3D Trick to Draw Perfect Arch in One Point Perspective (Narrated in spanish)

Hello friends, here you have a new trick of drawing in 3d and perspective of a point. How to draw perfectly proportioned Roman Arches very easy and step by step.
It is narrated in Spanish, but we would appreciate your help to do the subtitles in English;)
Video music:
www bensound.com
Visit my blog (in Spanish): retratarte.org