Problem Displaying State Pland and State Plane HARN based

jeb2cavjeb2cav Global Mapper UserPosts: 3
edited April 2009 in Technical Support
Hi,

I'm working in the Virgina / Maryland area on a project and have downloaded imagery from the USGS Seamless Server site. The Maryland imagery is in State Plane 1900 feet. The Virginia Imagery is in State Plane 1902 feet, but is using NAD 83 HARN as the datum.

The Maryland data displays correctly for latitude, but is off by several degrees in longitude.

The Virginia data is off in both, by a large amount.

I've tried a number of manual manipulations to adjust/correct the display and nothing seems to work correctly. They do display "as expected" in other applications - but I'd prefer to use Global Mapper.

I'd appreciate some advice on what to do to properly display these rasters. I'm using 10.02. Thanks.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2009
    Are you being prompted to select a projection when you load the files? It sounds like the projection and/or datum is not being interpreted properly when the data is loaded. You can check the projection used for a file by opening the Control Center, then select the layer, then press Metadata and look at the Projection tab. You can correct the projection interpretation used by a layer by pressing the Options button on the Control Center and then correcting the projection on the Projection tab.

    You might also try getting the latest build of Global Mapper from http://www.globalmapper.com/global_mapper10.zip and extracting it over your existing installation to see if that makes any difference.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • jeb2cavjeb2cav Global Mapper User Posts: 3
    edited April 2009
    Hi Mike,

    Thanks for the quick reply. I had gone through all of that before, for what it's worth. One thing I noticed before in the metadata are the West, North, East and South lat/lon values - and as stated in the first email, both were incorrect for the VA data (NAD83 HARN), and the lat was incorrect for the MD state plan data (NAD 83).

    I downloaded the new exe and found that the MD state plane (and other NAD 83 I spot checked) now are generating as expected.

    However, the VA State plane case is unchanged.

    My assumption at this point is that the West, North, East, and South lat/lon values are generated by Global Mapper (as I don't see this information in the prj or tfw files associated with the imagery), and this is resulting in the display error.

    I will attach a text file showing the before and after of the MD NAD 83 case, as well as the metadata for the VA NAD83_HARN case.

    The coordinate system options for both have always appeared "correct" to me - NAD 83 feet or NAD 83 HARN feet. I've attached a jpg showing the outcome in the viewer, as well as the projection options displayed by Global Mapper for the VA case.

    I am not being prompted to enter a coordinate system on import.

    Joe
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2009
    It looks to me like the coordinates are actually in State Plane/VA South/meters, not feet. If I use meters as the units for the coordinates specified then the data comes in at the right place. Is there perhaps a TFW file with the TIFF file that might have different coordinates than what is in the TIFF file and could cause the problem. You can have the TFW coordinate preferred over those in the TIFF using an option on the General tab of the Configuration dialog, this may fix things.

    Otherwise, I have seen some files that use the incorrect EPSG projection code in the TIFF file for the state plane projection resulting in the wrong units being used. Typically this is using the meters code when feet are meant though and not the other way around.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • jeb2cavjeb2cav Global Mapper User Posts: 3
    edited April 2009
    Hi Mike,

    Thanks for this insight. These files from the USGS seamless come with a prj and tfw file. If I "hide" both the prj and the tfw, I am prompted for a coordinate system and selecting NAD 83 meters I get a good outcome in Global Mapper.

    Thanks for the insight and resulting work around.

    I am skeptical that these files are in fact in meters. All of this data states feet in the metadata files, and again, for what it's worth, displays as expected in other GIS tools (I prefer to use Global Mapper).

    I appreciate your timely response, ideas, and the new exe which cured the state plane, non-HARN condition I was experiencing.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2009
    I think what is most likely happening is that the TIFF file contains embedded coordinate information in State Plane/meters, but the TFW file has State Plane/feet coordinates and the PRJ file says State Plane/feet. By default, Global Mapper uses coordinates embedded in a GeoTIFF over those in a TFW world file, while some other applications use the TFW coordinates first. In this case where the embedded TIFF and TFW coordinates do not agree (although they should), you've got a 50% chance of getting the right one for the projection in the PRJ file. You can choose which set of coordinates is preferred in the Advanced Section of the General tab of the Configurtion dialog.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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