PostGIS  2.2.7dev-r@@SVN_REVISION@@
int lw_dist2d_seg_seg ( const POINT2D A,
const POINT2D B,
const POINT2D C,
const POINT2D D,
DISTPTS dl 
)

Finds the shortest distance between two segments.

This function is changed so it is not doing any comparasion of distance but just sending every possible combination further to lw_dist2d_pt_seg

Definition at line 1802 of file measures.c.

References DIST_MAX, DIST_MIN, DISTPTS::distance, lw_dist2d_pt_seg(), LW_FALSE, LW_TRUE, LWDEBUGF, lwerror(), DISTPTS::mode, DISTPTS::p1, DISTPTS::p2, r, s, DISTPTS::twisted, POINT2D::x, and POINT2D::y.

Referenced by lw_dist2d_arc_arc(), lw_dist2d_ptarray_ptarray(), and lw_dist2d_seg_arc().

1803 {
1804  double s_top, s_bot,s;
1805  double r_top, r_bot,r;
1806 
1807  LWDEBUGF(2, "lw_dist2d_seg_seg [%g,%g]->[%g,%g] by [%g,%g]->[%g,%g]",
1808  A->x,A->y,B->x,B->y, C->x,C->y, D->x, D->y);
1809 
1810  /*A and B are the same point */
1811  if ( ( A->x == B->x) && (A->y == B->y) )
1812  {
1813  return lw_dist2d_pt_seg(A,C,D,dl);
1814  }
1815  /*U and V are the same point */
1816 
1817  if ( ( C->x == D->x) && (C->y == D->y) )
1818  {
1819  dl->twisted= ((dl->twisted) * (-1));
1820  return lw_dist2d_pt_seg(D,A,B,dl);
1821  }
1822  /* AB and CD are line segments */
1823  /* from comp.graphics.algo
1824 
1825  Solving the above for r and s yields
1826  (Ay-Cy)(Dx-Cx)-(Ax-Cx)(Dy-Cy)
1827  r = ----------------------------- (eqn 1)
1828  (Bx-Ax)(Dy-Cy)-(By-Ay)(Dx-Cx)
1829 
1830  (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
1831  s = ----------------------------- (eqn 2)
1832  (Bx-Ax)(Dy-Cy)-(By-Ay)(Dx-Cx)
1833  Let P be the position vector of the intersection point, then
1834  P=A+r(B-A) or
1835  Px=Ax+r(Bx-Ax)
1836  Py=Ay+r(By-Ay)
1837  By examining the values of r & s, you can also determine some other limiting conditions:
1838  If 0<=r<=1 & 0<=s<=1, intersection exists
1839  r<0 or r>1 or s<0 or s>1 line segments do not intersect
1840  If the denominator in eqn 1 is zero, AB & CD are parallel
1841  If the numerator in eqn 1 is also zero, AB & CD are collinear.
1842 
1843  */
1844  r_top = (A->y-C->y)*(D->x-C->x) - (A->x-C->x)*(D->y-C->y);
1845  r_bot = (B->x-A->x)*(D->y-C->y) - (B->y-A->y)*(D->x-C->x);
1846 
1847  s_top = (A->y-C->y)*(B->x-A->x) - (A->x-C->x)*(B->y-A->y);
1848  s_bot = (B->x-A->x)*(D->y-C->y) - (B->y-A->y)*(D->x-C->x);
1849 
1850  if ( (r_bot==0) || (s_bot == 0) )
1851  {
1852  if ((lw_dist2d_pt_seg(A,C,D,dl)) && (lw_dist2d_pt_seg(B,C,D,dl)))
1853  {
1854  dl->twisted= ((dl->twisted) * (-1)); /*here we change the order of inputted geometrys and that we notice by changing sign on dl->twisted*/
1855  return ((lw_dist2d_pt_seg(C,A,B,dl)) && (lw_dist2d_pt_seg(D,A,B,dl))); /*if all is successful we return true*/
1856  }
1857  else
1858  {
1859  return LW_FALSE; /* if any of the calls to lw_dist2d_pt_seg goes wrong we return false*/
1860  }
1861  }
1862 
1863  s = s_top/s_bot;
1864  r= r_top/r_bot;
1865 
1866  if (((r<0) || (r>1) || (s<0) || (s>1)) || (dl->mode == DIST_MAX))
1867  {
1868  if ((lw_dist2d_pt_seg(A,C,D,dl)) && (lw_dist2d_pt_seg(B,C,D,dl)))
1869  {
1870  dl->twisted= ((dl->twisted) * (-1)); /*here we change the order of inputted geometrys and that we notice by changing sign on dl->twisted*/
1871  return ((lw_dist2d_pt_seg(C,A,B,dl)) && (lw_dist2d_pt_seg(D,A,B,dl))); /*if all is successful we return true*/
1872  }
1873  else
1874  {
1875  return LW_FALSE; /* if any of the calls to lw_dist2d_pt_seg goes wrong we return false*/
1876  }
1877  }
1878  else
1879  {
1880  if (dl->mode == DIST_MIN) /*If there is intersection we identify the intersection point and return it but only if we are looking for mindistance*/
1881  {
1882  POINT2D theP;
1883 
1884  if (((A->x==C->x)&&(A->y==C->y))||((A->x==D->x)&&(A->y==D->y)))
1885  {
1886  theP.x = A->x;
1887  theP.y = A->y;
1888  }
1889  else if (((B->x==C->x)&&(B->y==C->y))||((B->x==D->x)&&(B->y==D->y)))
1890  {
1891  theP.x = B->x;
1892  theP.y = B->y;
1893  }
1894  else
1895  {
1896  theP.x = A->x+r*(B->x-A->x);
1897  theP.y = A->y+r*(B->y-A->y);
1898  }
1899  dl->distance=0.0;
1900  dl->p1=theP;
1901  dl->p2=theP;
1902  }
1903  return LW_TRUE;
1904 
1905  }
1906  lwerror("unspecified error in function lw_dist2d_seg_seg");
1907  return LW_FALSE; /*If we have come here something is wrong*/
1908 }
char * r
Definition: cu_in_wkt.c:24
int mode
Definition: measures.h:27
POINT2D p1
Definition: measures.h:25
double x
Definition: liblwgeom.h:312
#define DIST_MIN
Definition: measures.h:17
#define LW_FALSE
Definition: liblwgeom.h:62
#define LW_TRUE
Return types for functions with status returns.
Definition: liblwgeom.h:61
int lw_dist2d_pt_seg(const POINT2D *p, const POINT2D *A, const POINT2D *B, DISTPTS *dl)
lw_dist2d_comp from p to line A->B This one is now sending every occation to lw_dist2d_pt_pt Before i...
Definition: measures.c:2189
POINT2D p2
Definition: measures.h:26
double y
Definition: liblwgeom.h:312
char * s
Definition: cu_in_wkt.c:23
int twisted
Definition: measures.h:28
double distance
Definition: measures.h:24
#define DIST_MAX
Definition: measures.h:16
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:55
void lwerror(const char *fmt,...)
Write a notice out to the error handler.
Definition: lwutil.c:74

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