geom:section

(geom:section solid &key normal offset origin)

The cross-section loops where a plane cuts the solid -- a cross-section drawing in one call. The plane is :normal (an axis keyword like :z, the default, or a vector) plus either :offset (the signed distance from the origin along the normal, default 0.0) or :origin (a point on the plane). Each loop is a rank-2 (n 3) packed float32 array of world points, outer boundaries wound counter-clockwise seen from the normal's positive side and holes clockwise; a plane that misses the solid answers nil. A section of a torus at its equator is two loops -- the boundary and the hole. See the solid modeling guide.