OF THE MEASUREMENT POINTS
Mark the vanishing points 1 and 2 and the depth point on the horizon line.
Also on the horizon line, mark the measurement points 1 and 2, (square measures) 2cm away from the view point. Place one point at the right and the other at the left.
Repeat the operation on the support line or measurement lines – 2cm at each side. Join the points forming an X, as shown at right.
At the crossing of the lines that run to vanishing points 1 and 2 with the lines that run from the support line to the measurement points 1 and 2 we will find the measurements of the horizontal plane.
See illustrative figure below: