NAME: pixwt PURPOSE: (one line) 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: Pixwt( xc, yc, r, x, y ) INPUTS: xc, yc : Center of the circle. r : Radius of the circle. x, y : Center of the unit pixel. OPTIONAL INPUT PARAMETERS: None. KEYWORD PARAMETERS: None. OUTPUTS: Function value: Computed overlap area. COMMON BLOCKS: None. SIDE EFFECTS: RESTRICTIONS: 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. MODIFICATION HISTORY: Ported by Doug Loucks, Lowell Observatory, 1992 Sep, from the routine pixwt.c, by Marc Buie.