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Re: Center of ARC in Cartesian coordinates !!!
Posted:
Feb 2, 1998 10:41 AM


> I am held up with a problem in playing with ARCS. I need to create ARC > using a primitive which needs > (i) arc center point and start and end points of the arc. > > But I am falling short of one inputs and that is the center point. > I do have another input and that is the radius of the ARC.
Mahesh,
If I understand your question you are trying to develop a procedure ARC_3pt(startx,starty,midx,midy,endx,endy) and what you have to work with are the two points (startx,starty), (endx,endy) and radius.
If this is your problem then you need to come up with an additional input because these five inputs do not uniquely determine an arc. Here is an easy counterexample:
Suppose the starting point is (1, 0) the ending point is (0, 1) and the radius is 1. One solution is the unit circle centered at the origin which would output the midpoint of the arc (midx, midy) = (1/sqrt(2), 1/sqrt(2)). But a second solution is the unit circle centered at (1, 1). The two endpoints still determine a quarter circle but now the arc's midpoint is (11/sqrt(2), 11/sqrt(2)).
Alan
 Alan Lipp Williston Northampton School Easthampton, MA 01027 4135271520



