Normal Disappear Problem
- To: mathgroup at smc.vnet.net
- Subject: [mg55302] Normal Disappear Problem
- From: "gouqizi.lvcha at gmail.com" <gouqizi.lvcha at gmail.com>
- Date: Fri, 18 Mar 2005 05:35:18 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Hi, All: I have the following parametric equation for an unit sphere: x = cos(u)sin(v) y = sin(u)sin(v) z = cos(v) 0<=u<2*Pi ; 0<=v<=Pi Then I use normal = (Dx/Du, Dy/Du, Dz/Du) CROSS (Dx/Dv, Dy/Dv, Dz/Dv) to get the normal vector. I get the follwoing after calculation (with normalization): normal = [sin(v) ^2 cos(u), sin(v)^2 sin(u), cos(u)^2 cos(v) sin(v) + sin(u)^2 cos(v) sin(v)] Now when u=0, v=0 , Normal = (0,0,0)! How can it be? We know the fact that a sphere should have normal everywhere. Rick
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