How to match the spatial distance between reality and virtual?

Studio Operators Bugs Editions Camera Tracking

 

In the test of the tracking camera, I found that the moving distance of the real physical world is inconsistent with the moving distance of the virtual space, including the size of the object. Is there any way to solve it? Or are the units in virtual space meters or millimeters?

Thanks a lot.

   Rain_law

 
Profile Image
TwentyStudios
8/3/2022 9:49:07 AM
  -  

You need to calibrate your camera with the tracking system. The scene also needs to be built to a proper scale, which isn’t always the case. 

 
Profile Image
Rain_law
8/4/2022 3:44:31 PM
  -  

Hello, as you can see from these two pictures, after my tracking camera moves forward, the captured object gets bigger, but the virtual scene doesn't get bigger synchronously, I'm not sure what calibration I need to do

 
Profile Image
TwentyStudios
8/4/2022 5:21:56 PM
  -  

@Rain_law: You need to match the files of view of your real lens to the virtual lens and calculate the offset between the camera entrance pupil and your tracker. This information is just a simple google search away. Depending on what version you’re using you would use the new Camera Calibrator or the old Basic Camera Calibrator. Like I said, lots of info on this just a search away, but here’s something to get you started: https://aximmetry.com/learn/tutorials/for-studio-operators/basic-lens-calibration-without-lens-distortion/

 
Profile Image
Rain_law
8/5/2022 12:49:20 AM
  -  

@TwentyStudios Thank you for your feedback, I have also seen a lot of this method through searching, but I don't quite understand how my lens calibration can improve the effect so much.

 
Profile Image
TwentyStudios
8/5/2022 12:48:12 PM
  -  

@Rain_law: I’m not just talking about lens distortion calibration here. Think of it in terms of scale. If the field of view of your real camera and the virtual camera don’t match they’re essentially operating at different scales. So the real and virtual worlds might line up perfectly at a single position, but if you move the physical camera it will drift more and more away from the position of the virtual camera, since it’s not in the same actual scale. Does that make sense?

 
Profile Image
Rain_law
8/5/2022 3:41:52 PM
  -  

I followed the camera calibrator process today and found a few issues. The first one is that I have a zoom lens and I may change the lens later, can the calibration result be applied to other focal lengths or other lenses? Is the every changes I make to the camera needs to be recalibrated? Another one is do you use slide rails when testing? May I use stabilizers or the like? Thank you!

 
Profile Image
TwentyStudios
8/5/2022 4:09:46 PM
  -  

These are not issues, it’s just how camera tracking works. No way around it. If you have a Zoom lens you need a way to read to zoom position. Easiest way is to use a lens encoder like Indiemark. You would then use the full camera calibrator app and run the calibration across several points on the zoom range. 

If you want to change the lens you need to calibrate that lens as well and then load the calibration file for each lens every time you switch again.

Camera tracking doesn’t really care about what the camera is mounted on. It could be a slider or a gimbal, as long as the tracker is mounted on the camera so it can track all the motion. You do need to turn off all lens and in-camera stabilization of course.

I strongly recommend that you read the documentation and watch some tutorial on camera tracking to get an understanding of how everything fits together.

 
Profile Image
Rain_law
8/5/2022 5:40:32 PM
  -  

@TwentyStudios I have seen this method of Indiemark before, but I forgot it for a while, thank you for your reminder. In addition, what I just said is when doing lens calibration, is it more stable to use the slide rail? This kind of document, I haven't seen any master said so far, so I'm also very confused. So there are many temporary questions, and I am now looking for answers in the forum.

 
Profile Image
TwentyStudios
8/5/2022 5:44:22 PM
  -  

I don’t understand the question about the slide rail. What does a slider have to do with camera calibration?

There are lots of information on camera tracking all over the internet. Start with googling Aximmetry camera tracking. 

 
Profile Image
Rain_law
8/8/2022 10:46:01 AM
  -  

@TwentyStudios 

I have recalibrated my lens, but it still sucks, I don't know what's wrong. Below is a screenshot of my actual situation. Please take the time to see what the problem is, thank you!



 
Profile Image
Eifert@Aximmetry
8/17/2022 2:30:14 PM
  -  

Hi,

It seems that the zoom level (FoV) is different from the one in the real world. But it can be a different problem.

These cubes are 1m big and when projected on the real world, the real world should have the same size. In this picture the real world is much smaller than the virtual one:

It is actually 4 small cubes that makeup one big cube marked with red in this screenshot. On the small cubes, 2 has the same number displayed that mark the distance from the zero point in meters.

You are using an HTC Tracker which doesn't transmit zoom level. If you don't have a zoom encoder for the zoom. You have to use fixed FoV in Aximmetry's camera calibrator and after that, you can not change the zoom level.
More on Aximmetry's camera calibrator: https://aximmetry.com/learn/tutorials/for-studio-operators/camera-calibrator/

Warmest regards,

 
Profile Image
Rain_law
8/17/2022 3:43:48 PM
  -  

@Eifert@Aximmetry 

Thank you very much for your reply. After this problem, we used the calibration software to recalibrate it again. The effect has been improved, and the object tracking is also more suitable. But I can't say it's completely correct. Because my place is very limited, I used a wide-angle lens at that time, and the scene was enlarged to match the proportion. But no one told this problem before, so I missed this point during the inspection. Unfortunately, I can't send a video here to show you the effect. Of course, I still have two forum posts that need your company's help to read, and then give a reply. I still don't understand these two questions. I also read the replies on the forum, but still want to confirm the latest solution to this kind of problem. One is "the shadow of the shot object" and the other is "set a virtual object as the foreground ". Thanks!