[PROJ] Change of datum not working

[Mathieu Poulin]

When creating a transformation that requires a change of datum, it does not work. For instance, going from Geographic coordinates in WGS84 to UTM coordinates in NAD83CSRS. It does convert from geographic lat,lon to UTM projection easting,northing but the datum remains WGS84.

I am using Proj 8.2 (but I've also tried this with Proj 7.1 and 7.2) with C++. Here is the code with comments describing the values of the variables, the expected output of the code and the actual output of the code.

// ENTRY: x=-1614798.938 y=-3690228.026 z=4929942.509
GeographicLib::Geocentric::WGS84().Reverse(x, y, z, point.m_latitude, point.m_longitude, point.m_ellipsoidal_height);
// REVERSE: point.m_latitude=50.937434634728845 point.m_longitude=-113.63360224940385 point.m_m_ellipsoidal_height=1005.9387180001410
PJ_COORD coord = proj_coord(point.m_latitude, point.m_longitude, point.m_ellipsoidal_height, 0.0);
PJ* proj_from_WGS84_to_2956 = proj_create_crs_to_crs(0, "EPSG:4326", "EPSG:2956", 0);
PJ_XYZ proj_point_2 = proj_trans(proj_from_WGS84_to_2956, PJ_FWD, coord).xyz;
// EXPECTED RESULT: 314967.330, 5646169.740, 1006.379
// ACTUAL RESULT:   314967.085, 5646169.595, 1005.939

Am I doing something wrong? Am I missing something? If someone could help me out with this bit of code, it would be hugely appreciated.

Thanks,

 - Mathieu Poulin



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Mathieu Poulin

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