PolyObjectArea
Section: C Library Functions (3)
Updated: IRIT Version 6.0
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NAME
PolyObjectArea()
SYNOPSIS
geom_lib/geomvals.c:51
double PolyObjectArea(IPObjectStruct *PObj)
DESCRIPTION
Routine to evaluate the Area of the given geom. object, in object unit.
Algorithm (for each polygon): V3
1. Set Polygon Area to be zero. /\
Make a copy of the original polygon / \
and transform it to a XY parallel plane. / \V2
Find the minimum Y value of the polygon V4/ |
in the XY plane. \ |
2. Let V(0) be the first vertex, V(n) the last one. \ |
For i goes from 0 to n-1 add to Area the area \_______|
below edge V(i), V(i+1): V0 V1
PolygonArea += (V(i+1)x - V(i)x) * (V(i+1)y' - V(i)y') / 2
where V(i)y' is V(i)y - MinY, where MinY is polygon minimum Y value.
3. The result of step 2 is the area of the polygon itself.
However, it might be negative, so take the absolute result of step 2
and add it to the global ObjectArea.
Note step 2 is performed by another auxiliary routine: PolygonXYArea.
PARAMETERS:
PObj: A polyhedra object to compute its surface area.
FUNCTION RETURN VALUE
double: The area of object PObj.
ORIGIN
(C) Copyright 1989/90-95 Gershon Elber, Technion, IIT
Index
- NAME
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- SYNOPSIS
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- DESCRIPTION
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- PARAMETERS:
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- FUNCTION RETURN VALUE
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- ORIGIN
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