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

[motee-z]

here is the lisp that can draw the single sphere that passing 4 points

Code - Auto/Visual Lisp: [Select]

1. ;by engineer motee malazi syria
2. (defun c:sp4p (/)
3.   (setq P1(getpoint"\ pick FIRST point OF SPHERE "))
4.   (setq P2(getpoint"\ pick SECOND point OF SPHERE "))
5.   (setq P3(getpoint"\ pick THIRD point OF SPHERE "))
6.   (setq P4(getpoint"\ pick FOURTH point OF SPHERE "))
7.   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
8.   (setq osmd(getvar"osmode"))
9.   (setq A1(CAR P1)
10.         B1(CADR P1)
11.         C1(CADDR P1)
12.         )
13.   (SETQ E1(-(+(* A1 A1)(* B1 B1)(* C1 C1))))
14.   (setq A2(CAR P2)
15.         B2(CADR P2)
16.         C2(CADDR P2)
17.         )
18.   (SETQ E2(-(+(* A2 A2)(* B2 B2)(* C2 C2))))
19.   (setq A3(CAR P3)
20.         B3(CADR P3)
21.         C3(CADDR P3)
22.         )
23.   (SETQ E3(-(+(* A3 A3)(* B3 B3)(* C3 C3))))
24.   (setq A4(CAR P4)
25.         B4(CADR P4)
26.         C4(CADDR P4)
27.         )
28.   (SETQ E4(-(+(* A4 A4)(* B4 B4)(* C4 C4))))
29.   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
30.   (SETQ B5(/(-(* B1 A2)(* B2 A1))A2))
31.   (SETQ C5(/(-(* C1 A2)(* C2 A1))A2))
32.   (SETQ D5(/(- A2 A1)A2))
33.   (SETQ E5(/(-(* E1 A2)(* E2 A1))A2))
34. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
35.   (SETQ B6(/(-(* B2 A3)(* B3 A2))A3))
36.   (SETQ C6(/(-(* C2 A3)(* C3 A2))A3))
37.   (SETQ D6(/(- A3 A2)A3))
38.   (SETQ E6(/(-(* E2 A3)(* E3 A2))A3))
39.   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
40.   (SETQ B7(/(-(* B3 A4)(* B4 A3))A4))
41.   (SETQ C7(/(-(* C3 A4)(* C4 A3))A4))
42.   (SETQ D7(/(- A4 A3)A4))
43.   (SETQ E7(/(-(* E3 A4)(* E4 A3))A4))
44.  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
45.   (SETQ C8(/(-(* C5 B6)(* C6 B5))B6))
46.   (SETQ D8(/(-(* D5 B6)(* D6 B5))B6))
47.   (SETQ E8(/(-(* E5 B6)(* E6 B5))B6))  
48.   (SETQ C9(/(-(* C6 B7)(* C7 B6))B7))
49.   (SETQ D9(/(-(* D6 B7)(* D7 B6))B7))
50.   (SETQ E9(/(-(* E6 B7)(* E7 B6))B7))
51.   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
52.   (SETQ M(/(-(* E8 C9)(* C8 E9))(-(* D8 C9)(* D9 C8))))
53.   (SETQ W(/(- E8(* D8 M))C8))
54.   (SETQ Z0(/(- W)2))
55.   (SETQ V(/(- E5(+(* C5 W)(* D5 M)))B5))
56.   (SETQ Y0(/(- V)2))
57.   (SETQ U(/(- E1(+ M(* C1 W)(* B1 V)))A1))
58.   (SETQ X0(/(- U)2))
59.   (SETQ R(SQRT(/(+(* U U)(* V V)(* W W)(* -4 M))4)))
60.   (setvar"osmode"0)
61.   (COMMAND"POINT"(LIST X0 Y0 Z0))
62.   (setvar"osmode"osmd)
63.   (command"_sphere"(list x0 y0 z0)R)
64.   (PRINT(LIST X0 Y0 Z0))
65.   (ALERT(STRCAT"RADIUS="(RTOS R 2 3)))
66.   )

[motee-z]

autocad can draw sphere from 3 points but there are many spheres can pass three points