The horizontal length is unchanged, and the vertical length is half of the original drawing.

Because O 1D 1 is parallel to O 1Y 1, D 1 is on the y axis.

The original picture is a right trapezoid.

Up and down DC=3

Bottom AB=2

A 1D 1= 1 The restored original image is AD=2.

Upper bottom plus lower bottom times height divided by two.

(3+2)×2 into 2 =5

Another formula is

Area ratio of orthographic image to original image = root number 2 to 4.