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

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.

[John]

Look up 'sphere' in the MATLAB documentation. It is straight forward.

[jiji hr]

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 ?

Answer 1

[KSSV]

[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)

[jiji hr]

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.