In this video we will wrap up the attributes of the motion tracker object by looking at the reconstruction tab. Here you define parameters relating to the 3D solve. For any of this to make sense, you need to have a good 2D track. The reconstruction sub-tab allows for selecting the solver algorithm. We will only use a default full 3D reconstruction in this series. Underneath that is where we set the focal length parameters for the tracked camera. The little menu has three options for focal length. The default, Unknown but Constant, means you have no clue what the focal length is, but you know for a fact that no zooming occurred during the shot. For your information, when you zoom in or out, you're actually changing focal length. The larger the focal length, the more the zoom, and vice versa. When using this setting, the camera lens focal length and sensor size will be calculated automatically by the tracker, and applied to the solved camera after the 3D solve has finished. So I repeat, for fixed lenses, or if you know that there was no focal length change, this is what you must select. Moving on, unknown means no clue whatsoever, which means that either there is zooming, or you can't be sure. If the footage to track was given to you, and no other information is available, my advice is to go through the footage and try to estimate if any zoom is occurring, then decide which setting to use. The last setting, Known and Constant, is what you select if you know, or have estimated, the focal length. Just so that you know, minor deviations from the actual focal length value will not impact the 3D solve too much, but it's better to be as accurate as possible. The grand Run 3D Solver button at the bottom is it. Press that, and the 3D solve will commence. After the 3D solve has completed, each 2D tracker gets a null assigned to its respective three dimensional position. Don't forget, although trackers represent two dimensional positions themselves, they correspond to a 3D position. That's what this whole tutorial is about, after all, transforming a bunch of 2D data into 3D. With the display settings, we just define the shape and size of these nulls. Each null will inherit the error color of its respective 2D tracker. Green is good, and red is, oh, well, not so good. There is a small setting I left for last. It's the Lock Solved Data, and it's very important. Here's when you should activate it. A 3D solve relies 100% on the 2D tracks you have created, the specific 2D tracks, and any camera parameters you have used. If any of the previous things changes, even a single tracker, then the whole 3D solve is invalid, and will have to be deleted and recalculated if you press Run 3D Solve again. Now the object tracking workflow can be done after the camera tracking, and actually, that's what I will teach you to do. But that entails that you will add some new trackers to the shot, the ones you'll track the object with. So this setting instructs the tracker to keep the solve data, camera, nulls, and all, regardless of the changes you'll do. So after you're happy with the 3D solve, activate it to avoid any unnecessary data loss before you start tracking the object trackers. So this concludes our overview of the motion tracker object attributes. Let's move on to the object tracker now.