Solving the camera

The tracking is done now on the camera track training clip using all default settings on the tracking tab. So we can now do the Camera Solve. This is where the camera's positions and the 3D points in the scene are calculated. After solving the camera we could then refine the tracking data and re-solve the camera to get a reduced overall tracking error. To solve the camera we just click the Solve Camera button and the Camera Tracker calculates the camera position and points from our tracking data and we're done.

To see the results we click on the Refined tab and look at the Solve Error right here. We will call it (.86). This is the RMS or Root Mean Square Solve error. Think of it as just a fancy average of all the errors. Next we'd like to delete any bogus tracks. These can come from reflections which are not a valid object or intersections between two elements in the scene. The tracker will sometimes lock onto those, so we have to tell it to drop them. We come over here and I am just going to select this red guy here, Shift+Click to select this one and then I'll do a Shift+Rectangle on these two.

I now have four yellow track selected, Right Mouse pop-up, delete selected. Now if we move down the timeline we'll find the new bad tracks enter the frame. Let's say right here. So we will select those, Shift+Click here, Shift+Click there, Right Mouse pop-up, tracks>delete selected. So we've thrown out several bogus tracks. Let's now re-solve the camera to improve the Solve Error.

We do not have to go back to the Camera Tracker tab and click on Solve Camera, because they have thoughtfully put another Solve Camera button here. This is the rule: whenever you delete tracks you must redo the Camera Solve. So I am going to click a Camera Solve, we get the little warning message, I say, yes. And now we will watch the Solve Error up here after it recalculates, .80. I have made a good improvement on myself. The minimum Solve Error you want is 1.0, but you'd like to get a .5, .5, half a pixel, is a real tight Camera Solve.

So that we'll be our target. So to the further refine the solve we will come down here into the Track Info area. This is a bunch of statistics and thresholds that have been collected by the Tracker for us. For example, num tracks is, of course, the number of tracks per frame. As you can see we had more tracks here at the beginning of a shot than we did at the end of the shot. Track length minimum is of course the minimal length of tracks on a per frame bases in the clip. If we click in the Viewer and type F, we'll scale up the Viewer.

To see the threshold do a Command +Click on the Min Length parameter. This is the threshold that rejects all tracks that are shorter than this threshold and it's controlled right here Min Length. If I move the slider up to here, for example, I am saying any tracks that have a minimum length of less than 8, I want you to ignore them in the calculations. Now when we're refining the calculations we do not do the Solve Camera, we use the Recalculate Solve button.

Solve Camera is reserved for when you delete trackers. So I am going to Recalculate the Solve, watch my Solve Error up here, and there, I got a very small improvement, but I'll take it. Now let's take a look at the error - min or minimum. Click in the Viewer and type F. All of these errors refer to the Reprojection Error. The Reprojection Error is calculated by comparing a 2D tracking point on the screen with its associated 3D point.

The smaller the error the closer they match. Now let's take a look at error - rms which would be of course the average error. Its threshold is right here Max Track Error, and I am going to click in the Viewer and type F so we can see it up here. It's so much higher than the collected data, because it was based on the old tracking data when we had some focus points which are now gone. The Max Track Error slider sets that threshold. So I am going to move this down and I'm telling it I want you to reject these bad boys here.

So now we'll Recalculate the Solve, watch my Solve Error here, Bang! .46. Very good! I made a very big improvement. Next, let's look at the error - max this of course is the maximum error per frame and its threshold here is Max Error. Click in the Viewer, type F. We can see the Max Error threshold way up here. So again, if I pull the slider down, I am telling it to ignore everybody that's above the threshold.

And one more time I will Recalculate my Solve, watch the Solve Error up here, boom! I made a small improvement, but I'll take it. We've refined our data as much as we can. We'll go back to the Camera Tracker tab and we're ready to create the scene, which will build the 3D PointCloud and the 3D Camera.