A useful technique for estimating the shapes of many asteroids has been:

Question

Quizplus · Accepted Answer

Measurement of brightness variations caused by asteroid rotation is the most useful technique for estimating the shapes of many asteroids. As the asteroid rotates, its brightness varies in a predictable way, which can be used to build up a 3D shape model. This technique has been used extensively by astronomers, and has been validated by direct observations of some asteroids. Techniques such as occultations and spacecraft photography are also useful, but are more time-consuming and expensive to carry out.

A Useful Technique for Estimating the Shapes of Many Asteroids