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sn#046239 filedate 1973-06-05 generic text, type T, neo UTF8
~F8DATA STRUCTURE: KINDS OF NODES.
The are eight kinds of CRE nodes: Vector, Arc, Polygon,
Shape, Image, Level, Film and Empty.
1. At the very top of all the structure is the film node, the film
node is unique and serves as an OBLIST from which all other nodes
may be reached. The film node embodies the idea of a piece of
celluloid film or a length of magnetic video tape. A film is a
sequence of images taken by the same camera of the same scene with
only a small amount of action between images.
2. An image node represents the familiar two dimensional idea of a
photograph or an oil painting or to be exact a digital video image
of 216 rows by 288 columns of numbers ranging from 0 for dark to 63
for bright. The image is formed by a thin lens and is projected on
a flat image plane. The idea of an image is so common that it is
easy to overlook the wonder of sun light scattering off of surfaces,
refracting thru a lens, and forming a complex pattern called a real
image.
3. Below the image node are the intensity contour levels. A contour
level is a binary image that results from thresholding a gray scaled
image. So an image is composed of levels, and in turn, a level is
composed of polygons.
4. A Polygon node represents the idea of a contour loop which
always closes upon itself and does not cross itself or any other
contour. Contour loops are approximated by a ring of vectors; hence,
the term "polygon". The contour polygons always have at least three
sides and are simply connected.
5. Shape nodes contain data about one or two polygons. The data in a
shape node is not a positive representation of the notion of shape;
but is rather the parameters of allignment and normalization that
must be compensated before shapes can be compared.
6. Vector nodes contain the locus of an image vertex; however since
vectors always belong to a polygon and always have two neighbors;
their counterclockwise neighbor is considered to determine their
vector direction.
7. Arc nodes are vectors that are made by the polygon smoothing
routine; one arc typically replace several vectors. When both arcs
and vectors are being discussed; vectors are strictly horizontal and
vertical, whereas arcs may point in any direction.
8. Empty nodes are an artifact of the fixed node size dynamic
storage allocation mechanism used in CRE. Entities are made by
taking empty nodes from an AVAIL list and entities are killed by
returning their node to the AVAIL list; there is no garbage
collector, but there is a space compactor.
~I1973,800;F8- 7 -