[UW-GIS-L] IDW problems in Workstation (VBA Solution)

[David Finlayson]

When AML fails, turn to your last resort...VBA:

Sub IDW()
    ' Set the two variables to fit data
    Dim sFieldName As String
    sFieldName = "height"  'Field name used in interpolation
    Dim CellSize As Double
    CellSize = 60  'Cell size for output raster

   ' Get the point and barrier shapefiles
    Dim pWorkspaceFactory As IWorkspaceFactory
    Set pWorkspaceFactory = New ShapefileWorkspaceFactory
   
    Dim pFeatureWorkspace As IFeatureWorkspace
    Set pFeatureWorkspace = _
        pWorkspaceFactory.OpenFromFile("C:\Your\Directory", 0)
   
    Dim pFeaClsPoints As IFeatureClass
    Set pFeaClsPoints = 
pFeatureWorkspace.OpenFeatureClass("points_shapefile")
   
    Dim pFeaClsBarriers As IFeatureClass
    Set pFeaClsBarriers = 
pFeatureWorkspace.OpenFeatureClass("barriers_shapefile")
   
    ' Create FeatureClassDescriptor using a value field
    Dim pFDescr As IFeatureClassDescriptor
    Set pFDescr = New FeatureClassDescriptor
    pFDescr.Create pFeaClsPoints, Nothing, sFieldName

    ' Create RasterInterpolationOp object
    Dim pIntOp As IInterpolationOp
    Set pIntOp = New RasterInterpolationOp

    ' Set cell size for output raster. The extent of the output raster is
    ' defualted to as same as input. The output working directory uses 
default
    Dim pEnv As IRasterAnalysisEnvironment
    Set pEnv = pIntOp
    pEnv.SetCellSize esriRasterEnvValue, CellSize

    ' Create raster radius using variable distance
    Dim pRadius As IRasterRadius
    Set pRadius = New RasterRadius
    pRadius.SetVariable 3

    ' Using FeatureClassDescriptor as an input to the IInterpolationOp and
    ' Perform the interpolation
    Dim pOutRaster As IRaster
    Set pOutRaster = pIntOp.IDW(pFDescr, 2, pRadius, pFeaClsBarriers)

End Sub

I adapted this solution from:

http://arcobjectsonline.esri.com/ArcObjectsOnline/Samples/Spatial%20Analyst/FeatureClassDescriptor.htm

It's only 44 times as long as the AML code to do the same thing. Too bad 
the AML didn't work :(

Cheers,

David

David Finlayson wrote:

> I am trying to script a cross-validation analysis using IDW with 
> barriers (hence, I cannot use Geostatistical Analyst).
>
> When I issue the command:
>
> > outgrid = idw(point.gen, #, #, 2, RADIUS, 52800, 3, 52800)
>
> The interpolation proceeds without error. However, when I include the 
> barriers I get the following error:
>
> > outgrid = idw(point.gen, #, barrier.gen, 2, RADIUS, 52800, 3, 52800)
> Unknown input point type: 1
>
> The error is in the barrier file (since IDW worked without the 
> barriers) or it's a bug in IDW. I created the barriers as a coverage 
> and then dumped them to the file with UNGENERATE, so presumably it's 
> in the proper format. I have tried selectively removing lines from the 
> barrier file (down to just one line) with the same error results.
>
> Interestingly enough, the interpolation with barriers works fine from 
> Spatial Analyst's GUI (but I don't want to manually create 100's of 
> IDW grids!)
>
> Has anyone else run into this?
>
> David
>

-- 
David Finlayson
Marine Geology & Geophysics
School of Oceanography
Box 357940
University of Washington
Seattle, WA  98195-7940
USA

Office: Marine Sciences Building, Room 112
Phone: (206) 616-9407
Web: http://students.washington.edu/dfinlays