Positions of LEDwall and Virtualwall do not match

 

I have a question about LEDwall based VirtualProduction.


( https://aximmetry.com/learn/tutorials/for-studio-operators/using-led-walls-for-virtual-production/ )

Work progressed smoothly based on the above tutorial.

However, when overlaying LEDwall and VirtualWall, a gap will inevitably occur.

Therefore, the boundaries are unnatural.

When the camera is facing the front, it almost matches, but when you pan or tilt it, the more you go to the outside of the monitor, the more it shifts, and when it comes to the center of the monitor, it matches.

Camera Calibrator and Floor Calibration are already set.

The distance from tracker and camera to LEDwall is accurate. The size of the LEDwall is also accurate.

I am using VIVE Tracker.

Do you know the reason?  Is there any other data you need? Is it content that always causes gaps?


https://drive.google.com/drive/folders/1NhC8y1BwtXKVQxPRmk-aAIF4tWVZ1YZn?usp=sharing


waiting for your reply.


   TELMIC

 
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TELMIC
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I have a few additional questions.

Is the LEDwall position the actual measured distance? Or did you enter the value manually while looking at the monitor?

Is there a basis for the LEDwall Radius value? Is the value entered manually while looking at the monitor correct?

 
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TwentyStudios
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For this to work, the camera tracking and lens calibration needs to be really, really accurate. I don’t think standard Vive trackers are up to the job. It also looks like the timing doesn’t match. Since there is no genlock on Vive Trackers it will be hard to get the match close enough. Finally, do you have any stabilization active on the camera or lens? That must be turned off for camera tracking to work. 

 
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TELMIC
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Thank you for your reply. We understand that VIVETracker is difficult to tune. We can use OptiTrack. We have 3 Flex3s and they are often difficult to recognize.

https://www.optitrack.jp/products/camera/flex3.html

 
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Eifert@Aximmetry
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Hi TELMIC,

Vive can produce a much better result than in your videos.

There is some strange shaking going on that can be a problem with the tracking or the video or the stabilization being active as TwentyStudios said. It is hard to determine what is causing it from the videos.


Also, it seems your Led wall's Transformation, Size, Radius, or Resolution is not set correctly:

LEDwall Radius sets the curve of the led wall. Since it seems you have a curved led wall, you must change the LEDwall Radius value to one that will fit the virtual led wall exactly onto your real-world led wall.

You should do this while this button is turned on:

After this, you should change the values in the Led Wall panel until the pattern displayed by the led wall matches up in position with the pattern in the Studio view.
More on this here:
https://aximmetry.com/learn/tutorials/for-studio-operators/using-led-walls-for-virtual-production/#specifying-the-led-wall-positions 

Warmest regards,



 
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TELMIC
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Thank you for your reply.

We have some weird shaking going on in VIVE Tracker and we'll fix that.

However, I know that the Transform, Size, and Resolution of the LED wall are entered with correct values.


Do you have a sample video output correctly?

If possible, I would like to check the inside of the data as well.

I would appreciate it if you could check the studio environment as well.

Please consider it.

 
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Eifert@Aximmetry
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Hi TELMIC,

You want a sample video of how studio view looks like if the Led Walls set perfectly?:

And which data do you want to check?
Maybe later we can put together such a video, but I can not promise anything.
If you can record a video with your studio view and share data related it, that should be even better as I might be able to point out problems with it.

What said here should be enough: https://aximmetry.com/learn/tutorials/for-studio-operators/using-led-walls-for-virtual-production/#specifying-the-led-wall-positions note that even when you move the camera, the real world studio pattern of led wall shouldn't be misaligned with the virtual world's pattern.

Also you should make sure that the tracking works correctly before setting up the Led Wall. Do you use lens calibration or basic lens calibration of Aximmetry?

Warmest regards,

 
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TELMIC
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Thank you for your reply.

I'd love to check out a sample footage of a perfectly set up studio view.

If we can also check the data inside, it may lead to the solution of our problem.

We will send you details of our studio view and data at a later date. please wait a little bit.

We use Camera Calibrator to calibrate.


Please consider the sample video.

 
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TELMIC
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hello.

I have attached the captured data.


https://drive.google.com/drive/folders/1NhC8y1BwtXKVQxPRmk-aAIF4tWVZ1YZn?usp=sharing


There is a slight misalignment on the edge of the LEDwall...

Is this due to inaccurate calibration?


There is a strange movement on the edge of the image when the edge of the camera and the edge of the LEDwall are close together. Can this be fixed? Or is it like this?

 
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Eifert@Aximmetry
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Hi TELMIC,

The misalignment is quite big. It is possible to do much better with Vive.

It is either the tracking calibration is wrong or the Led Wall is wrongly placed:
Note, all of these stats above should be the same as the real-world dimensions and position of your Led Wall.

You can test the calibration in the Camera Calibrator:

Once in Test Calibration, you should look down with your camera and rotate it. The virtual floor with the numbers should stay in one place compared to the real world floor.

Warmest regards,

 
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TELMIC
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Thank you for your reply.

I have measured the dimensions and position of the LEDwall accurately, so I think the cause is probably calibration.

We have calibrated many times, but we have not been able to get better results than this video.

Do you have any tips for improving the accuracy of calibration?


I have one more question.

When I pan/tilt the camera and shake it to the outside of the LEDwall, the edge of the LEDwall moves strangely. Is there a way to fix this?

If the boundary is blurred, will this be the result?

https://drive.google.com/drive/folders/1PswzWNoZ-Xkf7IvBT9t7p9WRLhhyrBxp?usp=sharing



 
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Eifert@Aximmetry
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Hi,

The strange movement is because the Led Wall is not there in the virtual world as in the real world. The Digital Extension puts the rendered video around the Led Wall based on the virtual world position, while the video of the Led Wall comes from the real world.

Did you try the Test Calibration option? If you can make a video while you rotate your camera looking down, we can tell if it is a correct calculation or not. Even in your capture_0001.mp4 video, I can see that the virtual floor is going away from the real world floor. That is not related to the Led Wall's position. So it is likely that the tracking calibration is not accurate enough or the tracking system is not accurate enough.

Warmest regards,

 
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TELMIC
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Thank you for your reply.

We will strive to improve the accuracy of calibration.

Should I use both BasicCalibration and CameraCalibration? Do you want to use one or the other?



 
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Eifert@Aximmetry
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Hi,

The Camera Calibration program does everything you need for this.

You only need to use Basic Calibration if you want to map the Focus distances of your focus encoder. If you have a focus encoder.

If you are using Vive Mars, you can do a trick with the recentering:

You place a 2nd Rover at your led wall's center and use that Rover in the recentering:

This way, you will have a much easier time setting up the Led Walls position. Especially if you place the rover in an accurate perpendicular position compared to the center of the Led Wall.
Of course, this will only work if the rover is still in the range of your Vive Base Stations.

Also, the Rover has some centimeters of height, it is suggested you add this height to your cameras Delta Cam Transf:

Otherwise, you will have to offset everything else including the Led Wall by this height.

Warmest regards,

 
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TELMIC
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Thank you for your reply.

Is VIVE Mars more accurate? We don't have it, so if it improves accuracy, we will consider purchasing it.


 
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Eifert@Aximmetry
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Hi,

We have no information on how much more accurate is Vive Mars. Also, we don't want to give such comparisons between hardware.
You could ask Vive about that, and how it compares to your current Vive VR setup. They have contact options at the bottom of their page: https://mars.vive.com/

Also, note that in led wall productions you want to minimize tracking latency as much as you can. So that the picture on the led wall is rendered according to the latest position of your camera's perspective.
Vive Mars comes with Genlock and they say it has robust wiring to minimize latency. The Vive VR setup doesn't have Genlock and the additional hardware and program that Vive VR needs probably adds to the latency.

Warmest regards,