how to plot a unit sphere around a 3D object ?

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jiji hr
jiji hr 2016-6-8
评论： jiji hr 2016-6-10
Hi,
I am actually working on 3D objects (.obj files), and I am trying to define à unit sphere on a 3D object, but I really don't have any idea how to do it and even how to searche, I don't know if it existe on matlab or should I see an other softwar. I want to obtain something like on this image:
Could you help me please.
  2 个评论
John
John 2016-6-8
Look up 'sphere' in the MATLAB documentation. It is straight forward.
jiji hr
jiji hr 2016-6-9
the problem I encounter is that how to center it on the object so that I could aligne objects acourding to this sphere with PCA,what ever its size ?

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回答（1 个）

KSSV
KSSV 2016-6-9
编辑：KSSV 2016-6-9
[x,y,z] = sphere ;
surf(x,y,z) ;
Generates the sphere with origin as center. If you want the center of sphere at [x1,y1,z1], (your desired center, which will be at half the length of your object) just add this point to [x,y,z].
[x,y,z] = sphere ;
xnew = x+x1 ; ynew = y+y1; znew = z+z1 ; % shift the origin to [x1,y1,z1]
surf(xnew,ynew,znew)
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jiji hr
jiji hr 2016-6-10
Actually what I was searching about is to draw the minimum bounding sphere around each object in my DB, because the matlab's sphere function is just for drawing a sphere. In the literature there is a lot of algorithms to compute the minimum bounding sphere such : Gärtner's algorithm, Welzl's algorithm, Megiddo's algorithm, Fischer's algorithm ... And fortunately I found one of these algorithm in File extchange, and here is the link : Exact minimum bounding spheres/circles I would like to thank you for these informations about sphere too, and I wanted to share these informations about minimum bounding sphere algorithm, may be it will be helpful for some one in the same situation as me.

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