<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Hi,</div><div>Comments below..</div><div><br>Le 13 nov. 2018 à 15:03, Robb Main <<a href="mailto:rmain.mws@gmail.com">rmain.mws@gmail.com</a>> a écrit :<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">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).</div></div></div></div></div></blockquote><div><br></div>Yes this is correct. The first step will be to go from WGS84 transit to <span style="background-color: rgba(255, 255, 255, 0);">NAD83(CSRS) and then to NAD27 using the grid files. </span>Make sure you have the last version of the grid from <div><div><a href="https://open.canada.ca/en/suggested-datasets/ntv2-grid-shift-files-gsb">https://open.canada.ca/en/suggested-datasets/ntv2-grid-shift-files-gsb</a>.</div><div><br></div><div>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.</div><div><br></div><div><a href="http://webappd.geod.nrcan.gc.ca/geod/tools-outils/trx.php?locale=fr&wbdisable=true">http://webappd.geod.nrcan.gc.ca/geod/tools-outils/trx.php?locale=fr&wbdisable=true</a></div><div><div><div><br></div><div><a href="http://webapp.geod.nrcan.gc.ca/geod/tools-outils/ntv2.php">http://webapp.geod.nrcan.gc.ca/geod/tools-outils/ntv2.php</a></div><div><br></div><div>Good luck</div><div><br><blockquote type="cite"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><br></div><div>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 ( <a href="https://trac.osgeo.org/gdal/wiki/BuildingForAndroid">https://trac.osgeo.org/gdal/wiki/BuildingForAndroid</a> ), 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. </div><div><br></div><div>I also found the proj4j library (a java port of the proj4 code - <a href="http://svn.osgeo.org/metacrs/proj4j/trunk/src/README.html">http://svn.osgeo.org/metacrs/proj4j/trunk/src/README.html</a>), though it looks like it was last updated 5 years ago, and its not clear if grid support was ever fully implemented / operational.</div><div><br></div><div>I found CTS ( <a href="https://github.com/orbisgis/cts">https://github.com/orbisgis/cts</a> ), 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.</div><div><br></div><div>Please comment on the above if you have experience with them, or point me in the right direction if you have some other suggestion.</div><div><br></div><div>Thank you.</div><div><br></div><div><br></div></div></div></div></div>
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