~F81. VECTOR & 2. ARC NODE FORMAT.

	_____________________________________________ 
	word |        CW         |        CCW        |
	  0  |              vector ring              | 3
	_____|___________________|___________________|
	word |        DAD        |        SON        |
	  1  |      polygon      |    arc or vector  | 3
	_____|___________________|___________________|
	word |       type        |       reloc       |
	  2  |                   |      33 0003      |
	_____|___________________|___________________|
	word |        row        |        col        |
	  3  |      0000.00      |      0000.00      | 0
	_____|___________________|___________________|
	word |       cntrst      |       ncnt        |
	  4  |                   |      length       | 0
	_____|___________________|___________________|
	word |                                       |
	  5  |                zdepth                 | 0
	_____|_______________________________________|
	word |                   |                   |
	  6  |       NTIME   time line   PTIME       | 3
	_____|___________________|___________________|

	The format of vectors  and arcs is identical. Inside  CRE the
term "vector"  has the connotation of being  strictly a horizontal or
vertical generated  by  the contouring  step;  whereas  an arc  is  a
vector  generated   by  the  smoothing  step.   Vectors  contain  the
fundamental  geometric datum of an  image locus.   The image locus is
stored in the halfword datums  named row and col,  which  contain the
row and column  of a point in units 1/64 of a  pixel. (A "pixel" is a
"picture element").  Vectors and  arcs also  contain the  photometric
datum of edge contrast.

	Vectors always  belong to a  polygon node,  a pointer to  the
polygon  of each vector is  stored in the link  named DAD; as members
of a polygon the vectors form a loop which is always connected  so that
each vertex  has a  neighboring vertex  in the  clockwise and  in the
counter  clockwise  directions about  the polygon's  perimeter; these
perimeter pointers  are stored  in the  link positions  named CW  and
CCW. Vectors never cross, arcs cross on occassions but can be fixed.

	The ncnt datum of arcs and vectors    contains  their length.
The  time line links, NTIME and PTIME,  may point  to a corresponding
arc or  vector in the  image previous  or subsequent  to the  current
image.  (The  zdepth  datum  contains a  positive  number  indicating
distance  from the  camera's image  plane; the zdepth  computation is
not properly implemented as of May 1973).
~I1973,800;F8- 13 -