[Proj] WGS84 to NAD27 Coordinate conversion in Android

[Robb Main]

Thanks for the suggestion, Nicholas.

I do have the latest NTv2 gsb file (13.5MB!).

Unfortunately, I require an offline solution - internet &/or cell data
connections will often be unavailable.
For that matter, relying on the continued existence of 'governement funded'
tools might also be a concern.
Canada is not immune to arbitrary swings of the economic axe. Or they might
just move the tool to some other URL.
Either way would bork my app.
;-)



On Tue, Nov 13, 2018 at 4:02 PM Nicolas Cadieux <
nicolas.cadieux at archeotec.ca> wrote:

> 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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