# HG changeset patch
# User jbe
# Date 1474720942 -7200
# Node ID bdbec73dc8fff92205566f625021d0c28ef17b5a
# Parent  868220477afb262621fc774208b98fed14f3f5a5
Improved accuracy for distance calculation to paths/polygons/outlines

diff -r 868220477afb -r bdbec73dc8ff latlon-v0007.c
--- a/latlon-v0007.c	Sat Sep 24 01:23:11 2016 +0200
+++ b/latlon-v0007.c	Sat Sep 24 14:42:22 2016 +0200
@@ -820,10 +820,15 @@
   double min_dist = INFINITY;   /* minimum distance */
   /* distance is zero if point is contained in cluster */
   if (pgl_point_in_cluster(point, cluster, false)) return 0;
-  /* calculate (approximate) square compression of meridians */
-  /* TODO: use more exact formula based on WGS-84 */
+  /* calculate approximate square compression of meridians */
   comp = cos((lat0 / 180.0) * M_PI);
   comp *= comp;
+  /* calculate exact square compression of meridians */
+  comp *= (
+    (1.0 - PGL_EPS2 * (1.0-comp)) *
+    (1.0 - PGL_EPS2 * (1.0-comp)) /
+    (PGL_SUBEPS2 * PGL_SUBEPS2)
+  );
   /* iterate over all entries */
   for (i=0; i<cluster->nentries; i++) {
     /* get properties of entry */