PostGIS  3.1.6dev-r@@SVN_REVISION@@

◆ geography_bestsrid()

Datum geography_bestsrid ( PG_FUNCTION_ARGS  )

Definition at line 798 of file geography_measurement.c.

799 {
800  GBOX gbox, gbox1, gbox2;
801  GSERIALIZED *g1 = NULL;
802  GSERIALIZED *g2 = NULL;
803  int empty1 = LW_FALSE;
804  int empty2 = LW_FALSE;
805  double xwidth, ywidth;
806  POINT2D center;
807  LWGEOM *lwgeom;
808 
809  /* Get our geometry objects loaded into memory. */
810  g1 = PG_GETARG_GSERIALIZED_P(0);
811  /* Synchronize our box types */
812  gbox1.flags = gserialized_get_lwflags(g1);
813  /* Calculate if the geometry is empty. */
814  empty1 = gserialized_is_empty(g1);
815 
816  /* Convert g1 to LWGEOM type */
817  lwgeom = lwgeom_from_gserialized(g1);
818 
819  /* Calculate a geocentric bounds for the objects */
820  if ( ! empty1 && gserialized_get_gbox_p(g1, &gbox1) == LW_FAILURE )
821  elog(ERROR, "Error in geography_bestsrid calling gserialized_get_gbox_p(g1, &gbox1)");
822 
823  POSTGIS_DEBUGF(4, "calculated gbox = %s", gbox_to_string(&gbox1));
824 
825  if ( !lwgeom_isfinite(lwgeom) ) {
826  elog(ERROR, "Error in geography_bestsrid calling with infinite coordinate geographies");
827  }
828  lwgeom_free(lwgeom);
829 
830  /* If we have a unique second argument, fill in all the necessary variables. */
831  if (PG_NARGS() > 1)
832  {
833  g2 = PG_GETARG_GSERIALIZED_P(1);
834  gbox2.flags = gserialized_get_lwflags(g2);
835  empty2 = gserialized_is_empty(g2);
836  if ( ! empty2 && gserialized_get_gbox_p(g2, &gbox2) == LW_FAILURE )
837  elog(ERROR, "Error in geography_bestsrid calling gserialized_get_gbox_p(g2, &gbox2)");
838 
839  /* Convert g2 to LWGEOM type */
840  lwgeom = lwgeom_from_gserialized(g2);
841 
842  if ( !lwgeom_isfinite(lwgeom) ) {
843  elog(ERROR, "Error in geography_bestsrid calling with second arg infinite coordinate geographies");
844  }
845  lwgeom_free(lwgeom);
846  }
847  /*
848  ** If no unique second argument, copying the box for the first
849  ** argument will give us the right answer for all subsequent tests.
850  */
851  else
852  {
853  gbox = gbox2 = gbox1;
854  }
855 
856  /* Both empty? We don't have an answer. */
857  if ( empty1 && empty2 )
858  PG_RETURN_NULL();
859 
860  /* One empty? We can use the other argument values as infill. Otherwise merge the boxen */
861  if ( empty1 )
862  gbox = gbox2;
863  else if ( empty2 )
864  gbox = gbox1;
865  else
866  gbox_union(&gbox1, &gbox2, &gbox);
867 
868  gbox_centroid(&gbox, &center);
869 
870  /* Width and height in degrees */
871  xwidth = 180.0 * gbox_angular_width(&gbox) / M_PI;
872  ywidth = 180.0 * gbox_angular_height(&gbox) / M_PI;
873 
874  POSTGIS_DEBUGF(2, "xwidth %g", xwidth);
875  POSTGIS_DEBUGF(2, "ywidth %g", ywidth);
876  POSTGIS_DEBUGF(2, "center POINT(%g %g)", center.x, center.y);
877 
878  /* Are these data arctic? Lambert Azimuthal Equal Area North. */
879  if ( center.y > 70.0 && ywidth < 45.0 )
880  {
881  PG_RETURN_INT32(SRID_NORTH_LAMBERT);
882  }
883 
884  /* Are these data antarctic? Lambert Azimuthal Equal Area South. */
885  if ( center.y < -70.0 && ywidth < 45.0 )
886  {
887  PG_RETURN_INT32(SRID_SOUTH_LAMBERT);
888  }
889 
890  /*
891  ** Can we fit these data into one UTM zone?
892  ** We will assume we can push things as
893  ** far as a half zone past a zone boundary.
894  ** Note we have no handling for the date line in here.
895  */
896  if ( xwidth < 6.0 )
897  {
898  int zone = floor((center.x + 180.0) / 6.0);
899 
900  if ( zone > 59 ) zone = 59;
901 
902  /* Are these data below the equator? UTM South. */
903  if ( center.y < 0.0 )
904  {
905  PG_RETURN_INT32( SRID_SOUTH_UTM_START + zone );
906  }
907  /* Are these data above the equator? UTM North. */
908  else
909  {
910  PG_RETURN_INT32( SRID_NORTH_UTM_START + zone );
911  }
912  }
913 
914  /*
915  ** Can we fit into a custom LAEA area? (30 degrees high, variable width)
916  ** We will allow overlap into adjoining areas, but use a slightly narrower test (25) to try
917  ** and minimize the worst case.
918  ** Again, we are hoping the dateline doesn't trip us up much
919  */
920  if ( ywidth < 25.0 )
921  {
922  int xzone = -1;
923  int yzone = 3 + floor(center.y / 30.0); /* (range of 0-5) */
924 
925  /* Equatorial band, 12 zones, 30 degrees wide */
926  if ( (yzone == 2 || yzone == 3) && xwidth < 30.0 )
927  {
928  xzone = 6 + floor(center.x / 30.0);
929  }
930  /* Temperate band, 8 zones, 45 degrees wide */
931  else if ( (yzone == 1 || yzone == 4) && xwidth < 45.0 )
932  {
933  xzone = 4 + floor(center.x / 45.0);
934  }
935  /* Arctic band, 4 zones, 90 degrees wide */
936  else if ( (yzone == 0 || yzone == 5) && xwidth < 90.0 )
937  {
938  xzone = 2 + floor(center.x / 90.0);
939  }
940 
941  /* Did we fit into an appropriate xzone? */
942  if ( xzone != -1 )
943  {
944  PG_RETURN_INT32(SRID_LAEA_START + 20 * yzone + xzone);
945  }
946  }
947 
948  /*
949  ** Running out of options... fall-back to Mercator
950  ** and hope for the best.
951  */
952  PG_RETURN_INT32(SRID_WORLD_MERCATOR);
953 
954 }
int gbox_union(const GBOX *g1, const GBOX *g2, GBOX *gout)
Update the output GBOX to be large enough to include both inputs.
Definition: gbox.c:135
char * gbox_to_string(const GBOX *gbox)
Allocate a string representation of the GBOX, based on dimensionality of flags.
Definition: gbox.c:392
int gserialized_get_gbox_p(const GSERIALIZED *g, GBOX *gbox)
Read the box from the GSERIALIZED or calculate it if necessary.
Definition: gserialized.c:65
LWGEOM * lwgeom_from_gserialized(const GSERIALIZED *g)
Allocate a new LWGEOM from a GSERIALIZED.
Definition: gserialized.c:239
int gserialized_is_empty(const GSERIALIZED *g)
Check if a GSERIALIZED is empty without deserializing first.
Definition: gserialized.c:152
lwflags_t gserialized_get_lwflags(const GSERIALIZED *g)
Read the flags from a GSERIALIZED and return a standard lwflag integer.
Definition: gserialized.c:18
#define LW_FALSE
Definition: liblwgeom.h:108
#define LW_FAILURE
Definition: liblwgeom.h:110
void lwgeom_free(LWGEOM *geom)
Definition: lwgeom.c:1138
int lwgeom_isfinite(const LWGEOM *lwgeom)
Check if a LWGEOM has any non-finite (NaN or Inf) coordinates.
Definition: lwgeom.c:2540
double gbox_angular_height(const GBOX *gbox)
GBOX utility functions to figure out coverage/location on the globe.
Definition: lwgeodetic.c:188
double gbox_angular_width(const GBOX *gbox)
Returns the angular width (longitudinal span) of the box in radians.
Definition: lwgeodetic.c:215
int gbox_centroid(const GBOX *gbox, POINT2D *out)
Computes the average(ish) center of the box and returns success.
Definition: lwgeodetic.c:267
lwflags_t flags
Definition: liblwgeom.h:367
double y
Definition: liblwgeom.h:404
double x
Definition: liblwgeom.h:404

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

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