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Ok, this one has me stumped. Maybe the smart people here can chime in.

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Well hello everyone,

I'm in a bit of technical trouble. I'm sure everyone has seen the large LED displays in China that have been all over the web for the past few months. Well, I'm trying to do the same thing. The basics are simple enough, take a photo from a predetermined vantage point, reconstruct geometry and camera, do the whole animation thing, render from reconstructed view and reproject onto the reconstructed geometry to bake onto a UV map. This has always worked for me in the past, but with screens that have right angles. Now I'm facing a curved screen, like in THIS example. My goto method has just stopped working. I can't get my angles right, everything seems bent as heck in real life. The funny thing is things DO line up when I take a photo of the screens from the predetermined vantage point.

My guess is that projecting on a curve isn't as straightforward as it might seems, but I've trying for a while now and I had little luck until now... In my hour of despair I turn to you, oh great wizards of vfx. Is there something I'm missing? Do I need another workflow?

I'm eager to listen to your wisdom!

 

Cheers!

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2 hours ago, konstantin magnus said:

Hi Michiel,

the UV texture-node offers a 'perspective from camera'-projection.

camera_proj.jpg.9d6ab520ce7f7ca931a00c8355947008.jpg

screen.hiplc

Hi constantin, thats, exactly what I've used. It also look fine when I project the baked texture back onto the geometry. But In real life I get bending like the first pic and When I take a picture of it everything lines up perfectly... Please note that I know my lens angle and position changes between these two photos. The first one approximates what you see in real life and the second one is from the vantage point I chose and how it SHOULD look in real life, but just doesn't.

 

 

IMG20210930131718.jpg

IMG20210930124503.jpg

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I have worked on such things before, (not with a round angle, but that doesn't seem to be the problem).
In my opinion there is a height problem in your reconstruction. It is always the same thing. Difficult to make virtual and reality coincide with large proportions.
 I guess you can't test live. My advice would be to make a movie where your image is still but where the "uv-project-camera" is animated and goes up in height in order to determine when, once projected in real life the perspective becomes correct. I know it's the geometry that should move, but it's easier and you can eventually transfer the difference you find to the model afterwards.
In any case, this is how I proceed when there is a problem of deformation and I can't act in live.
Even if you're not physically present the guy who make the test can tell you "Hey at 10s it's ok"

 

Edited by flcc

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On 16/10/2021 at 9:34 PM, flcc said:

I have worked on such things before, (not with a round angle, but that doesn't seem to be the problem).
In my opinion there is a height problem in your reconstruction. It is always the same thing. Difficult to make virtual and reality coincide with large proportions.
 I guess you can't test live. My advice would be to make a movie where your image is still but where the "uv-project-camera" is animated and goes up in height in order to determine when, once projected in real life the perspective becomes correct. I know it's the geometry that should move, but it's easier and you can eventually transfer the difference you find to the model afterwards.
In any case, this is how I proceed when there is a problem of deformation and I can't act in live.
Even if you're not physically present the guy who make the test can tell you "Hey at 10s it's ok"

 

Have you done some physical measurements for the reconstruction? spacial positions shooting point an screen, precise curvature of the screen...  Don't trust your eyes :)

Is it the lens conversion from your DSL to Houdini virtual camera correct?

 

 

 
________________________________________________________________

Vincent Thomas   (VFX and Art since 1998)
Senior Env and Lighting  artist & Houdini generalist & Creative Concepts

 http://fr.linkedin.com/in/vincentthomas

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Yes, for me at least measurements are taken with a laser, and the reconstructions are made to the correct scale. But sometimes that's not enough. Sometimes the measurements are just difficult to take without scaffolding and you have to trust the measurements you are given.
For example in the case of projection in most cases the technical guys give you the position where the projector will be installed. But in practice the projectors are installed a few days before the show. And when it comes to installing things that can be more than 50 kg at 10 or 20 meters high, well they are not necessarily placed exactly as they were told, etc. etc...

That's why I use the little method I described which works perfectly.

... and I trust only my eye :D

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I've solved my issue. The problem was I was waaay too close to the screen for my reference. Reconstruction was accurate, but the render was too distorted to be viewable, so I moved back some 30 feet and used a long lens (100mm) and everything worked like a charm.

 

Thanks everyone!

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14 hours ago, flcc said:

Yes, for me at least measurements are taken with a laser, and the reconstructions are made to the correct scale. But sometimes that's not enough. Sometimes the measurements are just difficult to take without scaffolding and you have to trust the measurements you are given.
For example in the case of projection in most cases the technical guys give you the position where the projector will be installed. But in practice the projectors are installed a few days before the show. And when it comes to installing things that can be more than 50 kg at 10 or 20 meters high, well they are not necessarily placed exactly as they were told, etc. etc...

That's why I use the little method I described which works perfectly.

... and I trust only my eye :D

ahaha I do too, but i force myself to do in the right order . Im by no way an image scientist :)

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45 minutes ago, nemsi said:

Hi Guys,

i'm begining a project for this kind of technical screen, Can you explain the process please?

Do I have to bake the screen (2 screens for angular LCD) like it's explained here?

https://www.adhaiwell.com/what-is-really-3d-led-display.html

 

Thank you.

Yeah, I've come across this when I was researching this. This is manufacturers bullshit. I've made a post about it over on the Blender Forums. I'll link it.

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1 hour ago, nemsi said:

Excellent!!!!

Thank you Michiel!!!

No worries! Took me two months to figure out all the steps to get it going.

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Quote

No worries! Took me two months to figure out all the steps to get it going.

I can agree with you.. ;)

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