How can I add a new field in a raster attribute table and loop through it?

Question

I am working with an existing raster attribute table. I wonder how can I add a new field to it and then loop through the existing records to populate this new field? Of course I have done this many times for a feature class and a database table but I do not know how to do it with a raster table. I work with VBA. Any code please? Thanks.

Answer 1

VBA sample code is here:

Public Sub CalculateArea(raster As IRaster, areaField As String)
    Dim bandCol As IRasterBandCollection
    Dim band As IRasterBand

    Set bandCol = raster
    Set band = bandCol.Item(0)

    Dim hasTable As Boolean
    band.hasTable hasTable
    If (hasTable = False) Then
        Exit Sub
    End If    

    If (AddVatField(raster, areaField, esriFieldTypeDouble, 38) = True) Then
        ' calculate cell size
        Dim rstProps As IRasterProps
        Set rstProps = raster

        Dim pnt As IPnt
        Set pnt = rstProps.MeanCellSize

        Dim cellSize As Double
        cellSize = (pnt.X + pnt.Y) / 2#

        ' get fields index
        Dim attTable As ITable
        Set attTable = band.AttributeTable

        Dim idxArea As Long, idxCount As Long
        idxArea = attTable.FindField(areaField)
        idxCount = attTable.FindField("COUNT")

        ' using update cursor
        Dim gridTableOp As IGridTableOp
        Set gridTableOp = New gridTableOp

        Dim cellCount As Long, cellArea As Double

        Dim updateCursor As ICursor, updateRow As IRow
        Set updateCursor = gridTableOp.Update(band.RasterDataset, Nothing, False)
        Set updateRow = updateCursor.NextRow()
        Do Until updateRow Is Nothing
            cellCount = CLng(updateRow.Value(idxCount))
            cellArea = cellCount * (cellSize * cellSize)

            updateRow.Value(idxArea) = cellArea
            updateCursor.updateRow updateRow

            Set updateRow = updateCursor.NextRow()
        Loop

    End If
End Sub

Private Function AddVatField(raster As IRaster, fieldName As String, fieldType As esriFieldType, fieldLength As Long) As Boolean
    Dim bandCol As IRasterBandCollection
    Dim band As IRasterBand

    Set bandCol = raster
    Set band = bandCol.Item(0)

    Dim hasTable As Boolean
    band.hasTable hasTable

    If (hasTable = True) Then
        Dim attTable As ITable
        Set attTable = band.AttributeTable

        If (attTable.FindField(fieldName)  -1) Then
            AddVatField = True
            Exit Function
        End If

        Dim newField As IField
        Dim fieldEdit As IFieldEdit

        Set newField = New Field
        Set fieldEdit = newField

        With fieldEdit
            .Name = fieldName
            .Type = fieldType
            .Editable = True
            .IsNullable = True
            .Length = fieldLength
        End With

        Dim gridTableOp As IGridTableOp
        Set gridTableOp = New gridTableOp
        gridTableOp.AddField band.RasterDataset, newField

        AddVatField = True
        Exit Function
    End If

    AddVatField = False
End Function

Answer 2

you could use IGridTableOp interface. reference: http://www.onspatial.com/2011/11/arcobjectsgrid-vatvalue-attribute-table.html

bool AddVatField(IRaster raster, string fieldName, esriFieldType fieldType, int fieldLength) {
    IRasterBandCollection bandCol = (IRasterBandCollection)raster;
    IRasterBand band = bandCol.Item(0);

    bool hasTable = false;
    band.HasTable(out hasTable);

    if (hasTable) {
        ITable attTable = band.AttributeTable;
        if (attTable.FindField(fieldName) != -1) {
            return true;
        }

        IField newField = new FieldClass();
        IFieldEdit fieldEdit = (IFieldEdit)newField;

        fieldEdit.Name_2 = fieldName;
        fieldEdit.Type_2 = fieldType;
        fieldEdit.Editable_2 = true;
        fieldEdit.IsNullable_2 = true;
        fieldEdit.Length_2 = fieldLength;

        IGridTableOp gridTableOp = new GridTableOpClass();
        gridTableOp.AddField(band.RasterDataset, newField);
        System.Runtime.InteropServices.Marshal.ReleaseComObject(gridTableOp);

        return true;
    }

    return false;
}

void CalculateArea(IRaster raster, string areaField) {
    IRasterBandCollection bandCol = (IRasterBandCollection)raster;
    IRasterBand band = bandCol.Item(0);

    bool hasTable = false;
    band.HasTable(out hasTable);
    if (!hasTable) return;

    // Add Field
    if (AddVatField(raster, areaField, esriFieldType.esriFieldTypeDouble, 38)) {
        // calculate cell size
        IRasterProps rstProps = (IRasterProps)raster;
        IPnt pnt = rstProps.MeanCellSize();
        double cellSize = (pnt.X + pnt.Y) / 2.0;

        // get fields index
        ITable attTable = band.AttributeTable;
        int idxArea = attTable.FindField(areaField);
        int idxCount = attTable.FindField("COUNT");

        // using update cursor
        IGridTableOp gridTableOp = new GridTableOpClass();
        ICursor updateCursor = gridTableOp.Update(band.RasterDataset, null, false);
        IRow updateRow = updateCursor.NextRow();
        while (updateRow != null) {
            int cellCount = Convert.ToInt32(updateRow.get_Value(idxCount));
            double cellArea = cellCount * (cellSize * cellSize);

            updateRow.set_Value(idxArea, cellArea);
            updateCursor.UpdateRow(updateRow);

            updateRow = updateCursor.NextRow();
        }
        System.Runtime.InteropServices.Marshal.ReleaseComObject(gridTableOp);
        System.Runtime.InteropServices.Marshal.ReleaseComObject(updateCursor);
    }
}