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Tiling and area delimitation in raster images

chrisgrandinchrisgrandin Global Mapper UserPosts: 23Trusted User
edited February 2010 in Technical Support
Hi,

I try to do a transformation of ortophotos (tiff) using GM, it works fine for smaller areas. But if I have large areas I do get memory problems and GM crashes. Thus i tried to convert the ortho to ecw with low compression and then do the transformation. The problem with that, is that when I try to do the final cutting (with specific tilenaming), I would like to have the possibility to choose areas for the tiling and naming, and one area polygon to get rid of the compression artefacts that otherwise will occur at the edges of the irregular project area.

I don't seem to be able to do that, is there a way to make that?

Best regards,

Chris.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2010
    Chris,

    What version of Global Mapper are you using and what are the errors that you are seeing?

    For the tiling, what you can do is select the area features that you want to tile your export to with the Digitizer Tool, then when you do the export, go to the Gridding tab and select the option to grid to the selected area features. This will do a separate export for each selected area feature.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • chrisgrandinchrisgrandin Global Mapper User Posts: 23Trusted User
    edited February 2010
    Hi and thanks for your time,

    I use GlobalMapper 11.

    Sorry for bad explanation of the problem.

    If I convert tiff files to ecw that have an original background color that is for example white, I will get artefacts at the edges of the original background. Since many customers have systems that sets white as background color and treat it as transparent, there will be ugly edges at the original boundary between the white background and the area.

    My idea was that when I am to cut the final tiles for the delivery and cut it in predefined tiles (I use the digitizer tool and select the tiles before export as normal), I would have the chance to select another polygon that only purpose is to define the export bounds.

    That way I would be able to transform large areas using ecw compressed images, and get rid of the compression artefacts caused by the ecw conversion.

    As I understand it, if I use the digitizer tool to select ALL area features I have no possibility to choose which of those to use for the tiling (gridding) and which to use for the export bound.

    Best regards

    Chris
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited February 2010
    Chris,

    I think what you might want to do here is generate an ECW file with the option checked to make background pixels transparent. Then any border pixels outside the valid area of the source TIFF files will be marked as transparent in the generated ECW file. Any application that supports ECW files with an alpha channel should automatically treat all of those regions as transprent, so you won't get the fuzzy edge.

    Another thing you might want to know about is the ability to set a crop polygon for loaded layers. You can do this by selecting the polygon to crop a layer to, then going to the Cropping tab of the Options dialog for the layer and selecting to crop the layer to the polygon. Then that layer will be cropped for display and export and you can later use a completely separate polygon to crop the actual export.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • STHSTH Global Mapper User Posts: 434Trusted User
    edited February 2010
    You can do the following (hope this is accurate enough):

    1. Create a MapCatalogue with all the ECWs
    2. Load the clipping area (not the tiles) and select the area.
    3. Click on the mapcatalogue in the "Layers view" and choose Options
    4. Choose raster display - settings and Crop to currently selected polygon

    5. Load the final tiles and select only these (you can now unload the clipping area you selected before)
    6. Export as usual and in the Gridding tab use the "Selected areas" as clipping to get one file per tile.

    Hope this helps
  • chrisgrandinchrisgrandin Global Mapper User Posts: 23Trusted User
    edited February 2010
    Thanks alot for your answers Mike and Sigbjorn! I will test your ways at once!

    Best regards
    Chris
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