PostGIS  2.5.0dev-r@@SVN_REVISION@@
Datum geography_bestsrid ( PG_FUNCTION_ARGS  )

Definition at line 778 of file geography_measurement.c.

References GBOX::flags, GSERIALIZED::flags, gbox_angular_height(), gbox_angular_width(), gbox_centroid(), gbox_to_string(), gbox_union(), gserialized_get_gbox_p(), gserialized_is_empty(), LW_FAILURE, LW_FALSE, POINT2D::x, and POINT2D::y.

779 {
780  GBOX gbox, gbox1, gbox2;
781  GSERIALIZED *g1 = NULL;
782  GSERIALIZED *g2 = NULL;
783  int empty1 = LW_FALSE;
784  int empty2 = LW_FALSE;
785  double xwidth, ywidth;
786  POINT2D center;
787 
788  Datum d1 = PG_GETARG_DATUM(0);
789  Datum d2 = PG_GETARG_DATUM(1);
790 
791  /* Get our geometry objects loaded into memory. */
792  g1 = (GSERIALIZED*)PG_DETOAST_DATUM(d1);
793  /* Synchronize our box types */
794  gbox1.flags = g1->flags;
795  /* Calculate if the geometry is empty. */
796  empty1 = gserialized_is_empty(g1);
797  /* Calculate a geocentric bounds for the objects */
798  if ( ! empty1 && gserialized_get_gbox_p(g1, &gbox1) == LW_FAILURE )
799  elog(ERROR, "Error in geography_bestsrid calling gserialized_get_gbox_p(g1, &gbox1)");
800 
801  POSTGIS_DEBUGF(4, "calculated gbox = %s", gbox_to_string(&gbox1));
802 
803  /* If we have a unique second argument, fill in all the necessary variables. */
804  if ( d1 != d2 )
805  {
806  g2 = (GSERIALIZED*)PG_DETOAST_DATUM(d2);
807  gbox2.flags = g2->flags;
808  empty2 = gserialized_is_empty(g2);
809  if ( ! empty2 && gserialized_get_gbox_p(g2, &gbox2) == LW_FAILURE )
810  elog(ERROR, "Error in geography_bestsrid calling gserialized_get_gbox_p(g2, &gbox2)");
811  }
812  /*
813  ** If no unique second argument, copying the box for the first
814  ** argument will give us the right answer for all subsequent tests.
815  */
816  else
817  {
818  gbox = gbox2 = gbox1;
819  }
820 
821  /* Both empty? We don't have an answer. */
822  if ( empty1 && empty2 )
823  PG_RETURN_NULL();
824 
825  /* One empty? We can use the other argument values as infill. Otherwise merge the boxen */
826  if ( empty1 )
827  gbox = gbox2;
828  else if ( empty2 )
829  gbox = gbox1;
830  else
831  gbox_union(&gbox1, &gbox2, &gbox);
832 
833  gbox_centroid(&gbox, &center);
834 
835  /* Width and height in degrees */
836  xwidth = 180.0 * gbox_angular_width(&gbox) / M_PI;
837  ywidth = 180.0 * gbox_angular_height(&gbox) / M_PI;
838 
839  POSTGIS_DEBUGF(2, "xwidth %g", xwidth);
840  POSTGIS_DEBUGF(2, "ywidth %g", ywidth);
841  POSTGIS_DEBUGF(2, "center POINT(%g %g)", center.x, center.y);
842 
843  /* Are these data arctic? Lambert Azimuthal Equal Area North. */
844  if ( center.y > 70.0 && ywidth < 45.0 )
845  {
846  PG_RETURN_INT32(SRID_NORTH_LAMBERT);
847  }
848 
849  /* Are these data antarctic? Lambert Azimuthal Equal Area South. */
850  if ( center.y < -70.0 && ywidth < 45.0 )
851  {
852  PG_RETURN_INT32(SRID_SOUTH_LAMBERT);
853  }
854 
855  /*
856  ** Can we fit these data into one UTM zone?
857  ** We will assume we can push things as
858  ** far as a half zone past a zone boundary.
859  ** Note we have no handling for the date line in here.
860  */
861  if ( xwidth < 6.0 )
862  {
863  int zone = floor((center.x + 180.0) / 6.0);
864 
865  if ( zone > 59 ) zone = 59;
866 
867  /* Are these data below the equator? UTM South. */
868  if ( center.y < 0.0 )
869  {
870  PG_RETURN_INT32( SRID_SOUTH_UTM_START + zone );
871  }
872  /* Are these data above the equator? UTM North. */
873  else
874  {
875  PG_RETURN_INT32( SRID_NORTH_UTM_START + zone );
876  }
877  }
878 
879  /*
880  ** Can we fit into a custom LAEA area? (30 degrees high, variable width)
881  ** We will allow overlap into adjoining areas, but use a slightly narrower test (25) to try
882  ** and minimize the worst case.
883  ** Again, we are hoping the dateline doesn't trip us up much
884  */
885  if ( ywidth < 25.0 )
886  {
887  int xzone = -1;
888  int yzone = 3 + floor(center.y / 30.0); /* (range of 0-5) */
889 
890  /* Equatorial band, 12 zones, 30 degrees wide */
891  if ( (yzone == 2 || yzone == 3) && xwidth < 30.0 )
892  {
893  xzone = 6 + floor(center.x / 30.0);
894  }
895  /* Temperate band, 8 zones, 45 degrees wide */
896  else if ( (yzone == 1 || yzone == 4) && xwidth < 45.0 )
897  {
898  xzone = 4 + floor(center.x / 45.0);
899  }
900  /* Arctic band, 4 zones, 90 degrees wide */
901  else if ( (yzone == 0 || yzone == 5) && xwidth < 90.0 )
902  {
903  xzone = 2 + floor(center.x / 90.0);
904  }
905 
906  /* Did we fit into an appropriate xzone? */
907  if ( xzone != -1 )
908  {
909  PG_RETURN_INT32(SRID_LAEA_START + 20 * yzone + xzone);
910  }
911  }
912 
913  /*
914  ** Running out of options... fall-back to Mercator
915  ** and hope for the best.
916  */
917  PG_RETURN_INT32(SRID_WORLD_MERCATOR);
918 
919 }
int gserialized_get_gbox_p(const GSERIALIZED *g, GBOX *box)
Read the bounding box off a serialization and calculate one if it is not already there.
Definition: g_serialized.c:639
char * gbox_to_string(const GBOX *gbox)
Allocate a string representation of the GBOX, based on dimensionality of flags.
Definition: g_box.c:399
int gbox_centroid(const GBOX *gbox, POINT2D *out)
Computes the average(ish) center of the box and returns success.
Definition: lwgeodetic.c:258
int gserialized_is_empty(const GSERIALIZED *g)
Check if a GSERIALIZED is empty without deserializing first.
Definition: g_serialized.c:178
#define LW_FAILURE
Definition: liblwgeom.h:78
double x
Definition: liblwgeom.h:327
#define LW_FALSE
Definition: liblwgeom.h:76
double y
Definition: liblwgeom.h:327
int gbox_union(const GBOX *g1, const GBOX *g2, GBOX *gout)
Update the output GBOX to be large enough to include both inputs.
Definition: g_box.c:142
uint8_t flags
Definition: liblwgeom.h:290
double gbox_angular_height(const GBOX *gbox)
GBOX utility functions to figure out coverage/location on the globe.
Definition: lwgeodetic.c:179
uint8_t flags
Definition: liblwgeom.h:382
double gbox_angular_width(const GBOX *gbox)
Returns the angular width (longitudinal span) of the box in radians.
Definition: lwgeodetic.c:206

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