[gdal-dev] Add Mercator_variant_A method?

[Brad Hards]

I'm looking at geopackage support, and particularly at the NGA's draft 
"profile". 

It defines (and references) some spatial reference systems, including some 
interesting variations that will require more work later. For tonight, lets 
look at just one case:
PROJCS["WGS 84 / World Mercator",
	GEOGCS["WGS 84",
		DATUM["World Geodetic System 1984",
			SPHEROID["WGS 84",6378137,298.257223563,
				AUTHORITY["EPSG","7030"]],
			AUTHORITY["EPSG","6326"]],
		PRIMEM["Greenwich",0,
			AUTHORITY["EPSG","8901"]],
		UNIT["degree",0.0174532925199433,
			AUTHORITY["EPSG","9122"]],
		AUTHORITY["EPSG","4326"]],
	PROJECTION["Mercator_variant_A",
		AUTHORITY["EPSG","9804"]],
	PARAMETER["Latitude of natural origin",0],
	PARAMETER["Longitude of natural origin",0],
	PARAMETER["Scale factor at natural origin",1],
	PARAMETER["False easting",0],
	PARAMETER["False northing",0],		
	UNIT["metre",1,
		AUTHORITY["EPSG","9001"]],
	AXIS["Easting",EAST],
	AXIS["Northing",NORTH],	
	AUTHORITY["EPSG","3395"]]

The problematic part is that "PROJECTION" definition. I was originally going to 
argue it should be Mercator_1SP, but it looks like the EPSG decided to change 
it (in EPSG::2010.058) to this new "Mercator_variant_A" form, and keep the 
"Mercator_1SP" form as an alias.

Should we add the new form, with a change like:

diff --git a/gdal/ogr/ogr_srs_api.h b/gdal/ogr/ogr_srs_api.h
index 04dcf04..4349c06 100644
--- a/gdal/ogr/ogr_srs_api.h
+++ b/gdal/ogr/ogr_srs_api.h
@@ -136,6 +136,8 @@ typedef enum {
                                 "Lambert_Azimuthal_Equal_Area"
 #define SRS_PT_MERCATOR_1SP     "Mercator_1SP"
 #define SRS_PT_MERCATOR_2SP     "Mercator_2SP"
+#define SRS_PT_MERCATOR_VARIANT_A                                       \
+                                "Mercator_variant_A"
 // Mercator_Auxiliary_Sphere is used used by ESRI to mean EPSG:3875
 #define SRS_PT_MERCATOR_AUXILIARY_SPHERE                                 \
                                 "Mercator_Auxiliary_Sphere"
diff --git a/gdal/ogr/ogr_srs_proj4.cpp b/gdal/ogr/ogr_srs_proj4.cpp
index 002ef07..32772ba 100644
--- a/gdal/ogr/ogr_srs_proj4.cpp
+++ b/gdal/ogr/ogr_srs_proj4.cpp
@@ -1650,7 +1650,7 @@ OGRErr OGRSpatialReference::exportToProj4( char ** 
ppszProj4 ) const
                  GetNormProjParm(SRS_PP_FALSE_NORTHING,0.0) );
     }
 
-    else if( EQUAL(pszProjection,SRS_PT_MERCATOR_1SP) )
+    else if( EQUAL(pszProjection,SRS_PT_MERCATOR_1SP) || 
EQUAL(pszProjection,SRS_PT_MERCATOR_VARIANT_A) )
     {
         if( GetNormProjParm(SRS_PP_LATITUDE_OF_ORIGIN,0.0) == 0.0 )
             CPLsprintf( szProj4+strlen(szProj4),