PostGIS  2.3.7dev-r@@SVN_REVISION@@
double ptarray_length_spheroid ( const POINTARRAY pa,
const SPHEROID s 
)

Definition at line 2842 of file lwgeodetic.c.

References SPHEROID::a, SPHEROID::b, POINTARRAY::flags, FLAGS_GET_Z, geographic_point_init(), getPoint4d_p(), LW_FALSE, POINTARRAY::npoints, SPHEROID::radius, sphere_distance(), spheroid_distance(), POINT4D::x, POINT4D::y, and POINT4D::z.

Referenced by lwgeom_length_spheroid().

2843 {
2844  GEOGRAPHIC_POINT a, b;
2845  double za = 0.0, zb = 0.0;
2846  POINT4D p;
2847  int i;
2848  int hasz = LW_FALSE;
2849  double length = 0.0;
2850  double seglength = 0.0;
2851 
2852  /* Return zero on non-sensical inputs */
2853  if ( ! pa || pa->npoints < 2 )
2854  return 0.0;
2855 
2856  /* See if we have a third dimension */
2857  hasz = FLAGS_GET_Z(pa->flags);
2858 
2859  /* Initialize first point */
2860  getPoint4d_p(pa, 0, &p);
2861  geographic_point_init(p.x, p.y, &a);
2862  if ( hasz )
2863  za = p.z;
2864 
2865  /* Loop and sum the length for each segment */
2866  for ( i = 1; i < pa->npoints; i++ )
2867  {
2868  seglength = 0.0;
2869  getPoint4d_p(pa, i, &p);
2870  geographic_point_init(p.x, p.y, &b);
2871  if ( hasz )
2872  zb = p.z;
2873 
2874  /* Special sphere case */
2875  if ( s->a == s->b )
2876  seglength = s->radius * sphere_distance(&a, &b);
2877  /* Spheroid case */
2878  else
2879  seglength = spheroid_distance(&a, &b, s);
2880 
2881  /* Add in the vertical displacement if we're in 3D */
2882  if ( hasz )
2883  seglength = sqrt( (zb-za)*(zb-za) + seglength*seglength );
2884 
2885  /* Add this segment length to the total */
2886  length += seglength;
2887 
2888  /* B gets incremented in the next loop, so we save the value here */
2889  a = b;
2890  za = zb;
2891  }
2892  return length;
2893 }
double x
Definition: liblwgeom.h:351
double sphere_distance(const GEOGRAPHIC_POINT *s, const GEOGRAPHIC_POINT *e)
Given two points on a unit sphere, calculate their distance apart in radians.
Definition: lwgeodetic.c:913
int npoints
Definition: liblwgeom.h:370
double b
Definition: liblwgeom.h:313
double radius
Definition: liblwgeom.h:317
Point in spherical coordinates on the world.
Definition: lwgeodetic.h:47
#define LW_FALSE
Definition: liblwgeom.h:76
uint8_t flags
Definition: liblwgeom.h:368
#define FLAGS_GET_Z(flags)
Macros for manipulating the 'flags' byte.
Definition: liblwgeom.h:139
double z
Definition: liblwgeom.h:351
double a
Definition: liblwgeom.h:312
void geographic_point_init(double lon, double lat, GEOGRAPHIC_POINT *g)
Initialize a geographic point.
Definition: lwgeodetic.c:171
double spheroid_distance(const GEOGRAPHIC_POINT *a, const GEOGRAPHIC_POINT *b, const SPHEROID *spheroid)
Computes the shortest distance along the surface of the spheroid between two points.
Definition: lwspheroid.c:186
double y
Definition: liblwgeom.h:351
int getPoint4d_p(const POINTARRAY *pa, int n, POINT4D *point)
Definition: lwgeom_api.c:244

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