In article <opr2k5x2xmp4ukzs@news.povray.org>,
 Phil Cook <phi### [at] nospamdeckingdealscouk> wrote:

> I'm trying to create a crescent moon shape as per the code below, which 
> took a bit longer than I thought and still has a couple of bugs:) I ran up 
> against a interesting problem I'll try and explain it in two dimensions:

Well, a crescent moon is just a half lit sphere. The outline is a 
circle, and the shadow line an ellipse. In the real world there are 
things like perspective to consider...you can probably ignore those 
here, though you haven't said what you were using it for. I'm not really 
sure what you're doing with those cones, or what kind of 3D shape you're 
looking for...just render a half-dark sphere if you want an actual 
crescent moon. For a 2D shape, you could use a polygon, thin prism, 
difference of cylinders, etc...just make half a circle, and cut out an 
ellipse with a major radius equal to the circle radius.


> Create a new circle with radius NewRadius such that when moved *from* 
> <-NewRadius,0> *to* <-MinorRadius, 0> points on the circumference pass 
> through points: <-MinorRadius,0>(obviously), <0,MajorRadius>, 
> <0,-MajorRadius>.

Sounds like you might be talking about a cycloid:
http://mathworld.wolfram.com/Cycloid.html

You want one "hump" of a cycloid with the ends at each point of a 
half-circle, and the peak at the peak of a smaller circle centered in 
the larger one? That doesn't really match what you describe, but it's 
the only way I can think of to get a crescent shape from a cycloid and 
circles.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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