~F85. LEVEL NODE FORMAT.

	_____________________________________________ 
	word |        CW         |        CCW        |
	  0  |              level ring               | 3
	_____|___________________|___________________|
	word |        DAD        |        SON        |
	  1  |       image       |     1st polygon   | 3
	_____|___________________|___________________|
	word |       type        |       reloc       |
	  2  |                   |      33 0200      |
	_____|___________________|___________________|
	word |                   |                   |
	  3  |       ---         |       ---         | 0
	_____|___________________|___________________|
	word |       ALT         |       ncnt        |
	  4  | (1st fusion shape)|threshold cut level| 2
	_____|___________________|___________________|
	word |                   |                   |
	  5  |       ---         |       ---         | 0
	_____|___________________|___________________|
	word |                   |                   |
	  6  |       ---         |       ---         | 0
	_____|___________________|___________________|

	Every level belongs to  an image pointed to by  the DAD link;
the  ring of levels of  an image is  formed in the CW  and CCW links;
the son of  a level is its  first polygon and  that first polygon  is
the upper left most polygon of the level.

	The ncnt datum  of a level contains its  threshold cut value,
which  is an  integer  between -1  and 63.   The  -1 level  is always
generated, and it contains a single polygon with four  sides.  The -1
level's polygon is called  the border polygon; the fiction being that
every point  beyond  the  edges  of  the  televsion  picture  has  an
intensity value of -2, which is blacker than black.

	The ALT link of a level contains  a temporary pointer to that
level's ring of fusion shapes during polygon compare time mating.
~I1973,800;F8- 16 -