Name

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    cgetrng

Purpose (one Line)

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    How to integrate over a circle.

Description

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    This procedure is called to determine how to iterate when integrating
  over a circle. The circle's center is at (xc,yc), and its radius is r.
  For pixels with x-coordinate x, those in the intervals [y0,y1) and [y2,y3)
  are on or near the circle. Those in the interval [y1,y2) are definitely
  inside; all others are definitely outside.
    Of course, the routine can be called to determine an interval for fixed
  y by calling it as cgetrng,yc,xc,r,y,x0,x1,x2,x3.
    The appropriate way to integrate over a circle is therefore as follows:
  cgetrng,xc,yc,r,Round(xc),y0,y1,y2,y3
  for (y = y0; y <= y3-1; y=y+1) {
    cgetrng, yc, xc, r, y, x0, x1, x2, x3;
    for (x = x0; x <= x1-1; x=x+1) sum = sum + value(x,y)*pixwt(xc,yc,r,x,y);
    for (x = x1; x <= x2-1; x=x+1) sum = sum + value(x,y);
    for (x = x2; x <= x3-1; x=x+1) sum = sum + value(x,y)*pixwt(xc,yc,r,x,y);
    }

Category

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    CCD data processing

Calling Sequence

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    cgetrng, xc, yc, r, x, y0, y1, y2, y3

Inputs

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    xc, yc : Center of the circle.
    r : Radius of the circle.
    x : X coordinate for the intervals to be determined.

Optional Input Parameters

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    None.

Keyword Parameters

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    None.

Outputs

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    y0, y1, y2, y3 : The endpoints of the three intervals of interest.

Common Blocks

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    None.

Side Effects

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Restrictions

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    None.

Procedure

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    Determine three intervals along the x input coordinate: The
    intervals [y0,y1), [y1,y2), and [y2,y3).

Modification History

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    Ported by Doug Loucks, Lowell Observatory, 1992 Sep, from the
    routine cgetrng in pixwt.c, by Marc Buie.
    4/1/93, DWL, Added argument validation (badpar).