Getting the Elvation from a surface raster

[JosephSheffield]

I'm trying to get the elevation value from a raster along a specific line.  I'm passing in the raster layer as a IRasterLayer and the feature class as IFeatureLayer.  I know I have to the raster from a IRasterLayer data type to an ISurface data type.  Does anyone know the way to do so?

Here is the relevant code block:

public void GetThicknessData(IRasterLayer rAlamoSurface, IFeatureLayer fThicknessProfile)
          {
              try
              {
                  IFeature fProfile = fThicknessProfile.FeatureClass.GetFeature(11);
                  IPointCollection pPointCollection = null;
                  IPolyline pPolyLine = null;
                  IGeometry pGeom = null;
                  Double dCellSize = 30;
                  IRasterSurface pRasterSurface = rAlamoSurface as IRasterSurface;

                  ISurface pSurface = pRasterSurface as ISurface;
                  pPolyLine = fProfile.Shape as IPolyline;
                  pPointCollection = pPolyLine as IPointCollection;
                  pGeom = pPointCollection as IGeometry;

                  IPoint tmpPt = null;
                  IPoint tmpPt2 = null;
                  IPoint stepPoint = null;
                  int ArrayCtr, loopCount, ptCtr, sgCtr;

                  ArrayCtr = 0;
                  double[] XArray = new double[1000];
                  double[] YArray = new double[1000];
                  double[] ElevArray = new double[1000];
                  double pElev, dX, dY, segLength, runStep, riseStep, lastPointX, lastPointY, gridNoData;
                  gridNoData = -99999;

                  tmpPt = pPointCollection.get_Point(0);
                  XArray[ArrayCtr] = tmpPt.X;
                  YArray[ArrayCtr] = tmpPt.Y;
                 
                  pElev = pSurface.GetElevation(tmpPt);
                  if (pElev != gridNoData)
                  {
                      ElevArray[ArrayCtr] = pElev;
                  }

                  for (ptCtr = 1; ptCtr <= pPointCollection.PointCount - 1; ptCtr++)
                  {
                      tmpPt.X = pPointCollection.get_Point(ptCtr - 1).X;
                      tmpPt.Y = pPointCollection.get_Point(ptCtr - 1).Y;
                      tmpPt2.X = pPointCollection.get_Point(ptCtr).X;
                      tmpPt2.Y = pPointCollection.get_Point(ptCtr).Y;

                      dX = (tmpPt2.X - tmpPt.X);
                      dY = (tmpPt2.Y - tmpPt.Y);


                      segLength = Math.Sqrt(Math.Pow(dX, 2) + Math.Pow(dY, 2));
                      runStep = dCellSize * (dX) / segLength;
                      riseStep = dCellSize * (dY) / segLength;

                      loopCount = (int)Math.Round((segLength * 10000) / (dCellSize * 10000));
                      //*10000 because the cell size is so small it causes a divide by zero error.
                      lastPointX = tmpPt.X;
                      lastPointY = tmpPt.Y;

                      for (sgCtr = 1; sgCtr <= loopCount; sgCtr++)
                      {
                          ArrayCtr = ArrayCtr + 1;
                          stepPoint.X = lastPointX + runStep;
                          stepPoint.Y = lastPointY + riseStep;
                          XArray[ArrayCtr] = stepPoint.X;
                          YArray[ArrayCtr] = stepPoint.Y;
                          pElev = pSurface.GetElevation(stepPoint);

                          if (pElev != gridNoData)
                          {
                              ElevArray[ArrayCtr] = pElev;
                              lastPointX = stepPoint.X;
                              lastPointY = stepPoint.Y;
                          }
                      }

                      if ((segLength * 10000) % (dCellSize * 10000) != 0)
                      {
                          ArrayCtr = ArrayCtr + 1;
                          stepPoint.X = lastPointX + runStep;
                          stepPoint.Y = lastPointY + riseStep;
                          XArray[ArrayCtr] = stepPoint.X;
                          YArray[ArrayCtr] = stepPoint.Y;
                          pElev = pSurface.GetElevation(stepPoint);
                          if (pElev != gridNoData)
                          {
                              ElevArray[ArrayCtr] = pElev;
                          }
                      }
                  }
              }


              catch (Exception ex)
              {
                  MessageBox.Show(ex.Message);
              }
             }

[JosephSheffield]

So I've figure out part of the problem.  I can get the raster to a IRasterBand class, but I can't figure out the code/syntax to get the raster to a IRasterSurface class:  Here is the code:

 

IFeature fProfile = fThicknessProfile.FeatureClass.GetFeature(11);
                  IPointCollection pPointCollection = null;
                  IPolyline pPolyLine = null;
                  IGeometry pGeom = null;
                  Double dCellSize = 30;
                  IRasterBandCollection pRasterBands = null;
                  pRasterBands = rAlamoSurface.Raster as IRasterBandCollection;
                  IRasterBand pRasterBand = pRasterBands.Item(0);
                  IRasterSurface pRasterSurface = null;
                  //I get the error here....trying to cast an IRasterBand to an IRasterSurface
                  pRasterSurface.RasterBand = pRasterBand as IRasterSurface;
                  //I've found other VB.net references that use:
                  //pRasterSurface.RasterBand = pRasterBand

Thanks in advance for anyone who can help me.

[NeilClemmons]

If you open the developer help to the ISurface.GetElevation method topic you'll find a link to the Get Elevation developer sample.

[JosephSheffield]

The Developer Help does not include sample code that helps me figure out how to cast the IRasterBand to IRasterSurface.  I have the code working in VBA for Arc 9.3, I'm migrating it over to Arc 10. Every resource I can finds leads me to believe that the correct syntax is:

pRasterSurface.RasterBand = pRasterBand

However, when I run the code nothing is passed into pRasterSurface.  I get a null value.

[NeilClemmons]

The example link is at the bottom of the page:

http://resources.esri.com/help/9.3/arcgisserver/apis/arcobjects/esrigeodatabase/ISurface_GetElevatio...

[JosephSheffield]

I'm using ArcGIS 10.  I've used the same methodology as with the code I have for VBA in ArcGIS 9.3.  

Based on the link I've tired:

pRasterSurface.RasterBand = pRasterBands.Item(0);

And I still get an error.

[NeilClemmons]

You don't need to use IRasterSurface at all.  All you need is an ISurface reference so that you can call ISurface.GetElevation().  The example in the link above shows how to get the ISurface reference from the IRasterLayer reference.

[JosephSheffield]

In the same code I see two ways of doing it:

pSurface = GetSurfaceFromLayer(pLayer.Name;

or

pRasterSurface.RasterBand = pRasterBands.Item(0);

In both cases I get an error.  I don't see a method (GetSurfaceFromLayer) on the pSurface. 

The error I am getting is "Object reference not set to an instance of an object."

[NeilClemmons]

GetSurfaceFromLayer is not a method on ISurface; it is a function provided in the example that will return an ISurface reference given a layer name.  Here is the same function translated to VB.NET.  Pass in a reference to the raster layer and it will return the surface. 

        ''' <summary>
        ''' Returns the surface from the layer with the specified name.
        ''' </summary>
        ''' <param name="layer">The layer whose surface will be returned</param>
        ''' <returns></returns>
        ''' <remarks></remarks>
        Public Shared Function GetSurfaceFromLayer(ByVal layer As ILayer) As ISurface
            ' Get the actual surface from the layer.
            If TypeOf layer Is ITinLayer Then
                ' QI
                Dim tinLayer As ITinLayer = CType(layer, ITinLayer)

                ' Return surface from TIN layer.
                Return CType(tinLayer.Dataset, ISurface)
            ElseIf TypeOf layer Is IRasterLayer Then
                ' QI
                Dim rasterLayer As IRasterLayer = CType(layer, IRasterLayer)

                ' Get surface from 3d extension on layer.
                Dim layerExtensions As ILayerExtensions = CType(rasterLayer, ILayerExtensions)
                For i As Integer = 0 To layerExtensions.ExtensionCount - 1
                    Dim dddProperties As I3DProperties = CType(layerExtensions.Extension(i), I3DProperties)
                    If Not dddProperties Is Nothing Then
                        If dddProperties.BaseOption = esriBaseOption.esriBaseSurface Then
                            If Not dddProperties.BaseSurface Is Nothing Then
                                Return CType(dddProperties.BaseSurface, ISurface)
                            End If
                        End If
                        Exit For
                    End If
                Next i

                ' Get surface from raster band collection.
                Dim rasterBandCollection As IRasterBandCollection = CType(rasterLayer.Raster, IRasterBandCollection)
                Dim rasterBand As IRasterBand = rasterBandCollection.Item(0)
                Dim rasterSurface As IRasterSurface = New RasterSurface
                rasterSurface.RasterBand = rasterBand

                Return CType(rasterSurface, ISurface)
            Else
                Return Nothing
            End If
        End Function

[JosephSheffield]

I see that now.

However, the step that gives me an error each time is:

 rasterSurface.RasterBand = rasterBand;

In every example of code I can find I see this same step and I get the same error each time.