Limits of sphere to obtain points

Hello everyone!

I have multiple points (nodes). And i plot (plot3) a sphere with coordinates of center x0,y0 and z0 with radius r. I need to obtain the points (nodes) which are inside in sphere. How i can do this? How i can obtain the limits of curvature of sphere (in x,y and z)?

Thanks!

code:

[x,y,z] = sphere();
plot3(r*x+x0, r*y+y0, r*z+z0,'k-')

[Walter Roberson]

What data structure do you have to describe the nodes? For example is it a struct array each element of which is a structure with elements 'x', 'y', 'z', each a scalar?

[Nuno]

I have the coordinates of nodes (x,y and z) And with this i represent them in plot3

Answer 1

[Walter Roberson]

All of those nodes are on the outside of the sphere. None of them are inside the sphere.

[Nuno]

why?

[Walter Roberson]

Because that is how the returned values of sphere are defined: they give coordinates of points on the surface of the sphere.

I suspect what you are trying to do is find the points that are inside the boundaries of a sphere drawn inside a cubic lattice, sort of the three dimension equivalent of the coordinates of the pixels inside a circle drawn into a two dimensional image. But in order to do that you need to define the size of your pixels as there would be many more pixels if the grid was -r:1/100:+r than there would be for -r:1/10:+r

[Nuno]

I have about 654,000 points. And, for example:

I want to draw (in plot3) a sphere at the center x = 169; y = 215; z=216 with radius 19. The points that are within a sphere, I can not know what?

I do not need to know the sphere limits / boundaries and then with a loop through the array (that have all the coordinates x, y and z of points) and see what are inside the limits?

[Walter Roberson]

If you have a specific list of x, y, z and you wish to know which are inside the sphere then

insphere = (x-Xcenter).^2 + (y-Ycenter).^2 + (z-Zcenter).^2 < Radius.^2;

and the corresponding points are

xin = x(insphere);
yin = y(insphere);
zin = z(insphere);

[Nuno]

Thanks ! I will try

[Nuno]

Work i guess :D

[Nuno]

VERY THANK YOU Walter :D