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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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