Parent Article: DrawIn3D.htm 
We call lens transformation ...  
Isometry 

 
We call lens transformation:

   r~R/Z, 

where 
   r=(x,y) - human eye bottom or monitor screen coordinates,
   R=(X,Y),
   X,Y,Z - coordinates of point in "3D World" to be projected to a screen,
   Z axiz is perpendicular to a screen.
   


Here are more details. (Choice of Z-axis is different than above.):

Sketch 0 0
Sketch 0 1