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I would like to be able to add the NAD27 MEXICO projection to QGIS, MapInfo, etc. Global Mapper has this projection, and the prj file is: 

PROJCS["NAD_1927_UTM_Zone_13N",GEOGCS["GCS_North_American_1927",DATUM["D_NAD27_MEXICO",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-105],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]

Can anyone help me make this into an accurate, working prj4 file so I can add it as a custom projection in QGIS?

MrXsquared
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Jen
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    Hi Jen. When you import the shapefile in QGIS, what happens with the layer CRS? Check setting EPSG:26713 to it. You will need to know the datum transformation parameters. PROJ can tell you what think about the most appropiate if you can define a bounding box to search for NAD27 datum transformations. – Gabriel De Luca Jan 15 '20 at 22:47
  • Check this https://gis.stackexchange.com/questions/124322/reprojecting-between-nad27-and-wgs-84 – Gerardo Jimenez Jan 16 '20 at 13:28
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    The paramater for datum transformation is +towgs84=-12,130,190,0,0,0 in the question mentioned above the source documentation is mentioned – Gerardo Jimenez Jan 16 '20 at 13:33
  • Hola Gerardo. If I import the NAD27Mexico projected files into QGIS or MapInfo, they take on the NAD27 North America projection. Unfortunately, this is not exactly the same as the NAD27Mexico projection but both have the same EPSG number. It becomes very apparent when viewing drill hole collars on satellite imagery -- the drill hole points do not plot on the drill pads unless I open them in GlobalMapper in NAD27Mexico and reproject them into a more common projection. This is true of all the NAD27Mexico files, and I have many to convert to a more modern projection! – Jen Jan 16 '20 at 19:41

1 Answers1

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As seen in DATUM Enumeration - Blue Marble Geographics:

The following is a list of the datums built in to Global Mapper and the transformation parameters used to convert those datums. All parameters are given with respect to transforming from the given datum to WGS-84.

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Those parameters correspond with NAD27 to WGS 84 (18) datum transformation.

In QGIS, the layer must be in EPSG:26713 CRS, with the appropriate datum transformation:

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There are two ways to define a default datum transformation.

One is for the project, in Project ~> Properties menu, CRS tab:

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Or you can define a default datum transformation for all projects (except for those in which a different project default datum transformation overrides it), in Settings ~> Options menus, CRS tab:

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If you want to use a custom CRS instead, the following PROJ.4 string should work:

+proj=utm +zone=13 +ellps=clrk66 +towgs84=-12,130,190

If you are using QGIS 3.10, let me advise that some bugs in the datum trasnformations were discovered and you need to wait the QGIS 3.10.2 release, or install QGIS 3.10.1-23 (current master branch) or QGIS 3.11.0-58 (development branch) were seems to be fixed, or install QGIS 3.4.14 (current LTR) which seems not affected.

QGIS user manual, datum transformations:

Gabriel De Luca
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