Basics of Coordinate Metrology
Unit 4:  Geometric Elements - Sphere

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The next standard geometrical element is the sphere. A sphere has all area points at the same distance R from a fixed point P. A sphere has the following characteristics:
Extension: Radius R
no direction

A sphere is determined by at least four (probing) points (on the sphere surface). These points are used to calculate the center P (x, y, z). The distance from the center to each of the (probing) points is called radius R.

In practice the diameter (Ø) D is usually used instead of the radius R. It is twice the value of the radius (D = 2 R).

 

Important: The points used to calculate the sphere must not be on a circular line. Ideally the points are distributed on the sphere such that they probe both the poles and the equator of the sphere.

 

       

Element:
Sphere
Display:

Parameters:
center P (x, y, z), 
radius R
Required minimum number of probing points:
4 probing points
Example using a part:

(Trailer hose coupling)