Perspective Projection Drawing How to


#1

I’m trying to create a Perspective Projection drawing like this one in Rhino 5:

I know it sounds a bit weird (it’s an assessment issue in my country (NZ)).
I’m basically trying to reverse enginieer the drawing in image D above out of a building model.

So far it all works fine. The only part I’m having difficulty with is setting up (image B). I have to set the vanishing points parallel to the edges of the building.

I’m using the 2 Point Perspective view (thanks for that by the way!)
I’ve set up a station point (using the ‘place camera and target’ tool)

I’m now trying to set up the viewport properties (particularly the lens length), but I don’t know what lens length to use to get the 90 degree viewing angle.

Is there a better (quicker =) way of doing this?

Hope that makes sense.
Thanks for your help


#2

Have you played with Perspective Match?


#3

Well, “lens length” is based on the diagonal of a 35mm film frame - 36mm x 24mm… It’s just a matter of drawing out the triangle and measuring the angle (or using a little trig)… A so-called “normal” lens is around 50mm, giving an angle (Field of view, FOV) of 46.8 degrees. So a 90 degree view angle is pretty “wide-angle”. Given that half of 90 deg. is 45 deg. and a 45 deg. triangle has equal legs, you can do the math with a calculator :

Diagonal of 24 x 36 frame: sqrt( 24^2 + 36^2) = ~43.267 mm
Lens length = diagonal/2 : ~21.63 mm

–Mitch


#5

Thanks, that’s very helpful
Andrew


#6

Thank you both,
I’ve done some more testing and it turns out that the lens length and perspective angle don’t really matter. It works at any angle or length it seems. The only difference is how much of the object that you see. The wider the angle (or shorter the lens length) the smaller the object appears in the view port.
This seems to be a feature of two point perspective in Rhino. Not sure how it works that way, but I’m happy that it does.

Once I do some more testing to make it full proof, I’ll be telling my students to set their viewing angle to 45 degrees. (they can then scale the drawing as needed).
Andrew