Topic: get center and radius of sphere by picking 3points

[motee-z]

Hello friends
any help for a lisp to get center and radius of sphere by picking 3d  3 points
thanks

[ribarm]

You meant 4 points - not coplanar?
3 points are needed for creating circle - do you need sphere with circle as equatorial parallel...

[motee-z]

In autocad we use 3point in space not in the same level
But i know in mathemtic in we need four point in space to creat sphere so i dont know which is true

[57gmc]

When you say "get center" do you mean find the properties of an existing sphere? All you would need is a single selection. Or do you mean, create a sphere?

[motee-z]

I need to get coordinate of center of sphere to draw the point of center because l have a lot of points on a shape i think it is a sphere so i want to pick necessary number of points then draw the center point of the sphere as point and get alert that radius is this all this without drawing the sphere if possible

[motee-z]

Ok if can,t get the answer can be know how to extract the information above from dxf code of a drawen sphere

[ribarm]

Sphere as 3DSOLID entity has center point (vla-get-center VLA-OBJECT)... But if you need to create SPHERE, you haven't answered to my question - 3 points in WCS give circle - do you want sphere from that circle, or 4 points not coplanar whereas each triangle has normal xline through center of circumscribed triangle and at intersections of those XLINEs, you obtain center point... Radius is pretty easy : R=(distance cenpt pttriang)

[motee-z]

Ok from 4 points