Autodesk Developer Network 2011
Autodesk
Geometry API
§HostObjectUtils - locate the faces of a given roof, floor or wall (host objects)
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§ExtrusionAnalyzer - Allow fitting a geometry into the shape of an extrusion
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§Geometry Filters - find elements that intersect the solid geometry of element
§ElementIntersectsElementFilter
§ElementIntersectsSolidFilter
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Geometry API now provides shortcuts to locate the face of a given roof, floor or wall – basically host objects, using HostObjectUtils.

We can also fit a given geometry into the shape of an extrusion using the ExtrusionAnalyzer class.

Revit 2012 API has new geometry filters which help find elements whose actual 3D geometry intersects the 3D geometry of target object. With ElementIntersectsElementFilter, the target object is another element.
With ElementIntersectsSolidFilter, the target object is any solid, including one created from scratch using GeometryCreationUtilities. Both these filters are slow filters.