Vanishing points beyond the edge of my desk

[brocksamson]

I've been searching for a way to handle perspective on objects whose vanishing point(s) extends beyond the edge of my desk and would require a ridiculously long ruler. Yet I don't want to be confined to keeping the vanishing points within my drawing surface. Does anyone know of a professional trick to handle this? And preferrably something that allows me to still use a straight edge to bang out several lines in a row, keeping one end anchored (as opposed to having a perspective grid underlay, but still no place to anchor the ruler)?

[Christian223]

http://onlinebooks.library.upenn.edu/webbin/book/browse?type=lccn&key=NC

Check the book "the theory and practice of perspective" there is a section that teaches a "new" method of doing perspective that is the one you are looking for. Good luck.

[armando]

A trick Scott Robertson gives is a sort of estimation of angle. The first two vanishing lines you place are arbitrary, but their angle should be small enough that they would hit the horizon some distance off your paper or desk. After you've chosen those two lines, then you try to match their angle with the next ones you put. Measure your accuracy by scanning the image then shrinking it down. You could also draw a small but accurate perspective grid then scan it and print it out at a bigger size. Another way is to pick points somewhere off your paper, then while staring at said point try to aim your lines towards it.

[brocksamson]

Thanks guys, this is just what I'm looking for. I'm new to this board, and I appreciate your willingness to help! Christian--The link to the book is great, especially for precise geometry I need to project in space and understanding how to extrapolate secondary vanishing points from a single line (I feel like a moron for never having come across these techinques in my searches) and armando I appreciate the your suggestion esp. for background jobs that I'd like to fake with a good amount of perceived accuracy. (I like your avatar--based on the best mugshot ever taken!).