Preserved Topic: perspective, horizon, distance (Page 1 of 1)

Some time ago Doc, Weadz and DG went on a perspective kick that blew my mind. They showed me how to draw a horizon line and set perspective points for 1, 2, 3...even 4 point perspective. All of that was fun and I've been doing some experimenting with this.

This has added a dimension (please pardon the pun) to my (still meager) drawing skills I never had before...

Next question:
How do I determine distance out toward my vanishing point?

If I am standing on a sidewalk I notice the blocks of concrete appear to get smaller and smaller with distance. I know the blocks are (roughly) the same size.

If I am drawing this scene, is there a way to accurately draw my horizontal lines (defining each concrete block) along the sidewalk so it matches the perspective of the rest of the scene?

I can figure out qualitative patterns:
far = closer set lines
near = further set lines

horizon line high = lines get closer at a 'slower' rate as they are further from me
horizon line low = lines get closer at a 'faster' rate as they are further from me

...but I'm having trouble translating these qualitative patterns into something quantitative.

Any advice?

mobrul: I think you are onto the principle and I remember we did something like this in school with a railway line going into the distance. What you've said is really something similar to exponential growth so you should be able to draw a graph - in fact the one I'm thinking of is the growth of daughter atoms in radioactive decay and there is a nice applet here:
http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html

its the blue line. If you were to treat the x-axis as the regular spacing of the paving slabs or railway sleepers then you draw the lines up to the blue line and across to the y-axis then this would come close to simulating the effect - you would find the lines starting off evenly spaced and slowly drawing closer to each other.

Sorry if that is a little messy as I was thinking outloud and developing my thoughts as I went along but that is the way I'd try and mathematically model it (just adjust the curve to suit).

Also on the old dicsussion - perspective FAQ:
http://faq.ozoneasylum.com/207/

___________________
Emps

FAQs: Emperor

Here's a bit of a tip to help out on bricks, windows etc. etc. It's basic as hell and will need thought and tweaking when you try and apply it, but keep it in mind to start off.

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1. Make a block area. I've used a 500 px X 500 px square here. This will define your vanishing limit as well as your end wall.




2. Establish your vanishing point, and the top and bottom lines of your walls by drawing lines from the vp to your extremes.




3. Since your bricks will all have the same height at your eyeline, we set even spacings for them, and draw our perspective lines from the vp.




4. Now for the catch. Draw a line that runs from corner to corner of your establishing block area. You'll understand the line in a second.




5. Now at every point that the diagonal (red) line intersects one of our perspective lines, draw a vertical line down the "wall".




6. Erase your superfluous perspective line areas, and voila....walla. ~grin~




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Sorry it's so damned fast today, but I'm in a rush. Hopefully I can get back to this thread for other little tips and tricks

Peter

Lasciate ogne speranza, voi ch'intrate

Sheesh. You guys and your "calculations"


heh - I always just eye-balled it. That's a cool trick though Peter...probably would have saved some erasing back in the day.....

{{edit - ok, so the first question that went through my head was 'how do you determine the spacing if you need to continue the lines?'

So I did this example to make sure I had it right...so in case I'm not the only idiot that had to actually think about it -



Add a baseline horizontally through your last vertical line. Draw the reference line from that intersection to the same corner the original line came from...and repeat...}}




[This message has been edited by DL-44 (edited 06-18-2002).]

Yep yep yep.

Hence the "think" part. Good show.

and multiple constraining boxes from your lines will yield the ability to do perspective offsets (gaps between the "bricks" as well). It's a good trick when doing cityscapes in detail ~groan~



[This message has been edited by DarkGarden (edited 06-18-2002).]

Good stuff, gentlemen. I knew there was a way besides eyeballing and erasing.

You have a unique gift, Peter, for putting into words what my hindbrain knows, but won`t tell me.
Can I download that somewhere ?

Coolness...this should find its way into the FAQ...thanks DG and DL-44....ya just gotta love these guys...

Thank you.
Always wonderful stuff coming from you.

And, though it is not anywhere near a finished point, I wanted you to see the basic 'sketch' of my playing with perspective.

Sorry about the geocities...only thing I can afford right now

Thank you again.
I'll post again as the picture becomes more complete.

mobrul

Hhhmm.. Interesting, I like it!!

mobrul: Try here for hosting ideas

This has now been added to the FAQ - great stuff and a big thanks to DG and DL:
http://faq.ozoneasylum.com/647/

___________________
Emps

FAQs: Emperor

Yes, definitely great stuff! With entries like this, our FAQ may very well end up becoming the premiere source of knowledge on the Net. OK, so that may be a slight exaggeration...

Mobrul - one suggestion: the boards(?) in the front seem to have a different vanishing point than the 'path' that leads toward the back, which throws everything of a little. It seems almost as if the path is going upward as it goes back, but if that's the intention, it seems unrealistic to do so in such a straight smooth manner.

Even though the fornt part appears to be curving around the front, all the pieces should still have the same vanishing point.

Aside from that, it looks good.

Alright, DL (or anybody else who cares to answer), I have some questions.

The idea was to get the appearance of a wide-angled lens...perhaps I curved stuff too much?
You can see a bird's eye view of the desired scene here.

I also wanted the path to seem angled a bit to the right...my thoughts were this required a 4th vp. Is this correct? This perspective thing is great, but it's a lot tougher to figure out the details...maybe I should start with something simpler...like a box -- a plain cardboard, featureless box.

Is my 'theory' correct? I still want to do the details, but I want to make sure my horizon line, vanishing points, and general lines of perspective are 'correct' before I proceed any further. My eye is good enough to know something is wrong...but my brain doesn't know what it is -- yet.

Thank you
mobrul



[This message has been edited by mobrul (edited 06-26-2002).]