Get shadow areas from a plane

I would like to get a set of areas (well, a set of vertices) corresponding of the shadow casted from some objects in my scene. They do not need to be perfect, it would be enough to have a bounding square or polygon. I am using Unity free, so I thought about 2 possible methods:

1) bake a lightmap selecting only the interested gameobjects, then extract the areas from the resulting lightmap

2) give my interested gameobjects a Projector component, set the preferred settings and then acquire the area casted on the plane at runtime

Which leads me to 2 questions:

• Which is the better way to achieve my purpose?

• In both methods, how can I access the set of vertices of the casted shadow projected on the plane?