[PROJ] Needs a sanity check on Vertical Transformation

[Even Rouault]

On vendredi 1 novembre 2019 13:12:11 CET YK_climate wrote:
> Hello,
> I have been trying to perform vertical transformation with Proj for a few
> days now, I think I am done but I am in some help to be sure I didn't make
> some stupid mistakes!
> I am looking at getting coordinates in WGS84-Ellipsoid to WG84-EGM96,WG84-
> EGM2008 and to NAD83(2011)GEOID12B.
> 
> Here is what I have working so far :
> WGS84-EGM2008 : cs2cs EPSG:4979 EPSG:4326+3855
> WGS84-EGM96    : cs2cs EPSG:4979 EPSG:4326+5773
> Is this correct?

Yes

> 
> So naturally I thought that GEOID12B would be as easy :
> NAD83(2011)-GEOID12B    : cs2cs EPSG:4979 EPSG:6319+5703 <= no vertical
> change
> NAD83(2011)-GEOID12B    : cs2cs EPSG:4979 EPSG:5498         <= no vertical
> change

As the target SRS here use the NAVD88 height vertical CRS, but in EPSG, there 
is no transformation from NAVD88 to WGS84, then PROJ < 6.2.1 didn't do any 
vertical change.

Starting with PROJ 6.2.1, it will use the NAVD88->NAD83/NAD83(2011) grids, so 
GEOID12B if that's what you've available, as a fallback.

$ ~/proj/install-proj-6.2.1/bin/projinfo -s EPSG:4979 -t EPSG:5498  --spatial-
test intersects

Candidate operations found: 294
-------------------------------------
Operation n°1:

unknown id, NAD83(2011) to NAVD88 height (1) + Inverse of NAD83 to WGS 84 (1), 
4.02 m, USA - CONUS - onshore, at least one grid missing

PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert 
+xy_in=deg +xy_out=rad +step +inv +proj=vgridshift +grids=g2012bu0.gtx 
+multiplier=1 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step 
+proj=axisswap +order=2,1



Even

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