[PROJ] Problems with CGVD28 height

[Javier Jimenez Shaw]

Hi

I'm trying to convert from WGS84 (or NAD83, I do not mind)  to "MTM zone 1
+ CGVD28 height" in Canada.
I know that the area of use of "MTM zone 1" and "CGVD28 height" do not
intersect. But they told me "Canadian agencies still require this
datum [CGVD28]
throughout all of Canada." Actually the geoid model grid file
[ca_nrc_HT2_1997.tif:
Canada, Natural Resources Canada, NAD83(CSRS)v2 (EPSG:8235) to CGVD28
height (EPSG:5713)] covers much more than the CRS area of use.

projinfo says something that makes sense to me:

PROJ_NETWORK=ON projinfo -s EPSG:4979 -t EPSG:32181+5713 -o proj
--spatial-test intersects

Candidate operations found: 303
-------------------------------------
Operation No. 1:

unknown id, Inverse of NAD83 to WGS 84 (6) + NAD83 to NAD83(CSRS)v2 (1) +
NAD83(CSRS)v2 to CGVD28 height (1) + Inverse of NAD83 to NAD83(CSRS)v2 (1)
+ MTM zone 1, 4.55 m, unknown domain of validity

PROJ string:
+proj=pipeline
  +step +proj=axisswap +order=2,1
  +step +proj=unitconvert +xy_in=deg +xy_out=rad
  +step +inv +proj=vgridshift +grids=ca_nrc_HT2_1997.tif +multiplier=1
  +step +inv +proj=hgridshift +grids=ca_nrc_NA83SCRS.tif
  +step +proj=tmerc +lat_0=0 +lon_0=-53 +k=0.9999 +x_0=304800 +y_0=0
+ellps=GRS80

But cs2cs is not doing any vertical transformation:

echo 47.741422 -53.613219 0 | PROJ_NETWORK=ON cs2cs EPSG:4979
EPSG:32181+5713 --3d
258814.79 5289330.04 0.00

Running with PROJ_DEBUG=3 it ends with
Using coordinate operation Inverse of Transformation from CGVD28 height to
WGS 84 (ballpark vertical transformation, without ellipsoid height to
vertical height correction) + Inverse of Ballpark geographic offset from
NAD83 to WGS 84 + MTM zone 1
that makes sense with the no-change in elevation.


Why is that happening?

I do not care so much about the version of NAD83. I tried with some and I
get the same result.
The same with the source CRS. I use WGS84, but can be any flavour of NAD83.

Thanks.
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