How to use IRelationalOperator2 and GeometryBag

Question

I want to use the IsNear method of IRelationalOperator2. The documentation says that GeometryBag supports the IRelationalOperator2 interface. But this just doesn't work and results in an exception "... unable to cast COM object ... No such interface supported..."

IRelationalOperator2 relationalOperator = (IRelationalOperator2)geometry;

The same code works fine with IRelationalOperator but there is no IsNear method:

IRelationalOperator relationalOperator = (IRelationalOperator)geometry;

What is wrong - the code, the documentation or is it a bug? "geometry" is a geometry of geometry type esriGeometryBag and contains some polylines. I used the straight cast to get the .NET exception.

Answer 1

There's definitely something fishy going on here with 10.0 sp2.

I can cast a geometry bag to IRelationalOperator2, otherwise this test would say "unable to cast", plus I'd get a null reference exception.

However, on the first call to IsNear I get the exception.

System.InvalidCastException occurred
  Message=Unable to cast COM object of type 'ESRI.ArcGIS.Geometry.GeometryBagClass' to interface type 'ESRI.ArcGIS.Geometry.IRelationalOperator2'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{839F5C7E-ED5F-4B3F-8F97-C0A9CC4817EE}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
  Source=ESRI.ArcGIS.Geometry

Here's the test:

private void GBTest(IPoint pnt)
{
    // this line does not fail
    var relop = new GeometryBagClass() as IRelationalOperator2;

    if (relop == null)
        Debug.Print("unable to cast"); // this doesn't print out

    var coll = relop as IGeometryCollection;
    coll.AddGeometry(pnt);
    //((ISpatialIndex)coll).AllowIndexing = true;
    //((ISpatialIndex)coll).Invalidate();

    var pnt2 = ((IClone)pnt).Clone() as IPoint;
    ((ITransform2D)pnt2).Move(100.0, 100.0);
    if (relop.IsNear(pnt2, 1000.0)) // exception here
        Debug.Print("test 1 fail");

    if (!relop.IsNear(pnt2, 10.0))
        Debug.Print("test 2 fail");
}

Here's another test. Notice how I can cast without an exception, but get an InvalidCast exception when calling IsNear.

private void GBTest(IPoint pnt)
{
    var coll = new GeometryBagClass();
    ((IGeometry)coll).SpatialReference = pnt.SpatialReference;

    coll.AddGeometry(pnt);
    coll.GeometriesChanged();

    var relop = (IRelationalOperator2)coll; // would expect the exception here

    var pnt2 = ((IClone)pnt).Clone() as IPoint;
    ((ITransform2D)pnt2).Move(100.0, 100.0);
    if (relop.IsNear(pnt2, 1000.0)) // exception here
        Debug.Print("test 1 fail");

    if (!relop.IsNear(pnt2, 10.0))
        Debug.Print("test 2 fail");
}

Answer 2

I would guess that it is a bug with the documentation since a GeometryBag is a collection of points/lines/polygons. Doing some ITopologicalOperator operations on a mixed and matched collection of geometry types could be impossible. If you used an IGeometryCollection of polylines though I think your solution would work.