Ticket #233: truecircles.diff

src/org/openstreetmap/josm/actions/AlignInCircleAction.java

@@ -52 +52 @@
                 // Node "avn" now is central to all selected nodes.
 
                 // Now calculate the average distance to each node from the
-                // centre.
-                double avdist = 0;
-                for (Node n : nodes)
-                        avdist += Math.sqrt(avn.eastNorth.distance(n.eastNorth));
+                // centre.  This method is ok as long as distances are short 
+                // relative to the distance from the N or S poles.
+                double distances[] = new double[nodes.size()];
+                double avdist = 0, latd, lond;
+                double lonscale = Math.cos(avn.coor.lat() * Math.PI/180.0);
+                lonscale = lonscale * lonscale;
+                int i = 0;
+                for (Node n : nodes) {
+                        latd = n.coor.lat() - avn.coor.lat();
+                        lond = n.coor.lon() - avn.coor.lon();
+                        distances[i] = Math.sqrt(latd * latd + lonscale * lond * lond);
+                        avdist += distances[i++];
+                }
                 avdist = avdist / nodes.size();
 
                 Collection<Command> cmds = new LinkedList<Command>();
-                // Move each node to that distance from the centre.
+                // Move each node to that distance from the centre.
+                i = 0;
                 for (Node n : nodes) {
                         double dx = n.eastNorth.east() - avn.eastNorth.east();
-                        double dy = n.eastNorth.north() - avn.eastNorth.north();
-                        double dist = Math.sqrt(avn.eastNorth.distance(n.eastNorth));
+                        double dy = n.eastNorth.north() - avn.eastNorth.north();
+                        double dist = distances[i++];
                         cmds.add(new MoveCommand(n, (dx * (avdist / dist)) - dx, (dy * (avdist / dist)) - dy));
                 }