[vtkusers] Problem getting correct results with vtkProjectedTerrainPath

[Elvis Dowson]

Nope, tried using vtkUnstructuredGrid but I get the following error,  
saying vtkImageData is required by btkProjectedTerrainPath...

ERROR: In /Users/elvis/Tool/vtk-5.x/src/VTK/Filtering/ 
vtkDemandDrivenPipeline.cxx, line 828
vtkStreamingDemandDrivenPipeline (0x6238910): Input for connection  
index 0 on input port index 1 for algorithm  
vtkProjectedTerrainPath(0x6237cc0) is of type vtkStructuredGrid, but a  
vtkImageData is required.