3D proportions tutorial

[Khris]

I browsed through the Critics Lounge yesterday and found an old thread about a problem with perspective.

So I made a short tutorial on how to get the proportions right. It can be found here.

C&C welcome

[Hollister Man unplugged]

Nice job, although your 'cube' looks a bit too stretched out.  I'm sure the geometry is correct, but it just doesn't look like the perspective is realistic.  I'm not sure what would cause this though.

[Khris]

I explained the reason for the distorted look of the cube in the end of the tutorial.
A quick drawing to illustrate what happens when the eye is moved down:

[Pelican]

Don't be offended, but I found the tutorial terribly confusing. A lot of stuff about perspective and vanishing points, I've worked out myself simply from looking around me, and reading some threads in the critics forums. With your tutorial, I didn't really understand what the overhead view was meant to be illustrating. Perhaps a little more elaboration might help?

[RickJ]

Thanks khrismuc.   A while back I spent quite a lot of time trying to figure out get the Z-axis right in a perspective drawing.  I got as far as the "triangle/equal distance" thingy but could never figure out how to translate an x or y distance into a z distance. 

I am still a little confused about the relationship between the top view and 3d viewport as far as some of the inital conditons are concerned.  Probably a bit more comentary and what-if's would be helpful.     

[Khris]

Thanks for the feedback, all.

A better name for the tutorial would have been: "How to translate a 2D top view into a 3D front view".

I also admit that I focused on the visual aspects. The textbox could have been bigger, the explanations more detailed.
The tutorial was made to show how to get the Z-axis right and was thus aimed at people who already have experience with vanishing points and perspective.

I'm to lazy right now to change the tut, but maybe this helps, anyway:
- The distances that I used can be varied freely. Just experiment.
- The top view and 3D view are only connected by vertical lines, so it doesn't matter how far above the top view the 3D one is.
- The grid is, of course, optional.
- Check my 3rd post in this thread. In the 3D view, the red line is where the 'viewscreen' hits the ground. As the viewscreen has no depth, it is only a line in the top view.
- A point that has the viewscreen's Z-coordinate can be translated 1:1 to the 3D view.