[Proj] WGS84 to NAD27 Coordinate conversion in Android

[Nicolas Cadieux]

Hi,
Comments below..

> Le 13 nov. 2018 à 15:03, Robb Main <rmain.mws at gmail.com> a écrit :
> 
> I need to convert WGS84 (lat, long) coordinates from GPS to NAD27 UTM Eastings & Northings coordinates, primarily in Canada, in an Android environment. To maximize accuracy of the end result, I believe the NTv2 grid corrections must be applied (though adding 13.5MB to the final solution is not desireable).

Yes this is correct.  The first step will be to go from WGS84 transit to NAD83(CSRS) and then to NAD27 using the grid files.  Make sure you have the last version of the grid from 
https://open.canada.ca/en/suggested-datasets/ntv2-grid-shift-files-gsb.

Perhaps the easiest way is to link the android tool to the nrcan web tools?  It depends on the availability of wifi or cell coverage.

http://webappd.geod.nrcan.gc.ca/geod/tools-outils/trx.php?locale=fr&wbdisable=true

http://webapp.geod.nrcan.gc.ca/geod/tools-outils/ntv2.php

Good luck

> 
> I've looked at Proj.4 codebase, and I'm not at all sure it's the best tool for this purpose. The JNI support for proj.4 appears to be for java support under linux/windows/macos. GDAL uses proj.4 & appears to build for android ( https://trac.osgeo.org/gdal/wiki/BuildingForAndroid ), so it _IS_ possible (with some pain), though I'm not sure this is current info. Regardless, GDAL is overkill for my needs, as all I need is coordinates. 
> 
> I also found the proj4j library (a java port of the proj4 code - http://svn.osgeo.org/metacrs/proj4j/trunk/src/README.html), though it looks like it was last updated 5 years ago, and its not clear if grid support was ever fully implemented / operational.
> 
> I found CTS ( https://github.com/orbisgis/cts ), which is a straight JAVA library, implementing the required tranformations & supporting grids, but there is little information / no examples on its use. Since it is pure java, I expect it would be easier to implement in an android build environment.
> 
> Please comment on the above if you have experience with them, or point me in the right direction if you have some other suggestion.
> 
> Thank you.
> 
> 
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