Figure A-1 shows the basic construction to compute the image depth in ADCIGs based on the image depth in SOCIGs. Triangles and are congruent since they have one side common and the other equal because . Therefore, . Also, triangles AED and FCD are congruent because and also (, ). Therefore, the angle in triangle is the same as in triangle . We can compute from the condition
Figure 1. Sketch to show the computation of the image depth in an ADCIG.