[PROJ] Vertical Transformations?

[Paul Ramsey]

Hey, all. Having gotten a working version of proj6 support running in
PostGIS, I'm trying to look for some of the goodies that users will
get when they upgrade. An obvious one is vertical transformations... I
tried this call:

postgis30=# select st_astext(st_transform('SRID=7406;POINT(-100 45
100)'::geometry, 5500));
                    st_astext
-------------------------------------------------
 POINT Z (-100.00039555444 44.9999807122224 100)
(1 row)

But as you can see, no vertical shift, even though 7406 is NGVD29 and
5500 is NAVD88. Is there another pairing I can use that should return
a vertical shift?

For reference the call is happening here:

https://github.com/pramsey/postgis/blob/svn-trunk-proj/liblwgeom/lwgeom_transform.c#L318

Maybe compound systems don't automatically do their thing when created
using proj_create_crs_to_crs() ?

Thanks!

P