MATLAB: Setting starting position of sphere.

sphere rotate

Hi, How can I set a default rotation position of:

[Xs Ys Zs]=sphere(80);

Best Answer

ZK, do you mean setting the sphere origin? If yes, simply add the coordinates of the origin:

 [x,y,z] = sphere(80);
 surf(x+1,y+2,z+3);

Related Solutions

MATLAB: How to find the normal to a hemisphere surface

Think about what the normal vector means. It points straight out from the hemisphere. What other known point is on the same line? (Hint: What do you know about the center of the sphere? What property does it have?)

That means, from ANY point on the surface of the hemisphere, call it [x,y,z], the normal vector is as simple as:

C = [2 1 3];
normalvec = [x y z] - C;

This vector is normal to the surface, and points outwards. Just negate the vector if you want it to be inward pointing.

MATLAB: Distance between two points on the sphere.

I guess you want to find the shortest distance along the surface of the sphere, not just the euclidean distance between the points. The shortest path between two points on a sphere is always located on a great circle, which is thus a "great arc". You can find Roger Staffords mathematically robust method here:

https://www.mathworks.com/matlabcentral/newsreader/view_thread/278872

For convenience I repeat it here too:

" P1 = [x1,y1,z1] and P2 = [x2,y2,z2] are two vectors pointing from the center of the sphere to the two given points (x1,y1,z1) and (x2,y2,z2) on the sphere, what is the shortest great circle distance d between them?"

 d = radius * atan2(norm(cross(P1,P2)),dot(P1,P2));

If you want an example of how to use this to generate points along a great arc, then see the Mfile colornames_cube in my FEX submission colornames. The nested function cncDemoClBk at the end of the file steps along a great arc, rotating the axes as it goes.

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Related Solutions

MATLAB: How to find the normal to a hemisphere surface

MATLAB: Distance between two points on the sphere.

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