WPF: Combine Geometries / Canvas for Geometries?

I have 2 geometries A and B which I'd like to combine like shown at the end of the following drawing: http://www.imagebanana.com/view/9vm6zoy/geocombine.png

How could one do this? Is开发者_StackOverflow中文版 there something like a "virtual canvas for geometries" where I can place A and B, move B accordingly and then get a geometrie from this? Thanks for any hint!

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For the records: GeometryGroup should do it.