Introduce compatibility for cs2cs-style proj-strings into the 4D API.

Parameters such as towgs84, nadgrids and geoidgrids was previously only
handled by pj_transform(). This commit add a compatibility layer in
proj_create() by calling the pj_cs2cs_emulation_setup() function. This
function sets up a handful of predefined transformation objects on the
PJ object that is being created. Each of these transformation objects
are related to the cs2cs-style parameters we are trying to emulate in
the 4D API. That is, if the +towgs84 parameters is used we create
P->helmert with the parameters specified in +towgs84. Similarly for
+axis, +nadgrids and +geoidgrids. When these transformation objects
exists we use them in the prepare and finalize functions in pj_fwd/
pj_inv. If no cs2cs-style parametes are specified we skip those
parts of the prepare and finalizing steps.

Co-authored-by:Thomas Knudsen <thokn@sdfe.dk>
Co-authored-by:Kristian Evers <kristianevers@gmail.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/projects.h b/src/projects.h
index 86ca2524..aeaf09ae 100644
--- a/src/projects.h
+++ b/src/projects.h
@@ -349,6 +349,14 @@ struct PJconsts {
     enum pj_io_units left;          /* Flags for input/output coordinate types */
     enum pj_io_units right;
 
+    /* These PJs are used for implementing cs2cs style coordinate handling in the 4D API */
+    PJ *axisswap;
+    PJ *cart;
+    PJ *cart_wgs84;
+    PJ *helmert;
+    PJ *hgridshift;
+    PJ *vgridshift;
+
 
     /*************************************************************************************
 
@@ -394,7 +402,7 @@ struct PJconsts {
     double  from_greenwich;            /* prime meridian offset (in radians) */
     double  long_wrap_center;          /* 0.0 for -180 to 180, actually in radians*/
     int     is_long_wrap_set;
-    char    axis[4];                   /* TODO: Description needed */
+    char    axis[4];                   /* Axis order, pj_transform/pj_adjust_axis */
 
     /* New Datum Shift Grid Catalogs */
     char   *catalog_name;