--- a/flys-artifacts/src/main/java/de/intevation/flys/artifacts/states/WaterlevelGroundDifferences.java	Thu Jan 24 15:04:01 2013 +0100
+++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/states/WaterlevelGroundDifferences.java	Thu Jan 24 16:09:46 2013 +0100
@@ -4,11 +4,14 @@
 
 import org.apache.log4j.Logger;
 
+import de.intevation.flys.artifacts.FLYSArtifact;
+
 import de.intevation.artifacts.Artifact;
 import de.intevation.artifacts.CallContext;
 
 import de.intevation.artifacts.common.utils.XMLUtils;
 
+import de.intevation.artifactdatabase.data.StateData;
 import de.intevation.artifactdatabase.ProtocolUtils;
 
 
@@ -28,20 +31,16 @@
         Logger.getLogger(WaterlevelGroundDifferences.class);
 
 
-
-    @Override
     protected String getLowerField() {
         return LOWER_FIELD;
     }
 
 
-    @Override
     protected String getUpperField() {
         return UPPER_FIELD;
     }
 
 
-    @Override
     protected String getStepField() {
         return DIFF_FIELD;
     }
@@ -122,5 +121,37 @@
 
         return item;
     }
+
+    @Override
+    public boolean validate(Artifact artifact)
+    throws IllegalArgumentException
+    {
+        FLYSArtifact flys = (FLYSArtifact) artifact;
+
+        StateData dFrom = getData(flys, getLowerField());
+        StateData dTo   = getData(flys, getUpperField());
+        StateData dStep = getData(flys, getStepField());
+
+        String fromStr = dFrom != null ? (String) dFrom.getValue() : null;
+        String toStr   = dTo   != null ? (String) dTo.getValue()   : null;
+        String stepStr = dStep != null ? (String) dStep.getValue() : null;
+
+        if (fromStr == null || toStr == null || stepStr == null) {
+            throw new IllegalArgumentException("error_empty_state");
+        }
+
+        try {
+            double from = Double.parseDouble(fromStr);
+            double to   = Double.parseDouble(toStr);
+            double step = Double.parseDouble(stepStr);
+
+            double[] minmax = getMinMax(flys);
+
+            return validateBounds(minmax[0], minmax[1], from, to, step);
+        }
+        catch (NumberFormatException nfe) {
+            throw new IllegalArgumentException("error_invalid_double_value");
+        }
+    }
 }
 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf-8 :