Billboarding/impostors mean, roughly, representing complex 3D objects in 2D or with simple quadrilaterals, for the sake of LOD systems.
Consider the case of rendering a very numerous asteroid field where one base asteroid mesh is instanced X times. If none of the instances of the mesh are re-scaled, it is easy to replace them with a billboard/impostor: one should just generate a billboard or impostor for the base asteroid mesh and substitute each asteroid instance with an instance of the billboard/impostor when desired.
Now, if each instance of the asteroid mesh that is present in the asteroid field is supposed to be re-scaled (e.g. to give the illusion of diversity to an asteroid field), this becomes much more complicated. Re-scaling a billboard quad of the base asteroid mesh, for instance, would not mimic the re-scaled instances of the asteroid mesh. At the same time, it is not clear whether using techniques like true-impostor would solve that any further.
Thus, my question is: is there any impostoring technique that would allow that? I.e. pre-generating an impostor of the base asteroid mesh, then scaling each impostor's instance in a way that would mimic the re-scaling of the instances of the asteroid mesh?
I have been reading the recent literature on advanced billboarding/impostor techniques (true impostors, 3-view impostors, volumetric impostors, etc), but I am still confused about that.