~F84. SHAPE NODE FORMAT.

	_____________________________________________ 
	word |        CW         |        CCW        |
	  0  |          fusion shape ring            | 3
	_____|___________________|___________________|
	word |       perm        |       area        |
	  1  |                   |                   | 0
	_____|___________________|___________________|
	word |       type        |       reloc       |
	  2  |        10         |      30 0030      |
	_____|___________________|___________________|
	word |        row        |        col        |
	  3  |      0000.00      |      0000.00      | 0
	_____|___________________|___________________|
	word |        pxy        |        mzz        |
	  4  |product of inertia |   Z-axis moment   | 0
	_____|___________________|___________________|
	word |       NGON        |       PGON        |
	  5  |   fusion polygon  |    main polygon   | 3
	_____|___________________|___________________|
	word |        mxx        |        myy        |
	  6  |   X-axis moment   |   Y-axis moment   | 0
	_____|___________________|___________________|


	The shape  node contains the  data necessary  for normalizing
two  polygons so that  only their  shapes remain. In  particular, the
row and col of  a shape node  is the center of  mass of the  polygon;
area is  the area;  perm is  the length of  perimeter; and  mxx, myy,
mzz,  pxy is  the polygons inertia  tensor (from  which the principle
angle of  orientation can be  computed). When  given two shapes,  the
centers of mass may be  alligned; the principle angles may be allign;
and the areas (or permeter) of the two may be normalized.

	There are  two  kinds of  shapes: polygon  shapes and  fusion
shapes. Polygon  shapes correspond to a single  polygon pointed at by
the PGON link.  The CW,  CCW and NGON  links of a  polygon shape  are
NIL. Fusion  shapes are  temporary nodes  belonging to  a level  as a
ring  thru CW and CCW.  Fusion shapes correspond  to the summation of
two unmated  polygons  which are  pointed  to by  the NGON  and  PGON
links. The expressions relating to  the inertia tensor  and to fusion
summation are given in the section on polygon comparing.

	The datums named perm,  area, pxy,  mxx, myy, mzz contain the
left  half of a PDP-10  floating number.  (Technical  note: half of a
floating number has  9 bits of  precision and  should be expanded  to
full word by  using the (mirabile dictu !) HLLE  instruction in order
to  avoid an illegal floating zero  caused by truncating numbers like
-1023.0; in CRE, only the product of inertia will ever be negative).
~I1973,800;F8- 15 -