diff --git a/examples/osgdem/DataSet.cpp b/examples/osgdem/DataSet.cpp
index 985ea7c22..660e1a6c1 100644
--- a/examples/osgdem/DataSet.cpp
+++ b/examples/osgdem/DataSet.cpp
@@ -738,6 +738,9 @@ void DataSet::Source::buildOverviews()
 }
 
 
+///////////////////////////////////////////////////////////////////////////////////////////////////////
+
+
 DataSet::DestinationTile::DestinationTile():
     _imagery_maxNumColumns(4096),
     _imagery_maxNumRows(4096),
@@ -755,6 +758,7 @@ DataSet::DestinationTile::DestinationTile():
     }
 }
 
+
 void DataSet::DestinationTile::computeMaximumSourceResolution(CompositeSource* sourceGraph)
 {
     for(CompositeSource::source_iterator itr(sourceGraph);itr.valid();++itr)
@@ -800,6 +804,43 @@ void DataSet::DestinationTile::computeMaximumSourceResolution(CompositeSource* s
     }
 }
 
+bool DataSet::DestinationTile::computeImageResolution(double& resX, double& resY)
+{
+    if (_imagery_maxSourceResolutionX!=0.0f && _imagery_maxSourceResolutionY!=0.0f &&
+        _imagery_maxNumColumns!=0 && _imagery_maxNumRows!=0)
+    {
+
+        unsigned int numColumnsAtFullRes = 1+(unsigned int)ceilf((_extents.xMax()-_extents.xMin())/_imagery_maxSourceResolutionX);
+        unsigned int numRowsAtFullRes = 1+(unsigned int)ceilf((_extents.yMax()-_extents.yMin())/_imagery_maxSourceResolutionY);
+        unsigned int texture_numColumns = osg::minimum(_imagery_maxNumColumns,numColumnsAtFullRes);
+        unsigned int texture_numRows    = osg::minimum(_imagery_maxNumRows,numRowsAtFullRes);
+        
+        resX = (_extents.xMax()-_extents.xMin())/(double)(texture_numColumns-1);
+        resY = (_extents.yMax()-_extents.yMin())/(double)(texture_numRows-1);
+        
+        return true;
+    }
+    return false;
+}
+
+bool DataSet::DestinationTile::computeTerrainResolution(double& resX, double& resY)
+{
+    if (_terrain_maxSourceResolutionX!=0.0f && _terrain_maxSourceResolutionY!=0.0f &&
+        _terrain_maxNumColumns!=0 && _terrain_maxNumRows!=0)
+    {
+        unsigned int numColumnsAtFullRes = 1+(unsigned int)ceilf((_extents.xMax()-_extents.xMin())/_terrain_maxSourceResolutionX);
+        unsigned int numRowsAtFullRes = 1+(unsigned int)ceilf((_extents.yMax()-_extents.yMin())/_terrain_maxSourceResolutionY);
+        unsigned int dem_numColumns = osg::minimum(_terrain_maxNumColumns,numColumnsAtFullRes);
+        unsigned int dem_numRows    = osg::minimum(_terrain_maxNumRows,numRowsAtFullRes);
+
+        resX = (_extents.xMax()-_extents.xMin())/(double)(dem_numColumns-1);
+        resY = (_extents.yMax()-_extents.yMin())/(double)(dem_numRows-1);
+        
+        return true;
+    }
+    return false;
+}
+
 void DataSet::DestinationTile::allocate()
 {
 
@@ -1281,6 +1322,50 @@ void DataSet::DestinationTile::readFrom(CompositeSource* sourceGraph)
     }
 }
 
+void DataSet::DestinationTile::addRequiredResolutions(CompositeSource* sourceGraph)
+{
+    for(CompositeSource::source_iterator itr(sourceGraph);itr.valid();++itr)
+    {
+        Source* source = itr->get();
+        if (_imagery.valid() && source->getType()==Source::IMAGE)
+        {
+            double resX, resY;
+            if (computeImageResolution(resX,resY))
+            {
+                source->addRequiredResolution(resX,resY);
+            }
+        }
+        if (_terrain.valid() && source->getType()==Source::HEIGHT_FIELD)
+        {
+            double resX, resY;
+            if (computeTerrainResolution(resX,resY))
+            {
+                source->addRequiredResolution(resX,resY);
+            }
+        }
+    }
+}
+
+
+void DataSet::CompositeDestination::addRequiredResolutions(CompositeSource* sourceGraph)
+{
+    // handle leaves
+    for(TileList::iterator titr=_tiles.begin();
+        titr!=_tiles.end();
+        ++titr)
+    {
+        (*titr)->addRequiredResolutions(sourceGraph);
+    }
+    
+    // handle chilren
+    for(ChildList::iterator citr=_children.begin();
+        citr!=_children.end();
+        ++citr)
+    {
+        (*citr)->addRequiredResolutions(sourceGraph);
+    }
+}
+
 void DataSet::CompositeDestination::readFrom(CompositeSource* sourceGraph)
 {
     // handle leaves
@@ -1602,6 +1687,12 @@ void DataSet::updateSourcesForDestinationGraphNeeds()
         }
     }
     
+    // compute the resolutions of the source that are required.
+    {
+        _destinationGraph->addRequiredResolutions(_sourceGraph.get());
+    }
+
+
     // do sampling of data to required values.
     {
         for(CompositeSource::source_iterator itr(_sourceGraph.get());itr.valid();++itr)
diff --git a/examples/osgdem/DataSet.h b/examples/osgdem/DataSet.h
index b87ca0805..9569e422e 100644
--- a/examples/osgdem/DataSet.h
+++ b/examples/osgdem/DataSet.h
@@ -22,6 +22,8 @@
 
 #include <osgTerrain/CoordinateSystem>
 
+#include <set>
+
 #include <gdal_priv.h>
 
 class DataSet : public osg::Referenced
@@ -188,6 +190,7 @@ class DataSet : public osg::Referenced
             SourceData* getSourceData() { return _sourceData.get(); }
             
             void loadSourceData();
+
             
             bool needReproject(const osgTerrain::CoordinateSystem* cs) const;
 
@@ -196,6 +199,18 @@ class DataSet : public osg::Referenced
             Source* doReproject(const std::string& filename, osgTerrain::CoordinateSystem* cs, double targetResolution=0.0) const;
            
             void buildOverviews();
+            
+            
+            typedef std::pair<double,double> ResolutionPair;
+            typedef std::set<ResolutionPair> ResolutionList;
+            
+            void addRequiredResolution(double resX, double resY) { _requiredResolutions.insert(ResolutionPair(resX,resY)); }
+            
+            void setRequiredResolutions(ResolutionList& resolutions) { _requiredResolutions = resolutions; }
+            
+            ResolutionList& getRequiredResolutions() { return _requiredResolutions; }
+            
+            const ResolutionList& getRequiredResolutions() const { return _requiredResolutions; }
 
         protected:
         
@@ -211,6 +226,8 @@ class DataSet : public osg::Referenced
             ParameterPolicy                             _geoTransformPolicy;
             
             osg::ref_ptr<SourceData>                    _sourceData;
+            
+            ResolutionList                              _requiredResolutions;
                 
         };
         
@@ -383,13 +400,6 @@ class DataSet : public osg::Referenced
                     inline bool advance()
                     {
                         return advanceToNextChild(*_composite,_index);
-                        
-//                         if (_index+1 < (int)_composite->_children.size())
-//                         {
-//                             ++_index;
-//                             return valid();
-//                         }
-//                         return false;
                     }
 
                     inline bool isActive(const CompositeSource& composite,int index)
@@ -609,8 +619,13 @@ class DataSet : public osg::Referenced
             
             void computeMaximumSourceResolution(CompositeSource* sourceGraph);
 
+            bool computeImageResolution(double& resX, double& resY);
+            bool computeTerrainResolution(double& resX, double& resY);
+
             void allocate();
             
+            void addRequiredResolutions(CompositeSource* sourceGraph);
+
             void readFrom(CompositeSource* sourceGraph);
             
             void equalizeCorner(Position position);
@@ -648,6 +663,8 @@ class DataSet : public osg::Referenced
         {
         public:
             
+            void addRequiredResolutions(CompositeSource* sourceGraph);
+            
             void readFrom(CompositeSource* sourceGraph);
 
             void equalizeBoundaries();