Converting 2D elements for use in 3D. Any 3D element(s) can be saved as an object with the Save Project As... menu command. (In Archicad 11, Save 3D Model As...) This technique is known as 'slabifying' since such models are often built from slabs. Objects saved in this way are dumb (not parametric), but it's still a useful trick. 2D
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In creative GDL, windows are about the most complex things there are. Yet to slabify a window is no harder than a regular object. This example is for an silly piece of glazing, but you could use the same technique for a custom trim panel 'window'.