Question-and-Answer Resource for the Building Energy Modeling Community
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The OpenStudio gbxml forward translator at least writes both.
RectangularGeometry defines a kind of an area-equivalent bounding surface: this represents the overall geometry of the surface, by defining an equivalent rectangular surface with the same area, a starting point, and a tilt, PlanarGeometry element has a PolyLoop element with all points / vertices describing the surface as it is actually in 3D space.https://github.com/NREL/OpenStudio/blob/d06c9047fd348e7edf52090486279f210fe947f9/src/gbxml/ForwardTranslator.cpp#L891-L978
Couple of other sources that discuss this:
