functions in pl3d.i - g

             get3_centroid(xyz, nxyz)  
          or get3_centroid(xyz)  
 
     return 3D centroids for polygons with vertices XYZ.  If NXYZ is  
     specified, XYZ should be 3-by-sum(nxyz), with NXYZ being the  
     list of numbers of vertices for each polygon (as for the plfp  
     function).  If NXYZ is not specified, XYZ should be a quadrilateral  
     mesh, 3-by-ni-by-nj (as for the plf function).  In the first case,  
     the return value is 3-by-numberof(NXYZ); in the second case, the  
     return value is 3-by-(ni-1)-by-(nj-1).  
     The centroids are constructed as the mean value of all vertices  
     of each polygon.  
interpreted function, defined at i/pl3d.i   line 480  

             get3_light(xyz, nxyz)  
          or get3_light(xyz)  
 
     return 3D lighting for polygons with vertices XYZ.  If NXYZ is  
     specified, XYZ should be 3-by-sum(nxyz), with NXYZ being the  
     list of numbers of vertices for each polygon (as for the plfp  
     function).  If NXYZ is not specified, XYZ should be a quadrilateral  
     mesh, 3-by-ni-by-nj (as for the plf function).  In the first case,  
     the return value is numberof(NXYZ); in the second case, the  
     return value is (ni-1)-by-(nj-1).  
     The parameters of the lighting calculation are set by the  
     light3 function.  
interpreted function, defined at i/pl3d.i   line 363  

             get3_normal(xyz, nxyz)  
          or get3_normal(xyz)  
 
     return 3D normals for polygons with vertices XYZ.  If NXYZ is  
     specified, XYZ should be 3-by-sum(nxyz), with NXYZ being the  
     list of numbers of vertices for each polygon (as for the plfp  
     function).  If NXYZ is not specified, XYZ should be a quadrilateral  
     mesh, 3-by-ni-by-nj (as for the plf function).  In the first case,  
     the return value is 3-by-numberof(NXYZ); in the second case, the  
     return value is 3-by-(ni-1)-by-(nj-1).  
     The normals are constructed from the cross product of the lines  
     joining the midpoints of two edges which as nearly quarter the  
     polygon as possible (the medians for a quadrilateral).  No check  
     is made that these not be parallel; the returned "normal" is  
     [0,0,0] in that case.  Also, if the polygon vertices are not  
     coplanar, the "normal" has no precisely definable meaning.  
interpreted function, defined at i/pl3d.i   line 421  

             get3_xy, xyz, x, y  
          or get3_xy, xyz, x, y, z, 1  
 
     Given 3-by-anything coordinates XYZ, return X and Y in viewer's  
     coordinate system (set by rot3, mov3, orient3, etc.).  If the  
     fifth argument is present and non-zero, also return Z (for use  
     in sort3d or get3_light, for example).  If the camera position  
     has been set to a finite distance with setz3, the returned  
     coordinates will be tangents of angles for a perspective  
     drawing (and Z will be scaled by 1/zc).  
interpreted function, defined at i/pl3d.i   line 520  

             gnomon  
          or gnomon, onoff  
 
     Toggle the gnomon display.  If ONOFF is non-nil and non-zero,  
     turn on the gnomon.  If ONOFF is zero, turn off the gnomon.  
     The gnomon shows the X, Y, and Z axis directions in the  
     object coordinate system.  The directions are labeled.  
     The gnomon is always infinitely far behind the object  
     (away from the camera).  
     There is a mirror-through-the-screen-plane ambiguity in the  
     display which is resolved in two ways: (1) The (X,Y,Z)  
     coordinate system is right-handed, and (2) If the tip of an  
     axis projects into the screen, it's label is drawn in opposite  
     polarity to the other text on the screen.  
interpreted function, defined at i/pl3d.i   line 734