Relatively simple perspective question

[Steven Sweeney]

How did you place the two vanishing points ? Did you measure them to the right place or how?

Allan,

You are astute to ask this question. In fact, in my quick sketch, I just located the vanishing points where it was convenient to do so. More correctly, one would have to establish a so-called "circle of view", the radius of which is the distance from the viewer to the image plane (or drawing). From any point, then, on that circle, the vanishing points would be 90 degrees apart (using the point on the circle as the vertex of that angle.) This gives you an infinite number of available perspectives, though a relatively small number of them will produce aesthetically pleasing results, which for our purposes here is the primary consideration.

A caveat, that this is the procedure for the cubic polyhedron. Other forms require modification of this approach.

All of which is why I suggested that Ken focus on what he could see, with an eye to aesthetic considerations, rather than worry about precision in perspective.

[Allan Rahbek]

Hi, I just stumbled over this old tread and thought that I should try to make my point less brief by adding a practical example to show how the viewpoint, and angle of the view, affects the perspective in the final painting.
As you see, on the left illustration, the angle of view is about 75 degrees out of the full circle of 360 degrees. To project the correct drawing one would have to straiten out the curve before projecting the lines, but I cheated.

[Claudemir Bonfim]

Hi there,

Nice thread!

If anybody wants, I can email the pages in a larger size.

All the best.

[Claudemir Bonfim]

These are all from the book "Successful Drawing" by Andrew Loomis.

I've got many more pages about it.

[Claudemir Bonfim]

One might ask: "Why should I study about it? I paint what I see!"
First of all, painting is 90 % drawing.
Second of all, most painters paint what they "think" they see and not what the actually see.
Last of all, sometimes you need to paint a posthumous portrait, and in that case, the model cannot sit for you, so you have to use these rules to make a better job. Sometimes the lighting in a photograph is horrible, but you liked the pose, so, you can change the values, lighting, etc, if you master perspective.

Hope it helps.