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ET GeoWizards Scripting

Split a Polygon dataset with Polylines - How to do it?

A common question posted to the ArcGIS forums and to our support line. There is a tool available in ArcMap that allows the user to draw a polyline which will divide the selected polygon. ET GeoTools has a tool that will divide the polygons using selected polylines from a polyline layer. The problem with these tools is that only the polylines that have both their ends outside of a polygon will be used for splitting.

How should we split a polygon representing a catchment area with the rivers inside this catchment?  One possible solution is described below and can be achieved using ET GeoWizards scripting with few lines of code.

Step 1: Convert your polygons to polylines
Step 2: Merge the polylines derived in Step 1 with the polylines to be used for splitting
Step 3: Clean the merged polylines
Step 4: Build polygons from the cleaned polylines
Step 5: Transfer the attributes from the original polygons to the newly created ones

This is achievable with the functions available in ET GeoWizards together with some standard ArcGIS functions, but each of the steps needs to be performed via the interface.

The process:

The scheme below gives a graphic description of the entire process

With the Scripting introduced in ET GeoWizards 9.0 this process can be performed with just few lines of code. 

Note - If we remove the comments, the error checking (which repeats after each procedure), the declarations etc. -   the entire procedure is accomplished in 6 lines of code!

Sub SplitPolygonLayer()
  Dim pMxDoc As IMxDocument
  Dim pMap As IMap
  Dim pFeatureLayer As IFeatureLayer
  Dim pInFeatureClass As IFeatureClass
  Dim pOutFeatureClass As IFeatureClass
  Dim pTempFeatureClass As IFeatureClass
  Dim bDone As Boolean
  Set pMxDoc = ThisDocument
  Set pMap = pMxDoc.FocusMap
  Set pFeatureLayer = pMxDoc.SelectedLayer
  Set pInFeatureClass = pFeatureLayer.FeatureClass
  '=========================================
  Dim ET As New ETGW_Core
  Dim sOutFileName As String
  Dim dFuzzyTol As Double
  Dim pSplitLayer As IFeatureLayer
  Dim pSplitFeatureClass As IFeatureClass
  'an example on how to get a feature layer by name
  ' Get the polyline layer to be used for splitting
  Set pSplitLayer = ET.GetLayer("split_layer")
  If pSplitLayer Is Nothing Then
    Exit Sub
  End If
  Set pSplitFeatureClass = pSplitLayer.FeatureClass
  sOutFileName = "c:\00\split2.shp"
  'Convert the polygons to polylines
  Set pTempFeatureClass = ET.PolygonToPolyline(pInFeatureClass, "c:\00\pg2pl.shp")
  If pTempFeatureClass Is Nothing Then
    MsgBox "Error in step 0"
    Exit Sub
  End If
  'Merge the polylines with the Split polyline layer
  Set pTempFeatureClass = ET.merge(pTempFeatureClass, pSplitFeatureClass, "c:\00\merged.shp")
  If pTempFeatureClass Is Nothing Then
    MsgBox "Error in step 1"
    Exit Sub
  End If
  'Build polygons from merged dataset
  'Note that the bClean must be set to TRUE ==> the merged polylines should be cleaned before using them to build polygons
  dFuzzyTol = 0.002
  Set pOutFeatureClass = ET.BuildPolygons(pTempFeatureClass, "c:\00\pg_temp.shp", True, dFuzzyTol)
  If pOutFeatureClass Is Nothing Then
    MsgBox "Error in step 2"
    Exit Sub
  End If
  'In order to get the attributes from the original polygons we need to
  '1. Get the label points of the newly created polygons
  Set pTempFeatureClass = ET.PolygonToPoint(pOutFeatureClass, "c:\00\lab1.shp", _
  "Label", False)
  If pTempFeatureClass Is Nothing Then
    MsgBox "Error in step 3"
    Exit Sub
  End If
  '2. Attach the attributes from the original polygons to the label points
  Set pTempFeatureClass = ET.Spatial_Join(pTempFeatureClass, pInFeatureClass, _
  "c:\00\lab2.shp", "Within", False, 0)
  If pTempFeatureClass Is Nothing Then
    MsgBox "Error in step 4"
    Exit Sub
  End If
  '3. Attach the attributes from the label points to the split polygons
  Set pOutFeatureClass = ET.Spatial_Join(pOutFeatureClass, pTempFeatureClass, _
  sOutFileName, "Nearest", False, 0)
  If pOutFeatureClass Is Nothing Then
    MsgBox "Error in step 5"
    Exit Sub
  End If
  ' Delete the intermediate datasets
  bDone = ET.Deletefeature class("c:\00\pg2pl.shp")
  bDone = ET.Deletefeature class("c:\00\merged.shp")
  bDone = ET.Deletefeature class("c:\00\pg_temp.shp")
  bDone = ET.Deletefeature class("c:\00\lab1.shp")
  bDone = ET.Deletefeature class("c:\00\lab2.shp")
  '=========================================
  'Add the split polygons as a layer in the Map
  Set pFeatureLayer = New FeatureLayer
  Set pFeatureLayer.FeatureClass = pOutFeatureClass
  pFeatureLayer.Name = pOutFeatureClass.AliasName
  pMap.AddLayer pFeatureLayer
End Sub

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