On Mon, 31 Jan 2005 08:34:46 -0800, aiiadict wrote: > I don't know the geometry term, but > I want to compute which cells > in a graph are covered by a "pie slice" > of a circle. In the subject line you also mention the area of the circle. I'll give you a couple of formulae. One is more interesting than the other. Area = Pi * r^2 Pi is a constant. It is an infinite non-repeating real number. Depending on the level of accuracy you want you would use different approximations. Here is a formula which gives a better approximation than is in most calculators. Pi = 355 / 113 An engineer friend told me the best way to remember it is doubling the first three odd numbers (113355) and dividing the second three by the first. If you want to figure out the area of a pie slice, you can determine the length of the arc and compare it to the circumference of the circle. Then look at what percentage of the entire circumference is occupied by the arc. Multiply the percentage by the volume of the circle and voila... You have the area of the pie slice. I wish they gave us interesting problems like this when I took comp. sci.. Later Mike