Oblique Mercator projections not preserved in GTiff

[Mike Taves]

Oblique Mercator projections ​EPSG:29700 and ​EPSG:9702 are not preserved in GTiff files.

There are seemingly random differences with various parameters in PROJ.4 and WKT outputs. See #5897 for test_prj_roundtrip, and run:

for code in [29700, 29702]:
    print(test_prj_roundtrip(code, True, True))

with output

EPSG:29700 
Differences in PROJ.4:
- +proj=omerc +lat_0=-18.9 +lonc=44.10000000000001 +alpha=18.9 +k=0.9995000000000001 +x_0=400000 +y_0=800000 +gamma=18.9 +ellps=intl +towgs84=-189,-242,-91,0,0,0,0 +pm=paris +units=m +no_defs 
?                      ^ ^       ^^ ^^                     ^ ^                                                       ^ ^                                                ^^^^^
+ +proj=omerc +lat_0=-17.01 +lonc=39.69000000000001 +alpha=17.01 +k=0.9995000000000001 +x_0=400000 +y_0=800000 +gamma=17.01 +ellps=intl +towgs84=-189,-242,-91,0,0,0,0 +pm=2.5969213 +units=m +no_defs 
?                      ^ ^^       ^^ ^^                     ^ ^^                                                       ^ ^^                                                ^^^^^^^^^
Differences in WKT:
- PROJCS["Tananarive (Paris) / Laborde Grid (deprecated)",
?                                          -------------
+ PROJCS["Tananarive (Paris) / Laborde Grid",
      GEOGCS["Tananarive (Paris)",
          DATUM["Tananarive_1925_Paris",
-             SPHEROID["International 1924",6378388,297,
+             SPHEROID["International 1924",6378388,297.0000000000014,
?                                                      ++++++++++++++
                  AUTHORITY["EPSG","7022"]],
              TOWGS84[-189,-242,-91,0,0,0,0],
              AUTHORITY["EPSG","6810"]],
-         PRIMEM["Paris",2.33722917,
?                           ^^^^^^^
+         PRIMEM["Paris",2.5969213],
?                          ++++++ ^
-             AUTHORITY["EPSG","8903"]],
-         UNIT["grad",0.01570796326794897,
+         UNIT["grad",0.01570796326794897],
?                                        +
-             AUTHORITY["EPSG","9105"]],
          AUTHORITY["EPSG","4810"]],
      PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],
-     PARAMETER["latitude_of_center",-21],
?                                     -
+     PARAMETER["latitude_of_center",-18.9],
?                                      +++
-     PARAMETER["longitude_of_center",49],
?                                      ^
+     PARAMETER["longitude_of_center",44.1],
?                                      ^^^
-     PARAMETER["azimuth",21],
?                         -
+     PARAMETER["azimuth",18.9],
?                          +++
-     PARAMETER["rectified_grid_angle",21],
?                                      -
+     PARAMETER["rectified_grid_angle",18.9],
?                                       +++
      PARAMETER["scale_factor",0.9995],
      PARAMETER["false_easting",400000],
      PARAMETER["false_northing",800000],
      UNIT["metre",1,
          AUTHORITY["EPSG","9001"]],
-     AXIS["X",EAST],
-     AXIS["Y",NORTH],
      AUTHORITY["EPSG","29700"]]
EPSG:29702 
Differences in PROJ.4:
- +proj=omerc +lat_0=-18.9 +lonc=44.10000000000001 +alpha=18.9 +k=0.9995000000000001 +x_0=400000 +y_0=800000 +gamma=18.9 +ellps=intl +towgs84=-189,-242,-91,0,0,0,0 +pm=paris +units=m +no_defs 
?                      ^ ^       ^^ ^^                     ^ ^                                                       ^ ^                                                ^^^^^
+ +proj=omerc +lat_0=-17.01 +lonc=39.69000000000001 +alpha=17.01 +k=0.9995000000000001 +x_0=400000 +y_0=800000 +gamma=17.01 +ellps=intl +towgs84=-189,-242,-91,0,0,0,0 +pm=2.5969213 +units=m +no_defs 
?                      ^ ^^       ^^ ^^                     ^ ^^                                                       ^ ^^                                                ^^^^^^^^^
Differences in WKT:
  PROJCS["Tananarive (Paris) / Laborde Grid approximation",
      GEOGCS["Tananarive (Paris)",
          DATUM["Tananarive_1925_Paris",
-             SPHEROID["International 1924",6378388,297,
+             SPHEROID["International 1924",6378388,297.0000000000014,
?                                                      ++++++++++++++
                  AUTHORITY["EPSG","7022"]],
              TOWGS84[-189,-242,-91,0,0,0,0],
              AUTHORITY["EPSG","6810"]],
-         PRIMEM["Paris",2.33722917,
?                           ^^^^^^^
+         PRIMEM["Paris",2.5969213],
?                          ++++++ ^
-             AUTHORITY["EPSG","8903"]],
-         UNIT["grad",0.01570796326794897,
+         UNIT["grad",0.01570796326794897],
?                                        +
-             AUTHORITY["EPSG","9105"]],
          AUTHORITY["EPSG","4810"]],
      PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],
-     PARAMETER["latitude_of_center",-21],
?                                     -
+     PARAMETER["latitude_of_center",-18.9],
?                                      +++
-     PARAMETER["longitude_of_center",49],
?                                      ^
+     PARAMETER["longitude_of_center",44.1],
?                                      ^^^
-     PARAMETER["azimuth",21],
?                         -
+     PARAMETER["azimuth",18.9],
?                          +++
-     PARAMETER["rectified_grid_angle",21],
?                                      -
+     PARAMETER["rectified_grid_angle",18.9],
?                                       +++
      PARAMETER["scale_factor",0.9995],
      PARAMETER["false_easting",400000],
      PARAMETER["false_northing",800000],
      UNIT["metre",1,
          AUTHORITY["EPSG","9001"]],
      AUTHORITY["EPSG","29702"]]

[Even Rouault]

Same as #5899 : issue with GRAD