I have constrained a camera to track to an empty, and I've constrained the empty to limit its distance from the camera to outside 5 m and inside 10 m. I have parented the camera with the track-to constraint to another camera with a follow-path constraint.

The parent camera was used to set up the path by flying it to find good shots and placing empties there, creating a single vertex at the first empty, extruding to each succeeding empty, converting the line to a curve, changing spline type to bezier, smoothing and refining. Then the parent camera was constrained to the path and the path was animated. The timeline was scrubbed to move the camera to each empty on the path, the camera constrained to track was made the active camera, and from camera view the tracked empty was moved to align the view with the desired shot. The location of the tracked empty was then keyframed.

This workflow works nicely for me except for a couple of glitches. These could be solved by creating a path through the locations where the tracked empty was keyframed and using that to direct the rotation of the camera, but that involves a lot of extra steps,and a lot of these shots need to be set up. I hoped that somehow refining the constraints would yield a better solution, but I'm not very familiar with constraints and don't know if that is possible.

First, because the empty can't come closer than 5 m from the camera, it gets dragged by it in a way that occasionally causes problems - it doesn't move on a straight line between keyframe points. It chooses a path that keeps it 5 m from the camera, even though it is allowed to be up to 10 m from the camera, and if it combined those rules it could move in a straight line between points. Second, I mistakenly set up a situation that would oblige the empty to come too close to the camera, and even though I corrected that by replacing the keyframes, the empty still veers wildly between the keyframe points involved, like it remembers the path that was previously calculated to satisfy the limit distance constraint. In fact I can't make it move further than 5 m from the camera, it acts as though it is supposed to stay exactly 5 m away.

When there is no Limit Distance constraints on the tracking empty, lining up shots by using it breaks after a short time. The shots are lined up while in camera view. Moving the empty from this perspective causes it to converge on the camera after a short time and then it is uncontrollable.

But getting the camera to behave properly is very slow and difficult any other way. If it looks at an empty on a path, the movement of the empty on the path has to be offset repeatedly to get the desired effect. It's very hard to get that right, especially if the path of the camera and the path between pause points of the empty is complex. If the rotation of the camera is keyframed, it's very hard to get it to focus on something for any length of time as it moves. I have done the kind of architectural flythrough video I'm working on now before. I've spent a day and a half trying to set up an empty on a path to behave as desired only to accept a mediocre result because I was out of time.

Here is an illustration of the problem behaviour at the moment. Note that the system works very well until this end bit.

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Here is the console window provided by a reader of the question.

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Is there a way to tweak these constraints to eliminate these problems?

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  • Actually, i could be completely wrong about why the empty is dipping down and then veering wildly. That's another possibility. But i'd like it to not do that. – kim holder Oct 10 at 16:19
  • I do not understand the question completely. I do have a question. When you open the console window do you see any warning messages? – atomicbezierslinger Oct 10 at 16:26
  • It would also be useful to see the screen capture of you constraints. – atomicbezierslinger Oct 10 at 16:27
  • @atomicbezierslinger No, no warnings. The limit distance constraints? – kim holder Oct 10 at 16:28
  • Please attach the contents of the console window. Menu /Window /Toggle System Console – atomicbezierslinger Oct 10 at 16:43

I am suggesting you

  • Backup and Archive your work
  • remove the cyclic dependency which means removing the limit distance constraints. This information is provided in the console window.

Alternative 01

  • place the empty on newly created path. Thus the camera is on path1 and the empty is on path2.
  • remove the limit distance constraints, repeated for emphasis
  • Please know that that changing a path changes its distance and thus keyframes on a path start moving. If you can possibly lay out the whole path for the empty at once or nearly so please try and be aware of the situation. You have many follow path constraints with ebbing flowing [influence] as scary as this seems. Sometimes the separation allows less work.

Alternative 02

  • This may or may not be an advanced technique alternative to the path constraint. There is a [copy location] constraint with [influence] which may allow a object to reside a certain point at a certain keyframe with certainty once the time and effort of setting up the arrangement of objects and keyframes is made.
  • I am in the process of trying to remove the cyclic dependency. I haven't done that before so it's trial and error. That would remove the need to do the other things though, if that then allows the system to work. It almost was. – kim holder Oct 10 at 17:06
  • Are you saying there is no way to remove the cyclic dependency and preserve the functionality as it is? – kim holder Oct 10 at 17:09
  • I am trying to convey its ill-advised to have a cyclic dependency. I see no explanation for the limit distance or its use. Please explain its use. Thus I more ready as the reader to delete that constraint. I have less sunk cost bias because I did not do your work. – atomicbezierslinger Oct 10 at 17:24
  • The empty has about 7 keyframes . I may be in error. I do not consider that to be many for rework. I have not experimented with your file because my time is limited at the moment. I have not investigated if the cyclic dependency if it is cause large or small problems or no problems. – atomicbezierslinger Oct 10 at 17:29
  • If I remove the distance constraints then the empty moves in a entirely different way. So I wont have time to know what is intended by you. I will say a fresh start can be ... – atomicbezierslinger Oct 10 at 17:52

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