3-D Review

3-D Review
After SynthEyes has solved your scene, you’ll want to check out the paths in 3-D, and see what an inserted object looks like. SynthEyes offers several ways to do this: traditional fixed 3-D views, including a Quad orthogonal isometric view, camera-view overlays, user-controlled 3-D perspective window, preview movies, and velocity vs time curves.
Quad View
If you are not already in Quad view, switch to it now on the toolbar: . You will see the camera/object path and 3-D tracker locations in each view. You can zoom and pan around using the middle mouse button and scroll wheel. You can scrub or play the shot back in real-time (in sections, if there is insufficient RAM). See the View menu for playback rate settings.
Camera View Overlay
To see how an inserted object will look, switch to the 3-D control panel . Turn on the Create tool  (magic wand). Select one of the built-in mesh types, such as Box or Pyramid. Click and drag in a viewport to drag out an object. Often, two drags will be required, to set first the position and breadth, then a second drag to set the height or overall scale. A good coordinate-system setup will make it easy to place objects. To adjust object size after creating it, switch to the scaling tool . Dragging in the viewport, or using the bottommost spinner, will adjust overall object size. Or, adjust one of the three spinners for each coordinate axis size.
When you are tracking an object and wish to attach a test object onto it (horns onto a head, say), switch the coordinate system button on the 3-D Panel from to .
Note: the camera-view overlay is quick and dirty, not anti-aliased like the final render in your animation package will be (it has “jaggies”), so the overlay appears to have more jitter than it will then. You can sometimes get a better idea by zooming in on the shot and overlay as it plays back (use Pan-To-Follow).
Shortly, we’ll show how to use the Perspective window to navigate around in 3-D, and even render an antialiased preview movie.
Checking Tracker Coordinates
If SynthEyes finds any trackers that are further than 1000 times the world size from the origin, it will not save them as “solved.” You can use the Script menu's Select By Type script to locate and select Unsolved trackers. You can change them to Zero-weighted to see where they might fall in 3-D, and prevent them from affecting future solves.
Frequently these trackers should either distant horizon points that should be changed to Far, corrected, or deleted if they are on a moving object or the result of some image artifact. Such points can also arise when a tracker is visible for only a short time when the camera is not moving. The Clean up trackers dialog can do this automatically.
Note: the too-far-away test can cause trouble if you have a small world size setting but are using measured GPS coordinates. You should offset the scene towards the origin using the Shift Constraints script.
You should also look for trackers that are behind the camera, which can occur on points that should be labeled Far, or when the tracking data is incorrect or insufficient for a meaningful answer.
After repairing, deleting, or changing too-far-away or behind-camera trackers, you should use the Refine mode on the Solver panel  to update the solution, or solve it from scratch. Eliminating such trackers will frequently provide major improvements in scene geometry.
Checking Tracker Error Curves
After solving, the tracker 3-D error channel will be available in the graph editor . It is important to understand the 3-D error: it is the distance, in pixels, on each frame, between the tracker's 2-D position, and the position in the image of the solved 3-D tracker position. Let's work this through. The solver looks at the whole 2-D history of a tracker to arrive at a location such as X=3.2, Y=4.5, Z=0.1 for that tracker. On each frame, knowing the camera's position and field of view, we can predict where the tracker should be, if it really is at the calculated XYZ. That's the position at which the yellow X is displayed in the camera view after solving. The 3-D error is the distance between where the tracker actually is, and the yellow X where it should be. If the tracking is good, the distance is small, but if the tracking has a problem, the tracker is away from where it should be, and the 3-D error is larger. Obviously, given this definition, there's no 3-D error display until after the scene has been solved.
You should check these error curves using the fundamentals described earlier in Pre-Solve Tracker Checking, but looking at the Error channel. Here we’ve used isolate mode  to locate a rather large spike in the blue error curve of one of the trackers of a shot.
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This glitch was easy to pick out—so large the U and V velocities had to be moved out of the way to keep them clearly visible. The deglitch tool  easily fixes it.
You can look at the overall error for a tracker from the Coordinate System panel . This is easiest after setting the main menu's View/Sort by Error, unselecting all the trackers (control/command-D), then clicking the down arrow on your keyboard to sequence through the trackers from worst towards best. In addition to the curves in the graph editor, you can see the numeric error at the bottom of the tracker panel : both the total error, and the error on the current frame. You can watch the current error update as you move the tracker, or set it to zero with the Exact button.
For comparison, following is a tracker graph that has a fairly large error; it tracks a very low contrast feature with a faint moving highlight and changing geometry during its lifespan. It never has a very large peak error or velocity, but maintains a high error level during much of its lifespan, with some clearly visible trends indicating the systematic errors it represents.
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And finally, a decent tracker with a typical error level:
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The vertical scale is the same in these last three graphs. (Note that in the 3rd one, the current time is to the left, before frame 160 or so, hence the blue arrow.)
You can sort the trackers within the graph editor's Active Trackers node by changing Sort Alphabetic  to Sort By Error .
Do not blindly correct apparent tracking errors. A spike suggesting a tracking error might actually be due to a larger error on a different tracker that has grossly thrown off the camera position, so look around.
Check for a Smooth Camera Path
You should also check that the camera or object path is satisfactorily smooth, using the camera nodes in the graph editor. We’ve closed the Active Trackers node, and exposed the Camera & Objects node and the Camera01 node within it. We’re looking at subset of the velocities of the camera: the X, Y, and Z translation velocities.
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There's a spike around frame 215-220, to find it, expose the Active Trackers, select them all (control/command-A), and use Isolate mode  around that range of frames. The result:
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We’ve found the tracker that causes the spike, and can use the deglitch tool , or switch back to the tracker control panel  and camera viewport, unlock the tracker, correct it, then re-lock it.
Tip: In the capture above, the selected tracker is not visible in the hierarchy view. You can see where it is in the scroll bar, though—it is located at the white spot inside the hierarchy view's scroll bar. Clicking at that spot on the scroll bar will pan the hierarchy view to show that selected tracker.
If that is the last glitch to be fixed, switch to the Solve control panel , and re-solve the scene using Refine mode.
You can also use the Finalize tool  on the tracker control panel to smooth one or more trackers, though significant smoothing can cause sliding. If your trackers are very noisy, check whether film grain or compression artifacts are at fault, which can be addressed by image-preprocessor blur, verify that the interlace setting is correct, or see if you should fine-tune the trackers.
Alternatively, you can fix glitches in the object path by using the deglitch tool  directly on the camera or moving object's curves, because it works on any changeable channel. You can also move the object using the 3-D viewports and the tools on the 3-D control panel , by repositioning the object on the offending frame.
Warning #1: If you fix the camera path, instead of the tracker data, then later re-solve the scene, corrections made to the camera path will be lost, and have to be repeated. It is always better to fix the cause of a problem, not the result.
If you have worked on the trackers to reduce jitter, but still need a smoother path (after checking in your animation package), you can turn up the Filter Size control on the Solver panel. A filter size of 2 or 3 should make substantial reductions in jitter. After adjusting the control, switch to Refine mode and hit Go! again to apply the filtering.
Warning #2: filtering the path this way increases the real error, and causes sliding. Remember that your objective is to produce a clean insert in the image, not produce an artificially smooth camera trajectory that works poorly.

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最終更新:2009年03月29日 15:24
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