The description of an obstacle always start by the function
p3d_beg_desc(P3D_OBSTACLE, obst_name). This time, p3d_beg_desc
checks if the description of an environment has been started, if we
are not describing a robot or another obtsacle at the same time and
calls the function void *p3d_beg_obj(char *name, int type)
with the name obst_name and the type P3D_OBSTACLE as inputs.
The function p3d_beg_obj allocates an object structure
p3d_obj (cf Annex ) of name obst_name, and
of type P3D_OBSTACLE, intializes it, stores it as the current
object of the environment and returns it as an output.
Once the obstacle has been initialized, the user can add one or several
polyhedrons to describe its geometry (cf Fig. ). Those
polyhedrons can be created using regular geometric primitives or can
be described vertex by vertex.