Suppose I have a point on a sphere (R, t, p). The coordinates t and p could take on any value (you may assume they're both positive though), but I require that t be in the interval [0,2pi) and p in [0,pi].
How do I do this?
Thanks!
My attempt:
In the case of t, I can just do t%=2*pi. But p is a little more complicated, because if (for example) pi<p<2pi then p=2pi-p and t+=pi, but if 2pi<p<3pi then p%=pi, and t remains unchanged.
So I tried to extract a general algorithm for this, but I tested it and something's not quite right about it...
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Hmm. That seems to be a simplified version of my algorithm, and as such, I'm getting the same strange output.
I've programmed my owner rasteriser etc. for texture mapping a sphere. When I rotate it by incrementing t, the output is good:
http://www.youtube.com/wat
but when I increment about p, the output is odd:
http://www.youtube.com/wat
any ideas??
Well that's the problem I'm having, I can't quite identify the problem - it just looks odd, particularly the poles.
To check this, I've just rotated to look at the poles (by incrementing p to pi/2, and then I rotate t), and as you can see, the poles are never ending: http://www.youtube.com/wat
Now, p always represents the angle that is rotated horizontally on the screen, and t is always the vertical direction, so I'm starting to wonder if I'm doing this all wrong... Any thoughts?
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by: ozoPosted on 2009-09-16 at 10:29:51ID: 25347954
p%=2*pi
if p>pi:
p=2pi-p
t+=pi