cross ratio

noun Geometry.
a ratio relating four points in the real or complex plane.
Origin of cross ratio
First recorded in 1880–85
Also called anharmonic ratio.
Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for cross ratio
Historical Examples of cross ratio
The crossratio of four points equals that of the four conjugate points.
Before we draw conclusions from this result, we must investigate the meaning of a crossratio somewhat more fully.
If we take the points in a different order, the value of the crossratio will change.
It is convenient to let the point at infinity occupy the last place in the symbolic expression for the crossratio.
The crossratio of any four points in one equals that of the corresponding points in the other.