 Global Mapper UserPosts: 4
edited March 2012 in Raster Data
I converted thousands of TIF (aerial images without any georeference) to JPEG2000 with "Batch Convert”. Unfortunately we set the option "Specify Projection" and the JPEG2000 images got distorted.
At the free areas in the back of a JPEG2000 image you can now see the background color of global mapper. The images are distorted and got additional informations (pixels of background color).
How can we undo the projection settings / the distortion (We don’t have the original TIF files any more)?
The Projection we used: Gauss Krueger Germany (3 degree) Zone 4.
Thanks for your help

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2012
    You could do a batch convert back to the original projection which should undo the projection, but since JPEG2000 is lossy you will have lost some information. You might convert back to GeoTIFF since at least you wouldn't be losing any more information that way, but you would of course have much larger files.

    As for the borders, once you've got the distortion un-done, load those into Global Mapper and go to the Options dialog for the layer and first try using transparency to set the background color transparent and also specify to make similar colors transparent. Since the JPEG2000 format was lossy your background area will not be all exactly the same color but very similar. The best option really would be to go to the Cropping tab and crop your file to the actual data bounds. This will work perfectly and can easily be setup if the tile data is along some straight boundary, either in native coordinates or lat/lon. Another option would be if you have area features describing the coverage of the tiles available you could crop to those.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • aerial21aerial21 Global Mapper User Posts: 4
    edited February 2012
    Thanks for your reply.
    That’s the point: I have no original projection because the aerial images are without any georeference.
    As for the borders: if the undo projection works fine, there shouldn’t be any background pixel left.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2012
    Oh I see you basically geo-rectified a bunch of non-referenced images to some projection and want to back to the original unreferenced images? That I'm afraid is not really possible as the transformation based on the control points is basically "baked-in" to the new images and isn't just a transformation of the raw images based on those control points on the fly, or at least once you've exported that is the case. I can't really think of any way to "un-rectify" the images to get back to the originals, that was lost in the translation so if you don't have the originals around anywhere there really isn't a way to get back to them from the end product.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • aerial21aerial21 Global Mapper User Posts: 4
    edited February 2012
    In order to make a transformation basically, you have to select the input and output projection.
    In my case, I (unfortunately) selecteted an output projection. No input projection (there is no projection). I didn’t collect or measure any control points on my own.
    My question is: What did global mapper do in this case? What projection does global mapper assume, if there is no projection at all? Global mapper definitely assumes an input projection in order to do the transformation.
    All the images have been transformed the same way. How? How can I undo this (perhaps with another software)?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2012
    The transformation wouldn't make sense unless the files had some type of input projection. You can't reproject from nothing to something. Were you asked for a projection when loading the files? Did you have to manually rectify these files in order to get them positioned? That's what I had thought you had done? I suppose you could have specified to use the "default position" for all files that don't have position information, then each one would have been treated as having the NW corner at 0,0 lat/lon and used a projection of Geographic/WGS84/Arc Seconds (note NOT Arc Degrees, Arc Seconds is used so you can easily see pixel coordinates but not have invalid coordinates off the earth). You could try reprojecting to that projection and see if that works.

    Thanks,

    Mike
  • aerial21aerial21 Global Mapper User Posts: 4
    edited March 2012
    I only used "Batch Convert" for converting. I wasn't asked there for a projection. In fact I didn't put the images in the viewer. I also did no rectifying before converting.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2012
    Every file in Global Mapper has to have a projection, and if one cannot be determined a default one is used (at least during batch conversion, in the normal UI you are asked about rectifying). So long as you didn't select a different output projection when batch converting no reprojection would happen, but it sounds like maybe you selected a specify projection to output to, which would cause the default selected position/projection to be reprojected to the new projection that you selected.

    You can try doing a batch conversion back to a projection of Geographic (lat/lon) and see if that gets you back close to your originals.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
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