Take a look at the `DirectionCalculation` Revit SDK sample and The Building Coder discussion of it
on south facing walls:
http://thebuildingcoder.typepad.com/blog/2010/01/south-facing-walls.html
That will provide a good starting point for you.
It uses the built-in wall function parameter `FUNCTION_PARAM` to filter for exterior walls.
I updated the code presented there and added it to The Building Coder samples for you, in the CmdCollectorPerformance.cs module lines L293-L323:
https://github.com/jeremytammik/the_building_coder_samples
https://github.com/jeremytammik/the_building_coder_samples/blob/master/BuildingCoder/BuildingCoder/CmdCollectorPerformance.cs#L293-L323
First, we implement a predicate method `IsExterior` that checks this parameter value to determine whether a wall type is exterior or not:
/// <summary>
/// Wall type predicate for exterior wall function
/// </summary>
bool IsExterior( WallType wallType )
{
Parameter p = wallType.get_Parameter(
BuiltInParameter.FUNCTION_PARAM );
Debug.Assert( null != p, "expected wall type "
+ "to have wall function parameter" );
WallFunction f = (WallFunction) p.AsInteger();
return WallFunction.Exterior == f;
}
With that, you can retrieve all exterior walls with a filtered element collector like this:
/// <summary>
/// Return all exterior walls
/// </summary>
IEnumerable<Element> GetAllExteriorWalls(
Document doc )
{
return new FilteredElementCollector( doc )
.OfClass( typeof( Wall ) )
.Cast<Wall>()
.Where<Wall>( w =>
IsExterior( w.WallType ) );
}
Since the wall function filter is just checking a parameter value, the performance of this filtering process could be significantly enhanced by using a parameter filter instead of the slow .NET based `IsExterior` method post-processing:
http://thebuildingcoder.typepad.com/blog/2010/06/parameter-filter.html
Cheers,
Jeremy
