--- a/gnv-artifacts/src/main/java/de/intevation/gnv/math/XYColumn.java	Wed Dec 23 09:45:40 2009 +0000
+++ b/gnv-artifacts/src/main/java/de/intevation/gnv/math/XYColumn.java	Wed Dec 23 12:20:25 2009 +0000
@@ -2,6 +2,19 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Collections;
+
+import org.apache.commons.math.analysis.interpolation.SplineInterpolator;
+import org.apache.commons.math.analysis.interpolation.UnivariateRealInterpolator;
+
+import org.apache.commons.math.analysis.polynomials.PolynomialSplineFunction;
+
+import org.apache.commons.math.analysis.UnivariateRealFunction;
+
+import org.apache.commons.math.MathException;
+import org.apache.commons.math.FunctionEvaluationException;
+
+import org.apache.log4j.Logger;
 
 /**
  * @author Ingo Weinzierl <ingo.weinzierl@intevation.de>
@@ -9,25 +22,98 @@
  */
 public class XYColumn
 extends      Point2d
+implements   UnivariateRealFunction
 {
+    private static Logger log = Logger.getLogger(Interpolation2D.class);
+
     protected List<HeightValue> values;
 
+    protected transient UnivariateRealFunction curve;
+
     public XYColumn() {
+        values = new ArrayList<HeightValue>();
     }
 
     public XYColumn(double x, double y, int i, int j) {
         super(x, y, i, j);
+        values = new ArrayList<HeightValue>();
     }
 
     public void add(HeightValue value) {
-        if (values == null) {
-            values = new ArrayList<HeightValue>();
-        }
         values.add(value);
     }
 
     public List<HeightValue> getValues() {
         return values;
     }
+
+    public double value(double depth) {
+        try {
+            if (curve != null) {
+                return curve.value(depth);
+            }
+        }
+        catch (FunctionEvaluationException fee) {
+            log.error("evaluation failed", fee);
+        }
+
+        return Double.NaN;
+    }
+
+    public void prepare(XYDepth xyDepth) {
+        int N = values.size();
+        if (curve == null && N > 0) {
+            if (N == 1) {
+                // only one value -> constant function
+                curve = new ConstantFunction(values.get(0).v);
+            }
+            else { // more than on value
+                double depth = xyDepth.depth(this);
+                Collections.sort(values, HeightValue.INV_Z_COMPARATOR);
+
+                // if there is no value at 0 repeat first value
+                HeightValue first = values.get(0);
+                if (first.z < 0d) {
+                    values.add(0, new HeightValue(0d, first.z, first.k-1));
+                }
+
+                // if there is no value at depth repeat last value
+                HeightValue last = values.get(N-1);
+                if (last.z > depth) {
+                    values.add(new HeightValue(depth, last.z, last.k+1));
+                }
+                N = values.size();
+                if (N < 3) { // interpolate linear
+                    first = values.get(0);
+                    last  = values.get(N-1);
+                    curve = new LinearFunction.Univariate(
+                        first.z, first.v,
+                        last.z,  last.v);
+                }
+                else { // higher degree interpolation
+                    double [] z = new double[N];
+                    double [] v = new double[N];
+                    for (int i = 0; i < N; ++i) {
+                        HeightValue h = values.get(i);
+                        z[i] = h.z;
+                        v[i] = h.v;
+                    }
+                    try {
+                        curve = getInterpolator().interpolate(z, v);
+                    }
+                    catch (MathException me) {
+                        log.error("interpolation failed", me);
+                    }
+                }
+            }
+        }
+        else {
+            log.error("no points for interpolation");
+        }
+    }
+
+    protected UnivariateRealInterpolator getInterpolator() {
+        return new SplineInterpolator();
+    }
 }
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