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sn#046269 filedate 1973-06-06 generic text, type T, neo UTF8
~F85. COMPARING.
The compare step of CRE, CMPARE, connects the polygons and
arcs of the current image with corresponding polygons and arcs of
the previous image. CMPARE solves the problem of correlating
features between two similar images and is composed four sub
sections:
1. make shape nodes for polygons.
2. compare and connect polygons one to one.
3. compare and connect polygons two to one.
4. compare and connect vertices of connected polygons.
First, the shape nodes of all the polygons of an image are
computed. The shape node contains the center of mass and the lamina
inertia tensor of a polygon. The lamina inertia tensor of a polygon
with N sides is computed by summation over N trapezoids. The
trapezoid corresponding to each side is formed by dropping
perpendiculars "up" to the top of the image frame; each such
trapezoid consists of a rectangle an a right triangle; since the
sides of polygons are directed vectors the areas of the triangles
and rectangles can be arranged to take positive and negative values
such that a summation will describe the interior region of the
polygon as positive. The equations necessary for computing the
lamina inertia tensor of a polygon are collected in a table in the
postscripts to this paper and were derived by using Goldstein's
Classical Mechanics [1] as a reference. The meaning of the inertia
tensor is that it characterizes each polygon by a rectangle of a
certain length and width at a particular location and oriention; and
of further importance such inertia tensors can be "added" to
characterize two or more polygons by a single rectangle. It is the
lamina inertia tensor rectangles that are actually compared by CRE.
Second, all the shapes of the polygons of one level of the
first image are compared with all the shapes of the polygons of the
corresponding level of the second image for nearly exact match. The
potentially (M*N/2) compares is avoided by sorting on the center of
mass locations. In CRE, which is intended for comparing sequences
of pictures of natural scenes; match for center of mass location is
tested first and most strictly, followed by match for inertia.
Pointers between matching polygons are placed in the time link
positions of the polygon nodes and the polygons are considered to be
mated in time. ~I1973,800;F8- 32 -