Object Tracking

Object Tracking

訳者注）　本文のチュートリアルよりも動画のWEBチュートリアルの方がわかりやすいです。

WEBチュートリアルwww.ssontech.com/content/fridge.htmの解説は手動トラッキングを用いているが

オートマチックトラッキングの結果（カメラトラッキング）からオブジェクトトラッキングにチェンジする方法がある。

こちらですwww.ssontech.com/content/chgtoobj.htm

カメラモードでトラッキング解析済みデータ（カメラトラッキング）から 
　shot→AddMovingObject
　shot→camera01
　Edit→SelectAll
　CoordinateSystemPanelでcamera01→objectに変更
　SolvePanelでRefine→Automaticにしてから×（cameraパス消える）
（カメラパスを削除する時、オートマチックを選んで×しないと 元のカメラトラッキングデータが残ってしまう。 ）
で、Disabledに変更してからGO を押下

オブジェクトトラッキング状態でも座標位置は設定可能なので
最初のフレームで3次元座標を設定しておく。

（以下は3ｄｓMAXの場合の手順）

この座標位置はエクスポートしたMAXへ引き継がれる。
ただしオブジェクトを置く時はworldじゃなくobject表示で設置すること。

MAX側へ取り込むと今度はカメラが固定でオブジェクトが動いている状態なので
新たに作った自分のCGへ基点（object1）のアニメーションデータをコピーしてやる。

FILE→アニメーションの合成→ソースオブジェクト選択（コピー元）→右へドラッグして作成したポリゴンへ挿入→アニメーションの合成 

ただし、MAX上でのモデリングや位置調整はカメラトラッキング状態の方が圧倒的に楽です。
なにしろ座標変わりませんから。
カメラトラッキング版で形状等を調整したモデリングを作成しておいて
MAXからエクスポートしたオブジェクトをSynthEyes側へインポートして位置合わせして

再度オブジェクトトラッキングでMAX側へエクスポートするワークフローが賢いかもしれないですね。。。 
ちなみに下記ではBOXオブジェクトを用いてマッチさせる方法を示しています。

www.ssontech.com/content/boxmatch.htm

こんな感じのことができます。

http://www.youtube.com/watch?v=QzruWH2nsNA&feature=channel_page

http://www.youtube.com/watch?v=liQXhexIYRk&feature=channel_page

 

 

Here's how to do an object-tracking shot, using the example shotlazysue.avi, which shows a revolving kitchen storage tray spinning (called a Lazy Susan in the U.S. for some reason). This shot provides a number of educational opportunities. It can be tracked either automatically or under manual supervision, so both will be described.

The basic point of object tracking is that the shot contains an object whose motion is to be determined so that effects can be added. The camera might also be moving; that motion might also be determined if possible, or the object's motion can be determined with respect to the moving camera, without concern for the camera's actual motion.

The object being tracked must exhibit perspective effects during the shot. If the object occupies only a small portion of the image, this will be unlikely. A film or HD source will help provide enough accuracy for perspective shifts to be detected.

For object-tracking, all the features being tracked must remain rigidly positioned with respect to one another. For example, if a head is to be tracked, feature points must be selected that are away from the mouth or eyes, which move with respect to one another. If the expression of a face is to be tracked for character animation, see the section onMotion Capture.

Moving-object tracking is substantially simpler than motion capture, and requires only a single shot and no special on-set preparation during shooting.

Automatic Tracking

·        Open the lazysue.avi shot, using the default settings.

·        On the Solver panel, set the camera's solving mode toDisabled.

·        On the Shot menu, selectAdd Moving Object. You will see the object at the origin as a diamond-shaped null object.

·        Switch to the Roto panel, with the camera viewport selected.

·        Scrub through the shot to familiarize yourself with it, then rewind back to the beginning.

·        Click the create-spline (magic wand) button on the Roto panel.

·        Click roughly in the center of the image to establish the center point.

·        Click counterclockwise about the moving region of the shot, inset somewhat from the stationary portion of the cabinetry and inset from the bottom edge of the tray. Right-click after the last point. [The shape is shown below.]

·        Click the create-spline (magic wand) button again to turn it off.

·        Double-click the vertices as necessary to change them to corners.

·        In the spline list on the Roto panel, select Spline1 and hit the delete key.

·        On the object setting underneath the spline list, change the object setting from Garbage to Object01. Your screen should look something like this:

·        Go to the Feature Panel.

·        Change the Motion Profile toGentle Motion.

·        HitBlips all frames.

·        HitPeel All.

·        Go to the end of the shot.

·        Verify that the five dots on the flat floor of the lazy susan have associated trackers: a green diamond on them.

·        If you need to add a tracker to a tracking mark, turn on the Peel button on the Feature panel. Scrub around to locate a long track on each untracked spot, then click on the small blip to convert it to a tracker. Turn off Peel mode when you are done.

·        Switch to the Coordinate System Panel.

·        Go to frame 65.

·        Change the tracker on the “floor” that is closest to the central axis to be the origin.

·        Set the front center floor tracker to be a Lock Point, locked to 10,0,0.

·        Set the front right tracker toXY Plane(or XZ plane for a Y-Up axis mode).

·        Switch to the Solver Panel.

·        Make sure the Constrain checkbox is off.

·        Hit Go!.

·        Go to theAfter Trackingsection, below.

Supervised Tracking

The shot is best tracked backwards: the trackers can start from the easiest spots, and get tracked as long as possible into the more difficult portion at the beginning of the shot. Tracking backwards is suggested for features that are coming towards the camera, for example, shots from a vehicle.

·        Open the lazysue.avi shot, using the default settings.

·        On the Solver panel, set the camera's solving mode toDisabled.

·        On the shots menu, selectAdd Moving Object. You will see the object at the origin as a diamond-shaped null object.

·        On the Tracker panel, turn onCreate. The trackers will be associated with the moving object, not the camera.

·        Switch to the Camera viewport, to bring the image full frame.

·        Click theTo End button on the play bar.

·        Click the Playback direction button from to (backwards).

·        Create a tracker on one of the dots on the shelf. Decrease the tracker size to approximately 0.015, and increase the horizontal search size to 0.03.

·        Create a tracker on each spot on the shelf. Track each as far as possible back to the beginning of the shot. Use the tracker interior view to scroll through the frames and reposition as needed. As the spots go into the shadow, you can continue to track them, using the tracker gain spinner. When a tracker becomes untrackable, turn off Enable, and Lock the tracker. Right-click the spinner to reset it for the next tracker.

·        Continue adding trackers from the end of the shot roughly as follows:

·        Begin tracking from the beginning, by rewinding, changing the playback direction to forward, then adding additional trackers. You will need to add these additional trackers to achieve coverage early in the shot, when the primary region of interest is still blocked by the large storage container.

·        Switch to the graph editor in graph mode, sort by error mode. Use the mouse to sweep through and select the different trackers. Or, select Sort by error on the main View menu, and use the up and down arrows on the keyboard to sequence through the trackers. Look for spikes in the tracker velocity curves (solid red and green). Switch back to the camera view as needed for remedial work.

·        Switch to the Coordinate System control panel and camera viewport, at the end of the shot.

·        Select the tracker at center back on the surface of the shelf; change it to anOriginlock.

·        Select the tracker a bottom left on the shelf, change it toLock Pointwith coordinate X=10.

·        Select the tracker at front right; change it to anOn XY Planelock (or On XZ if you use Y-axis up for Maya or Lightwave).

·        Switch to the Solver control Panel.

·        Switch to the Quad view; zoom back out on the Camera viewport.

·        Hit Go! After solving completes in a few seconds, hit OK.

·        Continue to theAfter Trackingsection, below.

After Tracking

·        Switch to the 3-D Objects panel, with the Quad viewport layout selected.

·        Click theWorldbutton, changing it toObject.

·        Turn on the Magic Wand tool and select the Cone object.

·        In the top view, draw a cone in the top-right quadrant, just above and right of the diamond-shaped object marker.

·        Hint: it can be easier to adjust the cone's position in the Perspective view, locked to the camera, withView/Local coordinate handlesturned on.

·        Scrub the timeline to see the inserted cone. In your animation package, a small amount of camera-mapped stand-in geometry would be used to make the large container occlude the inserted cone and reveal correctly as the shelf spins.

·        Advanced techniques: useCoalesce TrackersandClean Up Trackers.

Difficult Situations

When an object occupies only a relatively small portion of the frame, there are few trackers, and/or the object is moving so that trackers get out of view often, object tracking can be difficult. You may wind up creating a situation where the mathematically best solution does not correspond to reality, but to some impossible tracker or camera configuration. It is an example of the old adage,“Garbage In, Garbage Out”(please don’t be offended, gentle reader).

Goosing the Solver

Small changes in the initial configuration may allow the solver to, essentially randomly, pick a more favorable solution. Be sure to use theSlow but surecheckbox and all the different possibilities of the Rough camera motion selection, both on the solver panel. Trying a variety of manually-selected seed frames is also suggested. Small changes in trackers, or adding additional trackers, especially those at different depths, may also be helpful in obtaining the desired solution.

Inverting Perspective

Sometimes, in a low-perspective object track, you may see a situation where the object model and motion seem almost correct, except that some things that are too far away are too close, and the object rotates the wrong way. This is a result of low/no/conflicting perspective information. If you cannot improve the trackers or convince the solver to arbitrarily pick a different solution, read on.

TheInvert Perspectivescript on the Script menu will invert the object and hopefully allow you to recover from this situation quickly. It flips the solved trackers about their center of gravity, on the current frame, changes them to seed trackers (this will mess up any coordinate system), and changes the solving mode toFrom Seed Points. You can then re-solve the scene with this solution, and hopefully get an updated, and better, path and object points. You should then switch back to Refine mode for further tracking work!

Using a 3-D Model

You might also encounter situations where you have a 3-D model of the object to be tracked. If SynthEyes knows the 3-D coordinates of each tracker, or at least 6-10 of them, it will be much easier to get a successful 3-D track. You can import the 3-D model into SynthEyes, then use the Perspective window's Place mode to locate the seed point of each tracker on the mesh at the correct location. Turn on the Seed checkbox on for each, and switch to the From Seed Points solving mode on.

If you have determined the 3-D coordinates of your tracker externally (such as from a survey or animation package), construct asmall text filecontaining the x, y, and z coordinates, followed by the tracker name. Use File/Import/Tracker Locations to set these coordinates as the seed locations, then use the From Seed Points solver option. If the tracker named doesn’t exist, it will be created (using the defaults from the Tracker Panel, if open), so you can import your particular points first, and track them second, if desired, though tracking first is usually easier.

The seed points will help SynthEyes select the desired (though suboptimal) starting configuration. In extreme situations, you may want to lock the trackers to these coordinates, which can be achieved easily by setting all the imported trackers to Lock Points on the Coordinate System panel. To make this easy, all the affected trackers are selected after an Import/Tracker Locations operation.