--- a/gnv-artifacts/src/main/java/de/intevation/gnv/math/AreaInterpolation.java	Tue Jan 19 12:45:51 2010 +0000
+++ b/gnv-artifacts/src/main/java/de/intevation/gnv/math/AreaInterpolation.java	Tue Jan 19 14:06:10 2010 +0000
@@ -9,12 +9,15 @@
 
 import java.io.Serializable;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
 import org.apache.log4j.Logger;
 
+import de.intevation.gnv.utils.GridIndex;
+
 /**
  *  @author Sascha L. Teichmann (sascha.teichmann@intevation.de)
  */
@@ -58,32 +61,45 @@
             return false;
         }
 
-        double [] buffer = Interpolation2D.calculateBuffer(points);
+        int W = samples.width;
+        int H = samples.height;
+
+        double cellWidth  = boundingBox.getWidth()  / W;
+        double cellHeight = boundingBox.getHeight() / H;
+        Envelope gridEnvelope = new Envelope(boundingBox);
+
+        gridEnvelope.expandBy(2d*cellWidth, 2d*cellWidth);
+
+        ArrayList<Point2d>relevantPoints =
+            new ArrayList<Point2d>();
+
+        for (int i = points.size()-1; i >= 0; --i) {
+            if (gridEnvelope.contains(points.get(i))) {
+                relevantPoints.add(points.get(i));
+            }
+        }
+
+        double [] buffer = Interpolation2D.calculateBuffer(relevantPoints);
         double dxMax = buffer[0];
         double dyMax = buffer[1];
 
         Quadtree spatialIndex = new Quadtree();
 
-        for (int i = points.size()-1; i >= 0; --i) {
-            Point2d p = points.get(i);
+        for (int i = relevantPoints.size()-1; i >= 0; --i) {
+            Point2d p = relevantPoints.get(i);
             spatialIndex.insert(p.envelope(), p);
         }
 
-        int W = samples.width;
-        int H = samples.height;
-
-        double cellWidth  = boundingBox.getWidth()  / W;
-        double cellHeight = boundingBox.getHeight() / H;
-
         if (debug) {
-            log.debug("width:  " + boundingBox.getWidth());
-            log.debug("height:  " + boundingBox.getHeight());
+            log.debug("points: "        + relevantPoints.size());
+            log.debug("width:  "        + boundingBox.getWidth());
+            log.debug("height:  "       + boundingBox.getHeight());
             log.debug("sample width:  " + W);
             log.debug("sample height: " + H);
-            log.debug("cell width:  " + cellWidth);
-            log.debug("cell height: " + cellHeight);
-            log.debug("buffer x: " + dxMax);
-            log.debug("buffer y: " + dyMax);
+            log.debug("cell width:  "   + cellWidth);
+            log.debug("cell height: "   + cellHeight);
+            log.debug("buffer x: "      + dxMax);
+            log.debug("buffer y: "      + dyMax);
         }
 
         Envelope     queryBuffer = new Envelope();
@@ -97,8 +113,8 @@
         double minX = boundingBox.getMinX();
         double minY = boundingBox.getMinY();
 
-        int row = 0;
-        for (int j = 0; j < H; ++j, row += W) {
+        int row = (H-1)*W;
+        for (int j = 0; j < H; ++j, row -= W) {
             double y = j*cellHeight + 0.5d*cellHeight + minY;
             double x = 0.5d*cellWidth + minX;
             for (int i = 0; i < W; ++i, x += cellWidth) {