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PIXWT

PIXWT

Name


PIXWT

Purpose


Circle-rectangle overlap area computation.

Description


Compute the fraction of a unit pixel that is interior to a circle.
The circle has a radius r and is centered at (xc, yc). The center of
the unit pixel (length of sides = 1) is at (x, y).

Category


CCD data processing

Calling Sequence


area = Pixwt( xc, yc, r, x, y )

Inputs


xc, yc : Center of the circle, numeric scalars
r : Radius of the circle, numeric scalars
x, y : Center of the unit pixel, numeric scalar or vector

Optional Input Parameters


None.

Keyword Parameters


None.

Outputs


Function value: Computed overlap area.

Example


      What is the area of overlap of a circle with radius 3.44 units centered
      on the point 3.23, 4.22 with the pixel centered at [5,7]
      IDL> print,pixwt(3.23,4.22,3.44,5,7) ==> 0.6502

Common Blocks


    None.

Procedure


Divides the circle and rectangle into a series of sectors and
triangles. Determines which of nine possible cases for the
overlap applies and sums the areas of the corresponding sectors
and triangles. Called by aper.pro

Notes


      If improved speed is needed then a C version of this routines, with
      notes on how to linkimage it to IDL is available at
      ftp://ftp.lowell.edu/pub/buie/idl/custom/

Modification History


    Ported by Doug Loucks, Lowell Observatory, 1992 Sep, from the
    routine pixwt.c, by Marc Buie.



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