Advice for projection on building facade

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Advice for projection on building facade

Postby ppfer » Fri Jan 16, 2015 5:18 pm

Hi. I was hired to project on a building facade and also to produce some 2D content.
I'm quite new to this. The facade is not very complex, quite small and architectural elements are relatively flat but - for various reasons - the projector will be placed with the lens aligned to the top of the facade so I will need to use lens shift and - probably - slightly distort.
I need an advice on how to take a reference picture for content production to achieve the best result once in PB warper.
I should take the picture from the projector point of view (which will produce a quite distorted image since it's taken from top to bottom) and work on a distorted reference or - as I guess - it's better to take it from the viewer's point of view which is likely to produce a more flat image and then correct the distortion in PB warper?
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Re: Advice for projection on building facade

Postby claude.rivet » Fri Feb 13, 2015 7:40 pm

I will try to answer as best as I can given the provided infos but here goes:

-first working with pictures is kinda tricky but it can do the trick, the problem lies in both the geometric distortion of the lens and in the perspective distortion of the focal lenght characteristic of the camera versus those of the lens of your projector. If you want to work with pictures I very highly suggest also taking some measurement of key points in your façade. Once you know the wall is 30 feet high by 20 feet wide and that the first window bottom center is at 8 feet from the ground and at 10 feet from the side and so on and so forth it is easy to correct the image and then work on it to produce content.

-You HAVE to place the camera where the crowd will be because the picture will have the correct perspective (if you place the camera at the projector, which is on top, it will see the top of the features found on your façade whereas the crowd will see the bottom, the illusion will be broken).

-Then take the image and using the good measurements undistort it and flatten it, your people can then work on a flat wall.

-Then once you are ready to project use the picture as your mesh texture and activate plannar mapping. Map your wall using a mesh and do not bother with the features found on your façade.

-Then cut out every feature of you façade that protrude or goes in, basically all feature that are not on the same plane as your wall. Mask their surrounding as the cut out will always be rectangular, then place them where they should be and warp them individually.

That should provide you with a good enough result. If you try to warp the wall with only one mesh you will quickly realize that the result will be extremely distorted, it should be done individually. Every single item that is not on the same level as your wall won't be correctly placed, it is garanteed because the distance travelled by the light is not the same and therefore at this location the image is of the wrong size.

Hope this helps!
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