The desciption of a scene always starts by function
p3d_beg_desc(P3D_ENV,env_name), that calls the function void
*p3d_beg_env(char* name) with the name env_name as input. The
function p3d_beg_env allocates an environment structure
p3d_env (cf Annex ) of name env,
intializes it and returns it as an output.
When all the robots and obstacles have been described, the function p3d_end_desc() is called, that calls the function int p3d_end_env(void) . This function checks if some obstacles and at least one robot have been described in the environment, and finishes the initialization of the environnement.
Between the command p3d_beg_desc P3D_ENV env and the corresponding command p3d_end_desc, somes obstacles and at least one robot must be described.