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Author   Topic : "Perspective rotations tutorial"
T_England
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Joined: 24 Feb 2009
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PostPosted: Sat Sep 11, 2010 6:39 pm     Reply with quote
I did this for a friend a while back after I failed at trying to explain it over MSN. I noticed a lot my concepts ended up with objects perfectly perpendicular to each other,
i was finding it really difficult to retain a correct lens when rotating an object, this photoshop method allows you to keep vanishing points at the same relative length.

I still don't know if any of this is actually true though. I checked out the perspective stuff on handprint.com and it went waaay over my head, i traced over 3d software
to try and find a pattern in the way they maintain perspective and there seems to be some perspective correction stuff going on.

Anyway i hope it helps someone, and i would especially appreciate anyone who knows about this stuff to chime in and offer any corrections, i cant seem to find much useful
perspective theory on the internet without it being either too simple or too technical to be practical.




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durgldeep
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PostPosted: Sun Sep 12, 2010 1:10 am     Reply with quote
Yikes, am only vaguely aware of lens issues atm.
Good to see a diagram (and useful heads up, for me). Smile
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Sumaleth
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PostPosted: Sun Sep 12, 2010 3:10 am     Reply with quote
That is an approximation that will only work if the angles are similar. A more robust approach is to draw the objects in plan and project down to find the vanishing points. This shows how the plan is used:

http://www.khulsey.com/perspective_2pt.html

Francis Tsai posted a good example many years ago, with multiple objects at different rotations, but it's long since gone. This is still only an approximation, and I can't remember if this approach breaks down at the extremes, but I remember finding it worked pretty well.
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T_England
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Joined: 24 Feb 2009
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PostPosted: Sun Sep 12, 2010 7:46 am     Reply with quote
Oh yeah i have seen that method before, i think i even tried it once but found the construction a bit unwieldy i should probably go through it again so at least I'm not ignorant of it, I do agree with you though, I noticed the wider the lens the more acute the rotation the more things fall apart and such.

I guess at first it helps keep things square but after really will have to take into account distortion. I haven't seen the method Francis Tai outlined id be interested though

I suppose i'm aiming for "within acceptable tolerance" I need to understand lenses more and intuitively take into account distortion and correction.

Spooge got me thinking about lenses more in this tutorial he wrote years ago, its great as it deals more with drawing errors and problem solving.

http://www.gfxartist.com/features/tutorials/7840
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neff
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PostPosted: Mon Oct 11, 2010 11:32 pm     Reply with quote
I prefer Google SketchUp Wink
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