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Method · junior member Member # Joined: 25 Jul 2004 Posts: 3

Hello everyone. Please excuse my English.

I have a question regarding the correct usage of perspective. See below:

As you can see, X1-3 follow guidelines towards the vanishing points, but when an object is rotated any number of degrees (Object Y1), no longer is it possible to accurately gauge what direction the contours of the object should recede. Do most artists just guess / approximate using their eyes and better judgment - or are there any concrete mathematical ways to correctly draw an object rotated x degrees? I'm guessing there is a way through the usage of a protractor. Any advice would be helpful.

Js
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Sumaleth · Posted: Sun Jul 25, 2004 1:15 am

I'd be quite interested to hear if there is a way to calculate where the VPs would be for that object based purely on that 3D view, but I've never come across a way to do that.

Usually if you were doing a layout like that you would begin with the top view, and project that down into the perspective layout. Using that approach you get the VPs for all objects in the scene.
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Art Links Archive -- Artists and Tutorials

Method · junior member Member # Joined: 25 Jul 2004 Posts: 3

Sumaleth · Posted: Sun Jul 25, 2004 2:00 am

Francis Tsai's tute explains it pretty well:

http://www.teamgt.com/forum/cubes01.htm
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AndyT · Posted: Sun Jul 25, 2004 2:02 am

I based a step-by-step tutorial on the one the Sumaleth posted.

I remember that it was hard for me filter out the info from one image ...
http://andyart.de/forum/index.php?showtopic=32
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Method · junior member Member # Joined: 25 Jul 2004 Posts: 3

Thanks much, very useful. Looks like I need a larger drafting board.
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cyBeAr · Posted: Sun Jul 25, 2004 3:45 pm

If you know/have decided what a square looks like in your perspective system you should be able to derive everything for that although I'm not sure it would be more convinient to use than a projection.
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cyBeAr · Posted: Sun Jul 25, 2004 5:09 pm

Ok I'll try to explain how to do it altho I'm probably too tired to make ane sense.

Freehand/eyed linetool picture:

Ok so the blue area is supposed to be a square in perspective wich we will base everything else off, it's sides go off to the two known vanishing points. By drawing a line from one corner of the square and then through the opposite corner off to the horizon we get a 45 degree vanishing point wich can be very usefull for meassuring things, I drew both 45degree vp:s but actually only used one.

I picked a corner of the square (O) to work from (doesn't matter wich) and drew a line through it non-parallell to our ealier vanishing points. For this example I used a random angle - if you have to have a specific angle you have to work out or make a good guess of where to put point A to get the desired angle between lines OP and OA.

To get a line OB that is angled 90 degress from the line OA we need to find the right place for point B, and that is easy because the distance BQ will be the same as PA (from a topview) so now we just have to transfer and turn the distance PA in perspective to where we want it.

Argh I'm just not in the state to explain the rest in a way that can be easily followed atm so I'll leave it to figure out from the pic and if you don't understand I guess I have to come back and try again.

This explaination turned out really bad but I'm pretty sure the theory behind it is correct... too bad my pedagogoic skills weren't any better.
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agflash · Posted: Mon Jul 26, 2004 2:30 am

Also check the Loomis-Books
Especially "Successful Drawing":
http://www.fineart.sk/index.php?s=24&cat=15
^^