[GIS] Merging features into single programmatically

arcgis-desktoparcobjectsvba

I have a shapefile with polygons.
I can merge them manually by going into edit session and, selecting a some features to be merged, and then using merge button under Editor.

How to do this programmatically (in VBA)?

I've found the analogous ways but it doesn't solve the problem:

Standard Dissolve tool (from ArcToolbox) doesn't work correctly for this purpose, because it cuts off many fields and because it operates with whole FeatureClass but not with a separate features.
As I know by reading some examples, using an IBasicGeoprocessor (VBA) have the same problem – it operates with whole FeatureClass, producing a new FeatureClass, but not with separate features, mearging them within the same FeatureClass.

@kenbuja, Here is my try in vba (not in vb.net) :
Using a CType causes the Compile error: Sub or Function not defined.
What do I do wrong?

Dim pMxDoc As IMxDocument
Dim pCountyLayer As IFeatureSelection
Dim pCountySelection As ISelectionSet
Dim pCountyCursor As IFeatureCursor
Dim pCountyCursor2 As IFeatureCursor
Dim pFirstFeature As IFeature
Dim pSecondFeature As IFeature
Dim pThirdFeature As IFeature

Set pMxDoc = ThisDocument
Set pCountyLayer = pMxDoc.FocusMap.Layer(1)
Set pCountySelection = pCountyLayer.SelectionSet

' Create a cursors from the selected feature in Layer (1).
pCountySelection.Search Nothing, True, pCountyCursor
pCountySelection.Search Nothing, True, pCountyCursor2
' Return the selected features from the cursor.

Set pFirstFeature = pCountyCursor.NextFeature


Set pThirdFeature = pCountyCursor2.NextFeature
Set pSecondFeature = pCountyCursor2.NextFeature


Dim pFirstGeometry As IGeometry
Set pFirstGeometry = CType(pFirstFeature.Shape, IGeometry)
Dim pTopoOperator As ITopologicalOperator
Set pTopoOperator = CType(pFirstGeometry, ITopologicalOperator)
Dim pSecondGeom As IGeometry
Set pSecondGeom = CType(pSecondFeature.Shape, IGeometry)
Dim pMergedGeom As IGeometry
Set pMergedGeom = pTopoOperator.Union(pSecondGeom)

Best Answer

You can use the ITopologicalOperator's Union method to programmatically merge two polygons together. This example (written in VB.NET) shows how that's done.

Dim pFirstGeometry As IGeometry = CType(pFirstFeature.shape, IGeometry)
Dim pTopoOperator As ITopologicalOperator = CType(pFirstGeometry, ITopologicalOperator)
Dim pSecondGeom As IGeometry = CType(pSecondFeature.shape, IGeometry)
Dim pMergedGeom As IGeometry = pTopoOperator.Union(pSecondGeom)

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You might also try casting the Map to ISelectionEvents and calling SelectionChanged to notify of selection change.

[GIS] Merging separate features into single feature in shapefile programmatically

You can use the Geoprocessing tools programmatically. Here's an example (in VB.NET) from one of my applications (which uses many geoprocessing tools). The InputName can be a string or a feature class and it returns a feature class.

   Friend Function DissolveDataset(ByVal InputName As Object, ByVal DissolveField As String, ByVal StatsFields As String, ByVal OutputName As String) As ESRI.ArcGIS.Geodatabase.IFeatureClass

    Dim DissolveDS As New ESRI.ArcGIS.DataManagementTools.Dissolve
    Dim Result As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2

    Try
        Using releaser As New ESRI.ArcGIS.ADF.ComReleaser
            releaser.ManageLifetime(DissolveDS)
            DissolveDS.in_features = InputName
            DissolveDS.dissolve_field = DissolveField
            DissolveDS.statistics_fields = StatsFields
            DissolveDS.out_feature_class = OutputName

            Result = RunTool(DissolveDS, Nothing)
            If Result Is Nothing Then
                System.Windows.Forms.MessageBox.Show("Could not dissolve dataset")
                Return Nothing
            End If

            Return ReturnObjectfromResult(Result, "Feature Class")
        End Using

    Catch ex As Exception
        System.Windows.Forms.MessageBox.Show(ex.ToString, "Dissolve error")
        Return Nothing
    End Try

End Function

Friend Function RunTool(ByVal Process As ESRI.ArcGIS.Geoprocessor.IGPProcess, ByVal TC As ESRI.ArcGIS.esriSystem.ITrackCancel2, Optional ByVal AddOutput As Boolean = False) As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2

    Dim Result As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2

    Try
        System.Windows.Forms.Cursor.Current = Windows.Forms.Cursors.WaitCursor
        Dim GP As New ESRI.ArcGIS.Geoprocessor.Geoprocessor

        GP.AddOutputsToMap = AddOutput

        Result = CType(GP.Execute(Process, Nothing), ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2)
        If Result.Status <> ESRI.ArcGIS.esriSystem.esriJobStatus.esriJobSucceeded Then ReturnMessages(Result, "Geoprocessing Error")
        GP.ClearMessages()
    Catch ex As Exception
        ReturnMessages(Result, "Fail")
        System.Windows.Forms.MessageBox.Show(ex.ToString, "Run Geoprocessor")
    End Try

    Return Result

End Function

Private Sub ReturnMessages(ByVal pResult As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2, ByVal Title As String)

    Dim ErrorMessage As String

    If pResult Is Nothing Then Exit Sub

    If pResult.MessageCount > 0 Then
        For Count As Integer = 0 To pResult.MessageCount - 1
            ErrorMessage += pResult.GetMessage(Count)
        Next
    End If


    System.Windows.Forms.MessageBox.Show(ErrorMessage, Title)

End Sub

Friend Function ReturnObjectfromResult(ByVal result As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2, ByVal Type As String) As Object

    Dim GPVal As ESRI.ArcGIS.Geodatabase.IGPValue
    Dim InMemFC As String
    Dim GPUtil As ESRI.ArcGIS.Geoprocessing.IGPUtilities3 = New ESRI.ArcGIS.Geoprocessing.GPUtilities

    Try
        GPVal = result.GetOutput(0)
        InMemFC = GPVal.GetAsText()

        Select Case Type
            Case "Feature Class"
                Return GPUtil.OpenFeatureClassFromString(InMemFC)
            Case "Table"
                Return GPUtil.OpenTableFromString(InMemFC)
            Case "Feature Layer"
                Return GPUtil.OpenFeatureLayerFromString(InMemFC)
            Case Else
                Return Nothing
        End Select

    Catch ex As Exception
        System.Windows.Forms.MessageBox.Show(ex.ToString, "ReturnObjectfromResult error")
        Return Nothing
    End Try

End Function

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