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Tracking Drone footage
Posted: 14 August 2017 11:25 PM   [ Ignore ]  
Total Posts:  6
Joined  2015-10-11

Hi,
This is actually my 2nd post about the same topic. I’ve been tracking lots of footage for a client using c4d and all is going well except this one piece. For some reason when I go to add my planar constraint to tell the motion tracker the “Y” axis I am getting some strange results. This is the process I’m following:

1. Load footage - 25fps (have been using image sequences but for the example am using an mp4 as its smaller)
2. Number of tracks: 1500, auto-track from the middle of the timeline
3. Reduce error threshold down to 10% (delete any wobbly tracks)
4. Then Full 3D Reconstruct (camera is 24mm focal length from camera operator)
5. Add position constraint for world axis
6. Add vector constraint and set to “Z” plus attach to my chosen tracks
7. Add planar constraint and set to “Y” and attach to my chosen points

Its at the last stage my planar constraint doesnt want to point to the Y not mater which track points I attach it too.

I’ll include my scene file too if anyones knows what I’m doing wrong, the zip contains my footage as well…

https://spaces.hightail.com/receive/iQO49LxThp

Any suggestions is very appreciated as I’ve been trying to track it for quite a few hours now.
Cheers,
Jody

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Posted: 15 August 2017 12:31 AM   [ Ignore ]   [ # 1 ]  
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Hi Jody,

This is solvable. Let me guide you through the problems and the specific solution to this one.

The first thing that comes to mind is, that it is pretty much a “locked-off” shot. There is very little movement, just rotation. In order to have a good solve on the tracking features, one needs to have more parallax. If the Drone had some substantial movement before it stopped and took the “panorama” in the same clip, that would be more helpful to solve it in one take.

What the tracking can do, is to give you an good idea about the rotation of the camera, but the movement is too little, hence your problems. Edit: the movement is only based on bad trackers, the drone was based on my new tracking pretty much locked off). Let’s have a look first to the problems and then how to solve them.

If you go to the side view of your file, you can see how much vertical difference the tracking points show, but the landscape seems pretty flat. If this would be more flat, I would suggest to use more points than three. As shown here
https://www.cineversity.com/vidplaylist/motion_tracking_object_tracking_inside_cinema_4d/motion_tracking_object_tracking_inside_cinema_4d_tracking_the_main_shot
at 03:45 min:sec
Think of the a stabile and easy to draw triangle, that would be one with nearly equal sides. One side stands for the movement of the drone, as mentioned the parallax. IF there is no or very little movement, one side of the triangle is very small, and the point in opposite of the small movement, is not very precise. Think of an idea 90º crossing of two lines, that is pretty precise. Then draw two line with 3º crossing each other, the crossing point is much harder to tell. The typical tracking point cloud of a lock off shot looks more like a sphere, not flat at all, hence your problems to orientate it. It wont.

How to get a good solve anyway? I would suggest to take one image from the footage and use the Camera Calibrator. I have taken the first image and placed the needed parts into the scene. Since I don’t know where that is, I had to guess and assume that something is in an 90º relation. You can check with Google Maps/satellite perhaps more points.


Scene file
https://www.amazon.com/clouddrive/share/e8d0IqsffLbIuNaD9xBZZPEpuSRAydCx1SL31klq3jD
Note that I do not have any set-survey from that area, you have certainly more data.Based on that, I did not matched it to your scene.
The middle part of the clip might be even better…

This gives you an idea how the camera is oriented if the assumption that the floor is leveled and flat is kind of right. This relationship of camera and ground for that image. Create a Null.0, a new Null— never use a “Group Command” for animation, ever. Place all your parts under Null.0. Then create another Null.1 and move this Null.1 to the camera, so they have the same position. Now move the first Null.0 under the newer Null.1.
This top Null.1 can be now moved to orient your camera. The Calibrated Still image version can be now used as guide to adjust the motion camera with that top Null.1. Not that the distance to the floor object is different, this doesn’t matter for now, as all we want is the motion camera to start with a view to a leveled floor (my assumption it is flat and leveled).

Now place a flat polygon on the floor, somewhere in the tracking feature cloud, and move the time slider. If it slides move the plane up or down. Sounds not very precise, and it works only to a certain degree. better is, to have in both scene the same feature, like a axis/vector with the same length, so both scene match already.

This should get you very close.

The lens with 24mm equivalent of 35mm film sounds pretty much like the Phantom4 Pro, with a 4K crop of its 20MP sensor which should be then more like 32mm, but I’m guessing here, and that is not a good way to solve, some people use real 4K some UHD, etc. What I miss here is a lens chart, so you can crate an lens-profile, which will increase the precision.

“Wobbely”, I’m not certain what you have exactly in mind with that. If it is rolling shutter, that will not be eliminated by changing the tolerance value, as it is an partial image problem. Cinema 4D has no option for that.

When you track, the closer the points to the camera, the more precise they are. Point far away from the camera will get less and less precise. I even delete far away points most of the time, to just have no headache at all about them.

If you can redo the shot, have a straight fly to, like a dolly for as much length as possible, then stop, and have your pano. Take a lens calibration image from that camera and lens. Syntheyes has one for download, it can be printed out largely as “letter” pdf instead of a large image print. I paid for mine not even $10, three feet wide. You can’t take from any other drone the calibration, as these lenses are not super precisely centered.

I hope that will help you to fix the problem.

All the best

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Dr. Sassi V. Sassmannshausen Ph.D.
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Posted: 15 August 2017 02:48 AM   [ Ignore ]   [ # 2 ]  
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P.S.: Please have a look at this file. I did exactly as I have described it above. To be more precise, I placed Null.1 under the Still Camera Camera + Camera Calibration, and used the Character>Commands>Reset PSR, then I moved the Null.1 with all the child objects away from it.

Yes, I tracked the whole scene newly. What I might did differently, I started to “Create Automatic Tracks” at frame zero, then <Auto Track>.
Last frame, again “Create Automatic Tracks” then <Auto Track>.
Then a frame in the middle of the timeline (half roughly…)  again “Create Automatic Tracks” then <Auto Track>.
At a quarter of the time line “Create Automatic Tracks” then <Auto Track>. Again at 3/4 of the timeline Last frame, again “Create Automatic Tracks” then <Auto Track>.

This gave me a nice dense option for the tracking. I do that pretty much every time, BTW.

The solve of the 2D tracker in the reconstruction showed me that the Drone was pretty stable. But any “rotation only” will create tracking features like a sphere around the rotating camera, as there is no parallax.
To gain that information I used the Calibrated camera with the still image from frame zero.

All footage or the still is not included in the file, as you have it already.

Scene file
https://www.amazon.com/clouddrive/share/COEWOmLy8lt16hARV3DVx0Hwkc7jd7GFgN1l3jSA2ob

I used my lens profile, again - not suggested, but better this, if it was a DJI 4pro, than none at all.

Any slide that you see, starts at the edge/frame of the image, as the footage is distorted, but the C4D content is not. This is normally fixed in post, or doing rendering with the right lens profile.

This is certainly not 100% but certainly pretty close wink
Preview Clip:
https://www.amazon.com/clouddrive/share/a2cJbwfbEyhieZymTUZBrtMJ6BR8ctVxO28dCBLl1m

My best wishes

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
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Posted: 15 August 2017 05:23 AM   [ Ignore ]   [ # 3 ]  
Total Posts:  6
Joined  2015-10-11

Thanks Dr. Sassi for your reply, I’ll download your sample files and read through your explanations. Gosh your answers are always so thorough!  Will post a followup with how I go, I hope somebody else finds this info usefull as well when it comes to tracking drone footage.
Cheers,
Jody

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Posted: 15 August 2017 02:56 PM   [ Ignore ]   [ # 4 ]  
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You’re very welcome, Jody.

Yes I go through the details, so it solves the problem on the long run, not just for now. At least that is my hope.

I know that some people want only a “fix it for me”, but that keeps them dependent, which Isn’t my target.

Please let me know if there are any questions, since this is kind of a special case and each step might count a little bit more than usual.

To give the non detail super short version here:
A single frame is picked out and solved as still image (Camera Calibrator). This is then used for the “Pan-Shot” to establish the wanted relation to the flat floor.

Enjoy your project.

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
https://www.youtube.com/user/DrSassiLA/playlists

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