Fix lwgeom_tcpa distance computation for degenerate cases

git-svn-id: http://svn.osgeo.org/postgis/trunk@13628 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/liblwgeom/cunit/cu_measures.c b/liblwgeom/cunit/cu_measures.c
index 2213c59f020148510df253eccf1f5c037b9272e1..3d7bb9935c7939d429e4cb194988cfa8f1fd97bb 100644 (file)
--- a/liblwgeom/cunit/cu_measures.c
+++ b/liblwgeom/cunit/cu_measures.c
@@ -1099,6 +1099,17 @@ test_lwgeom_tcpa(void)
        ASSERT_DOUBLE_EQUAL(m, 1432291464.0);
        ASSERT_DOUBLE_EQUAL(dist, 0.0);
 
+       /* Tracks share a single point in time */
+
+       g1 = lwgeom_from_wkt("LINESTRINGM(0 0 0, 1 0 2)", LW_PARSER_CHECK_NONE);
+       g2 = lwgeom_from_wkt("LINESTRINGM(0 0 2, 1 0 3)", LW_PARSER_CHECK_NONE);
+       dist = -1;
+       m = lwgeom_tcpa(g1, g2, &dist);
+       lwgeom_free(g1);
+       lwgeom_free(g2);
+       ASSERT_DOUBLE_EQUAL(m, 2.0);
+       ASSERT_DOUBLE_EQUAL(dist, 1.0);
+
 }
 
 static void

diff --git a/liblwgeom/lwlinearreferencing.c b/liblwgeom/lwlinearreferencing.c
index 9665717ddbe6ff0cebaf954f2102287cdec8fe1a..09a12847677df20caa1d51e772a15a87009cfb9f 100644 (file)
--- a/liblwgeom/lwlinearreferencing.c
+++ b/liblwgeom/lwlinearreferencing.c
@@ -28,12 +28,19 @@ segment_locate_along(const POINT4D *p1, const POINT4D *p2, double m, double offs
                return LW_FALSE;
        }
 
-       /* We'll just can out on this degenerate case for now. 
-          Correct behavior is probably an mprop of 0.5? 
-          Still would have to deal with case of true p1==p2. */
        if( m1 == m2 ) 
        {
+               /* Degenerate case: same M on both points.
+                  If they are the same point we just return one of them. */
+               if ( p4d_same(p1,p2) )
+               {
+                       *pn = *p1;
+                       return LW_TRUE;
+               }
+               /* If the points are different we can out.
+                  Correct behavior is probably an mprop of 0.5? */
                lwerror("Zero measure-length line encountered!");
+               return LW_FALSE;
        }
 
        /* M is in range, new point to be generated. */
@@ -1083,16 +1090,6 @@ lwgeom_tcpa(const LWGEOM *g1, const LWGEOM *g2, double *mindist)
   tmin = FP_MAX(gbox1->mmin, gbox2->mmin);
   tmax = FP_MIN(gbox1->mmax, gbox2->mmax);
 
-  if ( tmax == tmin ) /* both exists only at a given time */
-  {
-    /*lwnotice("Inputs only exist both at a single time");*/
-    if ( mindist ) 
-    {
-      *mindist = lwgeom_mindistance3d(g1, g2);
-    }
-    return tmax;
-  }
-
   if ( tmax < tmin ) {
     lwerror("Inputs never exist at the same time");
     return -1;
@@ -1118,7 +1115,27 @@ lwgeom_tcpa(const LWGEOM *g1, const LWGEOM *g2, double *mindist)
   nmvals = uniq(mvals, nmvals);
 
   if ( nmvals < 2 )
-    return mvals[0]; /* there's a single time, must be that one... */
+  {{
+    /* there's a single time, must be that one... */
+    double t0 = mvals[0];
+    POINT4D p0, p1;
+    lwnotice("Inputs only exist both at a single time (%g)", t0);
+    if ( mindist )
+    {
+      if ( -1 == ptarray_locate_along_linear(l1->points, t0, &p0, 0) )
+      {
+        lwerror("Could not find point with M=%g on first geom", t0);
+        return -1;
+      }
+      if ( -1 == ptarray_locate_along_linear(l2->points, t0, &p1, 0) )
+      {
+        lwerror("Could not find point with M=%g on second geom", t0);
+        return -1;
+      }
+      *mindist = distance3d_pt_pt((POINT3D*)&p0, (POINT3D*)&p1);
+    }
+    return t0;
+  }}
 
   /*
    * For each consecutive pair of measures, compute time of closest point