[PROJ] Geodetic to geographic conversions

[Even Rouault]

On jeudi 29 octobre 2020 08:25:24 CET Nicolas Bellaiche wrote:
> Hi all,
> 
> I need to migrate my old PROJ.4 C++ codes to PROJ-7.1.1 and I'm a bit stuck
> with the conversions geodetic <-> geographic coordinates (on the same
> datum).

By geodetic, you mean geocentric ?

> The only doc I could find is this single line but I haven't been
> able to deal with it:
> 
> 
> pj_latlong_from_proj
> 
> 
> No direct equivalent, but can be accomplished by chaining
> proj_create()<https://proj.org/development/reference/functions.html#c.proj_
> create>, proj_crs_get_horizontal_datum()
> andproj_create_geographic_crs_from_datum()

Something along:

PJ* datum = proj_crs_get_horizontal_datum(ctxt, geocentric_crs);
PJ* cs = proj_create_ellipsoidal_2D_cs(
  ctxt, PJ_ELLPS2D_LONGITUDE_LATITUDE, /* or PJ_ELLPS2D_LATITUDE_LONGITUDE */
  NULL, /* default unit name for Degree */
  0 /* default conversion factor from Degree to Radian */
);

/* or proj_create_ellipsoidal_3D_cs() depending on your needs */

PJ* geog_crs = proj_create_geographic_crs_from_datum(ctxt, NULL, datum, cs);
proj_destroy(cs);
proj_destroy(datum);

PJ* transf = proj_create_crs_to_crs(ctxt, geocentric_crs, geog_crs, NULL);

proj_trans(transf, ...);

proj_destroy(geog_crs);

Even

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