Stereometry is a way of learning how to draw the human figure by breaking it down into geometric shapes and basic generic measurements. The stereometric approach to drawing people was popularized during the Renaissance by artists like Leonardo da Vinci, Albrecht Dürer, etc.
I've spent so much time the last few years on still lifes, color studies, and landscapes that my anatomy knowledge has atrophied a bit, so I'm going back over some of the basics. I'm going through the Basic Human Anatomy by Roberto Osti to help me with this, and what I like about his approach is that he encourages artists to actually understand how muscles and bones work in the human body (instead of just copying them visually like how most artists do....)
I agree with Osti, in that the only way an artist can advance enough to draw people from imagination is to learn and understand how the human figure moves instead of just copying it.
To draw people from memory instead of relying on photographs or models, one needs to study where muscles are located, how they're connected in different spots, how certain movements cause certain muscles to stretch or bend, etc. The more an artist studies and internalizes this information, the more permanent the knowledge will become and eventually it'll become second nature.
Without this knowledge, an artist will always be heavily dependent on photographs and models just to even begin the composition of a drawing of a person or character- and this kind of dependence on references leads to artwork that is limited itself, and is thus often boring.
