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Calculating Static Extents

Some providers require that you perform a SelectAggregates on a dataset to determine its extents, specifiying the SpatialExtents function as one of the properties to calculate.

C++ Example

  FdoPtr<FdoISelectAggregates> agg = (FdoISelectAggregates*)con->CreateCommand(FdoCommandType_SelectAggregates);
  agg->SetFeatureClassName(L"MyFeatureClass");
  FdoPtr<FdoIdentifierCollection> props = agg->GetPropertyNames();

  FdoPtr<FdoExpression> exp = FdoExpression::Parse(L"SpatialExtents(GEOMETRY)");
  FdoPtr<FdoComputedIdentifier> se = FdoComputedIdentifier::Create(L"Extents", exp);
  props->Add(se);

  FdoPtr<FdoIDataReader> extrdr = agg->Execute();
  extrdr->ReadNext();

  FdoPtr<FdoByteArray> ba = extrdr->GetGeometry(L"Extents");
  //ba contains the extents polygon, in FGF array form, use FdoIGeometry APIs to get the numbers out of it.

C# Example

    public IPolygon GetExtents()
        {
            IPolygon retpolygon;
            ISelectAggregates pselagree = (ISelectAggregates)FDOConnection.CreateCommand(CommandType.CommandType_SelectAggregates);
            pselagree.SetFeatureClassName(System.IO.Path.GetFileNameWithoutExtension(OpenedFile)); // Path and name of the shape file....
            
            IdentifierCollection props = pselagree.PropertyNames;
            Expression exp = Expression.Parse("SpatialExtents(Geometry)");
            ComputedIdentifier se = new ComputedIdentifier("Extents", exp);

            props.Add(se);

            IDataReader FDOReader = pselagree.Execute();
            FgfGeometryFactory GeoFac = new FgfGeometryFactory();

            FDOReader.ReadNext();
            Byte[] Tmppts = FDOReader.GetGeometry("Extents");

            IGeometry Geo = GeoFac.CreateGeometryFromFgf(Tmppts);

            retpolygon = (IPolygon)Geo;

            return retpolygon;

        }

Contributors

• Traian Stanev
• Shaik Esu