Switch from gnomic to LAEA for the projection for the custom zones. Less perfect...

git-svn-id: http://svn.osgeo.org/postgis/trunk@10176 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/libpgcommon/lwgeom_transform.c b/libpgcommon/lwgeom_transform.c
index 238803644182c34c058abf278d523c709181e8b1..dd26c45282dbf3e9b88c5d9ed8ce0f45674e900c 100644 (file)
--- a/libpgcommon/lwgeom_transform.c
+++ b/libpgcommon/lwgeom_transform.c
@@ -407,14 +407,18 @@ static char* GetProj4String(int srid)
                {
                        snprintf(proj_str, maxproj4len, "+proj=utm +zone=%d +south +ellps=WGS84 +datum=WGS84 +units=m +no_defs", id - SRID_SOUTH_UTM_START + 1);
                }
-               /* Gnomic zones (about 30x30, larger in higher latitudes) */
-               else if ( id >= SRID_GNOMIC_START && id <= SRID_GNOMIC_END )
+               /* Lambert zones (about 30x30, larger in higher latitudes) */
+               /* There are three latitude zones, divided at -90,-60,-30,0,30,60,90. */
+               /* In yzones 2,3 (equator) zones, the longitudinal zones are divided every 30 degrees (12 of them) */
+               /* In yzones 1,4 (temperate) zones, the longitudinal zones are every 45 degrees (8 of them) */
+               /* In yzones 0,5 (polar) zones, the longitudinal zones are ever 90 degrees (4 of them) */
+               else if ( id >= SRID_LAEA_START && id <= SRID_LAEA_END )
                {
-                       int zone = id - SRID_GNOMIC_START;
+                       int zone = id - SRID_LAEA_START;
                        int xzone = zone % 20;
                        int yzone = zone / 20;
                        double lat_0 = 30.0 * (yzone - 3) + 15.0;
-                       double lon_0;
+                       double lon_0 = 0.0;
                        
                        /* The number of xzones is variable depending on yzone */
                        if  ( yzone == 2 || yzone == 3 )
@@ -426,7 +430,7 @@ static char* GetProj4String(int srid)
                        else
                                lwerror("Unknown yzone encountered!");
                        
-                       snprintf(proj_str, maxproj4len, "+proj=gnom +ellps=WGS84 +datum=WGS84 +lat_0=%g +lon_0=%g +units=m +no_defs", lat_0, lon_0);
+                       snprintf(proj_str, maxproj4len, "+proj=laea +ellps=WGS84 +datum=WGS84 +lat_0=%g +lon_0=%g +units=m +no_defs", lat_0, lon_0);
                }
                /* Lambert Azimuthal Equal Area South Pole */
                else if ( id == SRID_SOUTH_LAMBERT )

diff --git a/libpgcommon/lwgeom_transform.h b/libpgcommon/lwgeom_transform.h
index 11574df35fccfd0dcca3b66a90ce19ac5aa1de25..ee79179ccfb261661834588e54e1be6131dc9b28 100644 (file)
--- a/libpgcommon/lwgeom_transform.h
+++ b/libpgcommon/lwgeom_transform.h
@@ -52,7 +52,7 @@ void srid_is_latlong(FunctionCallInfo fcinfo, int srid);
 /**  End of UTM North zone, equivalent to EPSG:32660 */
 #define SRID_NORTH_UTM_END   999060
 
-/** Lambert Azimuthal Equal Area North Pole, equivalent to EPSG:3574 */
+/** Lambert Azimuthal Equal Area (LAEA) North Pole, equivalent to EPSG:3574 */
 #define SRID_NORTH_LAMBERT   999061
 
 /** PolarSteregraphic North, equivalent to EPSG:3995 */
@@ -64,17 +64,17 @@ void srid_is_latlong(FunctionCallInfo fcinfo, int srid);
 /**  Start of UTM South zone, equivalent to EPSG:32760 */
 #define SRID_SOUTH_UTM_END   999160
 
-/** Lambert Azimuthal Equal Area South Pole, equivalent to EPSG:3409 */
+/** Lambert Azimuthal Equal Area (LAEA) South Pole, equivalent to EPSG:3409 */
 #define SRID_SOUTH_LAMBERT   999161
 
 /** PolarSteregraphic South, equivalent to EPSG:3031 */
 #define SRID_SOUTH_STEREO    999162
 
-/** Gnomic zones start (6 latitude bands x up to 20 latitude bands) */
-#define SRID_GNOMIC_START 999163
+/** LAEA zones start (6 latitude bands x up to 20 longitude bands) */
+#define SRID_LAEA_START 999163
 
-/** Gnomic zones end (6 latitude bands x up to 20 latitude bands) */
-#define SRID_GNOMIC_END 999283
+/** LAEA zones end (6 latitude bands x up to 20 longitude bands) */
+#define SRID_LAEA_END 999283
 
 
 /** @} */

diff --git a/postgis/geography_measurement.c b/postgis/geography_measurement.c
index 57a6d8e3eb7e0edf2b6bd737538495fb9156b28c..76ac3bdd72560a51d0e0159a835511b220a835b5 100644 (file)
--- a/postgis/geography_measurement.c
+++ b/postgis/geography_measurement.c
@@ -774,9 +774,9 @@ Datum geography_bestsrid(PG_FUNCTION_ARGS)
        }
 
        /*
-       ** Can we fit into a custom Gnomic area? (30 degrees high, variable width) 
+       ** Can we fit into a custom LAEA area? (30 degrees high, variable width) 
        ** We will allow overlap into adjoining areas, but use a slightly narrower test (25) to try
-       ** and lower the worst case.
+       ** and minimize the worst case.
        ** Again, we are hoping the dateline doesn't trip us up much
        */
        if ( ywidth < 25.0 )
@@ -803,7 +803,7 @@ Datum geography_bestsrid(PG_FUNCTION_ARGS)
                /* Did we fit into an appropriate xzone? */
                if ( xzone != -1 )
                {
-                       PG_RETURN_INT32(SRID_GNOMIC_START + 20 * yzone + xzone);
+                       PG_RETURN_INT32(SRID_LAEA_START + 20 * yzone + xzone);
                }
        }