Monorail Object Tracking
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Hi, I’m trying to track the Monorail (tracking file+footage attached).
The problem is that the footage isn’t ideal. I think the camera motion tracking is more or less okay, but the object-tracking of the monorail doesn’t really work because it isn’t consistently and fully visible.
The mesh is only there to capture some rough reflections in the end - my goal is to wrap 3D fairy lights around the train.
I’m taking care of masking etc. in After Effects; what I really need is a reasonably solid object-track of the train for the 3D fairy lights.
Maybe there are some dirty tricks to achieve this. I’ve tried simply animating the train by hand and even playing with animating the focal length, but that didn’t really work either.
Thanks in advance!
File:
https://www.icloud.com/iclouddrive/0ecdtw9TeUd1j1WmjHPwYEeaw#Cinneversity%5FObject_Tracking -
Hi Tuffi,
Thank you very much for the file!
The problem with this shot is manifold.
The Object Tracker needs first a Camera Track (as you did); otherwise, it might not really know what is going on. However, since this is from one location with little motion, hence no data in space that is reliable.
In other words, the shot is done pretty much like a lock-off shot, meaning it has no parallax change in the main part of the image.
The Footage is obviously from a phone, and there is a more complex problem. It typically has a rolling shutter, which prevents clean tracking.
On top of that, most of those shots have stabilization automatically applied, which means the image is moved inside of an overscan, and that doesn't change the perspective inside the frame, meaning it is wrong.
If all of that is in this shot, I can only assume.
Besides, there was no lens grid used in the shot, nor was the focal length set. I did not find a mask on the track to exclude the train first, to get a better result.Typically it is good to have some set-survey, while in this case, perhaps Google-Earth would work. When the camera point of view is known, at least the Focal length can be checked to a certain degree, and if the rail is straight in that section, etc.
I mentioned that not to critique your setup, but to illustrate the problem.
Please merge this example into your tracked scene.
CV4_2026_drs_25_TRws_11.c4dThe idea is simple: if the camera was tracked in its rotation correctly, while the track of the "Schwebebahn" or Monorail is pretty straight in that section, I used the part where the camera is perpendicular to the train, and placed a cube along its side. Again, this is on a nearly straight portion of the track. The idea here was to have the straight line established, and then move the cube with the train step by step, meaning every 50 frames or less.
You could define the position of the train with the Camera Calibrator for a single frame, to align the train. I used that "often" when a drone shot was used that just rotated a little bit in the air. Similar case here, except locking up instead of down.
Another idea is a little bit of a hack. A traveling mask tag (Mask Constrained is rotoscoped to get only the train. Then you track only what is inside the mask. The tracker assumes now that the train is like a building, and the camera moves as this is the only part of the whole shot that has parallax in it. Again, this is more of a hack, as the train is very small. But to get the train tracked to have an object representing it works.
My quick test is below.Yes, I re-rendered the images to get a 0-303 frame number sequence. I have the feeling that two million as a frame number is not working with my computer as the frame sequence starts.
The file is a very rough draft, quickly done. Not for production, just as a demo.
CV4_2026_drs_25_TRws_01.c4dMy best wishes for your project
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P.S.: The train is tricky, but I had to try again.
The train is partially based on object trackers, and partially on a quick RotoTo run lights around it might be enough…
https://projectfiles.maxon.net/Cineversity_Forum_Support/2025_PROJECTS_DRS/20251121_CV4_20226_drs_25_TRws_21.c4d.zip
Or another exploration
https://projectfiles.maxon.net/Cineversity_Forum_Support/2025_PROJECTS_DRS/20251121_CV4_20226_drs_25_TRws_31.c4d.zip
As mentioned, the nearly lock-off shot has problems seeing "distance".
Think of the movement of the camera, while having a target point, which will create a "V" like viewing axis of the start and end point. This allows us to calculate the distance. If these two viewing axes are on top of each other, no distance can be calculated.When I "manually roto" the train, the distance that it travels and the tracking points describing the context are in a very different world. "A full lock-off pan around the nodal point" creates in most tracking apps just a sphere." Yes, I tossed it for a test also in Syntheyes. I got a perfect pan of the camera, but that was it. To set a lot of manual tracker for teh train will surely improve the results, but I am as before concerned about phone based problems.
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Hi, thanks so much for the quick reply and all the effort.
On Saturday I went through the rotoscoping workflow with a lot of trackers and it already worked quite well. I also added a bit of animation to the mesh, and this week I’ll test whether I can achieve believable results. In the end, it’s really a learning experience for me how to handle material this challenging material. The Camera Calibrator tool is also very helpful. I’ll check out the other project files as well, thank you! -
Hi Tuffi,
You're very welcome.
Yes, that is a learning journey, thanks for sharing your impression.If your great website is any indication of where you like to go with Motion tracking, I'm sure that you will develop a great deal of knowledge. I hope you enjoy the ride.
I shared a whole pipeline about Motion Tracking here:
https://www.youtube.com/watchv=7za0ozspxIg&list=PLOLI4wu7NPsjGPK3BGKJpmAg9WqFodFHh
Part three is perhaps a timesaver clip.
This and the longer series here on Cineversity should give you a good base to grow your knowledge.
https://cineversity.maxon.net/en/series/motion_tracking_object_tracking_inside_cinema_4d?tutorial=motion_tracking_object_tracking_inside_cinema_4d_introductionPlease let me know if any question comes up. If it is a new question, please use a new "forum thread" so it is easy for anyone to search for a solution for similar problems. Thank you.
Enjoy your exploration
