[GRASS-SVN] r32957 - grass/branches/develbranch_6/vector/v.surf.idw

[svn_grass at osgeo.org]

Author: benducke
Date: 2008-08-21 05:05:13 -0400 (Thu, 21 Aug 2008)
New Revision: 32957

Modified:
   grass/branches/develbranch_6/vector/v.surf.idw/description.html
   grass/branches/develbranch_6/vector/v.surf.idw/main.c
Log:
This update adds support for the "power parameter" to v.surf.idw.
That parameter is a standard part of the IDW algorithm and describes the
fall-off in weight of a data point with spatial distance from the cell to be
interpolated.

Modified: grass/branches/develbranch_6/vector/v.surf.idw/description.html
===================================================================
--- grass/branches/develbranch_6/vector/v.surf.idw/description.html	2008-08-21 09:03:44 UTC (rev 32956)
+++ grass/branches/develbranch_6/vector/v.surf.idw/description.html	2008-08-21 09:05:13 UTC (rev 32957)
@@ -47,6 +47,14 @@
 sites closest to the centre of the cell will be interpolated).</p>
 
 <P>
+The <EM>power=</EM> parameter defines an exponential distance weight.
+Greater values assign greater influence to values closer to the
+point to be interpolated. The interpolation function peaks sharply over
+the given data points for 0 < <EM>p</EM> < 1 and more smoothly for
+larger values. The default value for the power parameter is 2.  
+</p>
+
+<P>
 By setting <EM>npoints=1</EM>, the module can be used 
 to calculate raster Voronoi diagrams (Thiessen polygons).</p>
 

Modified: grass/branches/develbranch_6/vector/v.surf.idw/main.c
===================================================================
--- grass/branches/develbranch_6/vector/v.surf.idw/main.c	2008-08-21 09:03:44 UTC (rev 32956)
+++ grass/branches/develbranch_6/vector/v.surf.idw/main.c	2008-08-21 09:05:13 UTC (rev 32957)
@@ -64,9 +64,10 @@
     double dist;
     double sum1, sum2, interp_value;
     int n, field;
+    double p;
     struct
     {
-	struct Option *input, *npoints, *output, *dfield, *col;
+	struct Option *input, *npoints, *power, *output, *dfield, *col;
     } parm;
     struct cell_list
     {
@@ -97,6 +98,13 @@
     parm.npoints->description = _("Number of interpolation points");
     parm.npoints->answer = "12";
 
+    parm.power = G_define_option();
+    parm.power->key = "power";
+    parm.power->type = TYPE_DOUBLE;
+    parm.power->answer = "2.0";
+    parm.power->description = 
+    	_("Power parameter; greater values assign greater influence to closer points");
+
     parm.dfield = G_define_standard_option(G_OPT_V_FIELD);
     parm.dfield->description =
 	_("If set to 0, z coordinates are used (3D vector only)");
@@ -135,8 +143,9 @@
     list =
 	(struct list_Point *)G_calloc((size_t) search_points,
 				      sizeof(struct list_Point));
+				      
+    p = atof ( parm.power->answer );
 
-
     /* get the window, dimension arrays */
     G_get_window(&window);
 
@@ -375,8 +384,8 @@
 		sum2 = 0.0;
 		for (n = 0; n < nsearch; n++) {
 		    if ((dist = list[n].dist)) {
-			sum1 += list[n].z / dist;
-			sum2 += 1.0 / dist;
+			sum1 += list[n].z / pow ( dist, p );
+			sum2 += 1.0 / pow ( dist, p );
 		    }
 		    else {
 			/* If one site is dead on the centre of the cell, ignore