Projection issues - Global Mapper 11

TrustPowerTrustPower Global Mapper UserPosts: 4
edited April 2010 in Technical Support
Hi I am having problems with New Zealand Map Grid Projection - I have shapefiles with .prj in the NZMG/NZGD 49 projection and when I import into V11 its 50-100m out consistently. I can import exactly the same shp file into V9/10 and it places it in the right spot but its consistently out in V11.

I work in this projection all the time so its pretty frustrating. Also for some reason it will display NZMG (WGS84) in the bottom right hand corner of the screen when the project configuration is in NZMG (NZGD49). If I change the projection and then change it back it will fix it.

I exported the NZMG projection from V9 and V11 to compare and there are slight differences. Any way I can resolve this or else I am going to have to fall back to earlier version?

Thanks

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Can you provide the PRJ file that isn't loading properly in v11 so that I can take a look? Also, which v11 version are you using? If you aren't on v11.02 I would suggest downloading and installing that from the Download Trial link at http://www.globalmapper.com.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • TrustPowerTrustPower Global Mapper User Posts: 4
    edited April 2010
    Thanks - yes I have installed 11.02. Another interesting change is that with geo referenced jpg files (with jgw) it asks for the projection/datum whereas in earlier versions it determined this automatically?

    I assume I send you the files at support@globalmapper.com
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    A JGW file is just a world file for a JPG file that provides a mapping from the pixel coordinates of the JPG file to some coordinate system, but the JGW file doesn't indicate what that coordinate system is. In the absence of an additional file (like a PRJ file) providing the projection/coordinate system Global Mapper will ask the user. This behavior should be the same as always.

    You can either post the files here in a message or email them to support@globalmapper.com.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited April 2010
    In the absence of an additional file (like a PRJ file) providing the projection/coordinate system Global Mapper will ask the user. This behavior should be the same as always.

    Is there any way a user can circumvent the default behaviour, so that choosing New Zealand Map Grid from the list of projections will not initially select its datum partner, Geodetic Datum 1949, but WGS84?

    It doesn't ring any bells here. We just press 'N' twice, which brings up the NZMG/GD1949 pair, and hit enter. ('N' three times for the NZTM/NZGD2000 pair.)

    If there is a .prj file, and it's incorrect (as they often are), then it's a different story.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    By default when you switch projections the datum will stay the same, except in the case of those few projections (like NZMG) that only have a limited set of possible datums and the currently selected datum is not one of those. Since WGS84 is not one of the available datums for NZMG (although NZGD2000 is equivalent), if you have WGS84 selected and switch to NZMG you'll switch to the first datum in the list for NZMG.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited April 2010
    Good, thanks for explaining. So normally, to get NZMG paired with WGS84 (wrongly), you'd have to either (a) select NZMG, then manually switch from NZGD49 to WGS84, or (b) load data in the presence of an incorrect projection file, or (c) load a GeoTIFF that had been written with the wrong datum information, which (normally) would override other sources of information.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2010
    Currently you couldn't get NZMG paired with WGS84 in the projection selection dialog, but you could load a PRJ file or GeoTIFF with that mapping. It this is an issue I can add WGS84 as an allowed choice for NZMG very easily.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited April 2010
    No thanks Mike, it would be very strange to pair NZMG with WGS84. (I can't think of a reason to do it, not even a creative one.) So it's good that it can't be done manually in GM. I was only trying to wonder aloud how TrustPower's problem arose. We often see this sort of issue in client data—another example is always instructive. In this case I suppose it has to be that somewhere else in TrustPower's workflow, a .prj or a GeoTIFF has been made that mixes NZMG and WGS84.

    I'll stop speculating now and butt out. It will be interesting to see what the issue turns out to have been.
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