Global Mapper v25.0

MapInfo TAB files

PatG
PatG Global Mapper UserTrusted User
edited April 2009 in Bug Report
We have noticed that creating MapInfo TAB files in GlobalMapper causes a half pixel shift in the raster imagery. This appears to be because a TAB created by MapInfo uses the pixel center as the origin and GlobalMapper uses the top left corner as its origin. The resulting TAB files are different locations when viewing the imagery in other software if the TAB files have been created externally.

Can you advise if this is a bug or deliberate?

Comments

  • global_mapper
    global_mapper Administrator
    edited April 2009
    Pat,

    What version of Global Mapper are you using and what format are you exporting to?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatG
    PatG Global Mapper User Trusted User
    edited April 2009
    Mike,
    We are using BM ver 9.03 and we use the batch convert option with input of GeoTif, output Geotif or input ECW, output ECW and export of Metadata files only. The input files may not have georef data in the header but will always have world files associated with them (ers,tfw,eww etc..). We also use a plugin for MapInfo called "worldreg" to generate TAB files. The differences between these outputs is causing the issue.
  • global_mapper
    global_mapper Administrator
    edited April 2009
    Pat,

    Can you provide an example TFW file and the TAB file generated by the other tool so that I can take a look? I looked through the GDAL library's handling of .tab files and they seem to interpret them the same way as Global Mapper does, and is the way the is the most obvious, but it is possible that both Global Mapper and GDAL are doing things wrong.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatG
    PatG Global Mapper User Trusted User
    edited April 2009
    Mike,
    Please find attached a TFW and TAB file made using MapInfo as requested. I tried to attach the 12Mb relevant image but this crashed a couple of times...

    Let me know if you need more info..
  • global_mapper
    global_mapper Administrator
    edited April 2009
    Pat,

    I wonder if there is a chance that your other tool for converting the TFW files to TAB files is misinterpreting the TFW coordinates as being cell corners rather than cell centers, resulting in the TAB files being different rather than this being a problem with how the TAB file coordinates are interpreted. Since I can't find any reference that specifically says that TAB file coordinate should be interpreted as offset one half pixel from the specified pixel coordinates in the TAB file and the other widely used software library that I could check (GDAL) interprets the TAB coordinates the same way that Global Mapper does, I'm inclined to think the problem may not be in the TAB file coordinate interpretation but in the TFW coordinate interpretation of the other software.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • PatG
    PatG Global Mapper User Trusted User
    edited April 2009
    Mike,
    I can't rule out this possibility but I also have no way of checking. We will have to ensure we don't mix the two methods when generating our world files in future. This should avoid the issue but doesn't get to the bottom of it. many thanks for looking into it though...