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i have a shapefile with .prj :

PROJCS["NAD_1927_UTM_Zone_17N",
GEOGCS["GCS_North_American_1927",
DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]],
PROJECTION["Transverse_Mercator"],
PARAMETER["False_Easting",1640416.666666667],
PARAMETER["False_Northing",0.0],
PARAMETER["Central_Meridian",-81.0],
PARAMETER["Scale_Factor",0.9996]
PARAMETER["Latitude_Of_Origin",0.0],
UNIT["Foot_US",0.3048006096012192]]

and my goal is to project this to google maps. I can transform in to web mercator using geotools, but there is a slight shift. I have a few questions:

  1. Is this some projection with a code registered under an authority?

    I dont think its NAD27 UTM 17N, cos params like easting differ

  2. Is there a .gsb to handle the shift, or how else can i handle it?

  3. Does use in this case user need to provide the Bursa wolf params himself?

Ideally, the system i build should be able to automatically handle such shapefiles, is it too much to aks?

  • 1
    if your search for PARAMETER["False_Easting",1640416.666666667] in downloads.esri.com/support/documentation/ims_/support_files/…, a lot of NAD_1983 CRSs pop up. There are EPSG Codes as well - maybe one of them is your CRS? It may help you find the -toWGS84 Parameters you need via spatialreference.org or epsg.io – copossum Nov 28 '19 at 8:14
  • It's EPSG::32067 but with a different name: NAD27 / BLM 17N (ftUS). Is the data in Canada or USA, because that will change which transformation and/or grid file(s) you need. – mkennedy Nov 30 '19 at 18:11
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  1. Probably, there are 206 possible projections based on that geogcrs, I can't find a way to limit epsg.io to a specific unit that might narrow it down.

  2. GeoTools will read that projection file and will automatically apply any grid shifts or bursa wolf parameters that are needed for the conversion to your target projection. To add a grid shift to the transform you may need to add the grid file (available on epsg.io and other places) if it is not already included in the GeoTools/GeoServer list.

  3. If they aren't in the projection then use the lenient flag in the call to CRS.findMathTransform(...). Or you can add them to the CRS if you know what they are.

  • 1. I found it ot be epsg.io/32067 2. i dont want to use lenient, so i get an exception then transforming. I try to set an AuthorityFactory and search for gsb files, that would do grid shift correction – george Nov 28 '19 at 9:01

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