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Old 13-08-2007, 03:54 AM   #1
peri
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Default Vertical Perspective Problem

Is there a way to 'force' Maya to use 2 point perspective?

I'm trying to model a scene by Piranesi. As you can see, he uses standard 2 point perspective with 'true' verticals.
The left and right vanishing points match up pretty much ok, but Maya's verticals are way out - getting worse towards the edges of the reference.. I've tried altering various camera settings, but i can't even get close.

Any tips or suggestions would be really appreciated.

Thankyou

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Old 13-08-2007, 05:14 AM   #2
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Hello Peri bare with me, this is going to get lengthy and technical.
Anything outside the 90 degree cone of vision is going to be distorted. That's unavoidable due to physics/laws and perception of perspective. Human eye have roughly 50-60 degree cone of vision. But dispair not. We can straighten those verticals out.


Here's a trick from Maya 6 killer tips:
Perceptual Perspective Correction
A long-standing technique preferred by architectural illustrators and large-format photographers is to eliminate the third vanishing point while maintaining the position of the horizon line and key features.
This amounts to effectively straightening out the converging vertical lines a camera would see as it tilts skyward. While looking upward at a very tall structure such as a skyscraper, this phenomenon is unavoidable, but with lower structures, or even in a room, your brain compensates for the optical taper, keeping vertical lines parallel and delivering a perceptually correct view.

You can test this out simply by tilting your head up towards the ceiling as you watch a corner of a room. Now do the same thing with a camera and observe the effect.
Although the tapering is optically correct, being able to eliminate it in a 2D image such as a photograph or CG render creates a much more pleasing and refined look.

Maya luckily has included the virtual analog of a perspective shift lens in a commonly overlooked attribute in the Camera Attribute Editor called Film Offset. Of little use in animated cameras (except for excellent abstraction potential), it shifts the virtual film plane in screen space x or y a given amount.

To start, position a camera near the bottom of a tall building-shaped cube. Use the local camera command Panel View, Camera Tools, Yaw-Pitch Tool to then tilt upward, setting the horizon line at a given position. Next, under the Camera Attribute Editor, Film Back, Film Offset, type in an arbitrary number such as .3 in the second field (y). The horizon will shift down below frame, but raise it back up to the same level with the Yaw-Pitch Tool.

Now you will have the same view, but with parallel vertical edges. If it is not yet parallel, try increasing or decreasing the Film Offset value and Yaw-Pitch accordinly. Your still renders can now look much more refined with this great technique.

For something really wild, increase your field of view to a very large value and add Film Offset to both x and y. Now tumble the camera through your own version of Hitchcock's Vertigo!
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Last edited by AlphaFlyte : 13-08-2007 at 05:18 AM.
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Old 13-08-2007, 05:24 AM   #3
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Thank you very much - that looks to be exactly what i need. I'll try it this evening when the house is quiet.

Thanks again mate.
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Old 14-08-2007, 01:57 AM   #4
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I finally managed to get vertical uprights by increasing the focal length of the camera to 150 and then zooming back in, and using the offsets to centre the picture. Now the left and right perspective is out haha.......is there an established procedure for working out the position of the grid?

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Old 14-08-2007, 02:07 AM   #5
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You might need to see if you can get any info on the camera that was used to take the shot and then dial the settings in the attribute editor.
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Old 14-08-2007, 03:08 AM   #6
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Try to keep the cameras focal length to 90 for as long as its possible. A true to space, undistorted perspective.
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Old 14-08-2007, 05:27 AM   #7
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Thanks for the replys - all help is appreciated.

gster - its a drawing by an 18th centuary italian artist, no cybershot info available i'm afraid
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