--- a/flys-artifacts/src/main/java/de/intevation/flys/artifacts/model/WstValueTable.java	Fri Jun 10 14:24:15 2011 +0000
+++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/model/WstValueTable.java	Fri Jun 10 15:59:47 2011 +0000
@@ -494,28 +494,36 @@
     }
 
     public QPosition interpolate(
-        double    q,
-        double    referenceKm,
-        double [] kms,
-        double [] ws,
-        double [] qs
+        double      q,
+        double      referenceKm,
+        double []   kms,
+        double []   ws,
+        double []   qs,
+        Calculation errors
     ) {
-        return interpolate(q, referenceKm, kms, ws, qs, 0, kms.length);
+        return interpolate(
+            q, referenceKm, kms, ws, qs, 0, kms.length, errors);
     }
 
     public QPosition interpolate(
-        double    q,
-        double    referenceKm,
-        double [] kms,
-        double [] ws,
-        double [] qs,
-        int       startIndex,
-        int       length
+        double      q,
+        double      referenceKm,
+        double []   kms,
+        double []   ws,
+        double []   qs,
+        int         startIndex,
+        int         length,
+        Calculation errors
     ) {
         QPosition qPosition = getQPosition(referenceKm, q);
 
         if (qPosition == null) {
             // we cannot locate q at km
+            Arrays.fill(ws, Double.NaN);
+            Arrays.fill(qs, Double.NaN);
+            if (errors != null) {
+                errors.addProblem(referenceKm, "cannot find q");
+            }
             return null;
         }
 
@@ -524,15 +532,24 @@
         int R1 = rows.size()-1;
 
         for (int i = startIndex, end = startIndex+length; i < end; ++i) {
-            kmKey.km = kms[i];
 
+            if (Double.isNaN(qs[i] = getQ(qPosition, kms[i]))) {
+                if (errors != null) {
+                    errors.addProblem(kms[i], "cannot find q");
+                }
+                ws[i] = Double.NaN;
+                continue;
+            }
+
+            kmKey.km = kms[i];
             int rowIndex = Collections.binarySearch(rows, kmKey);
 
-            qs[i] = getQ(qPosition, kms[i]);
-
             if (rowIndex >= 0) {
                 // direct row match
-                ws[i] = rows.get(rowIndex).getW(qPosition);
+                if (Double.isNaN(ws[i] = rows.get(rowIndex).getW(qPosition))
+                && errors != null) {
+                    errors.addProblem(kms[i], "cannot find w");
+                }
                 continue;
             }
 
@@ -540,13 +557,19 @@
 
             if (rowIndex < 1 || rowIndex >= R1) {
                 // do not extrapolate
+                if (errors != null) {
+                    errors.addProblem(kms[i], "cannot find km");
+                }
                 ws[i] =  Double.NaN;
                 continue;
             }
             Row r1 = rows.get(rowIndex-1);
             Row r2 = rows.get(rowIndex);
 
-            ws[i] = r1.getW(r2, kms[i], qPosition);
+            if (Double.isNaN(ws[i] = r1.getW(r2, kms[i], qPosition))
+            && errors != null) {
+                errors.addProblem(kms[i], "cannot find w");
+            }
         }
 
         return qPosition;