Getting Started

When you first open Tracker it appears as shown below. Here's how to start analyzing a video:

1. Open a video or tracker file.
2. Identify the frames ("video clip") you wish to analyze.
3. Calibrate the video scale.
4. Set the reference frame origin and angle.
5. Track objects of interest with the mouse.
6. Plot and analyze the tracks.
7. Save your work in a tracker file.
8. Export track data to a spreadsheet.
9. Print or copy/paste images for reports.

For more information about Tracker's user interface, including user customization, see user interface.

1. Open a video or tracker file

Click the Open button or File|Open menu item and select a QuickTime video (.mov) or tracker file (.trk) to open it. Other video types can be opened as long as QuickTime can play them. You can also open image files (.jpg, .gif, .png) or paste an image from the clipboard. For more information see videos.

2. Identify the frames ("video clip") you wish to analyze

Display the clip settings by clicking the clip settings button at the right end of the player as shown.

In the clip settings dialog, set the Start and End frames to define the range you wish to analyze. You can drag the player's slider to scan through the video and quickly find the frames of interest. If the video contains too many frames to analyze (more than 20 or so can become tedious), increase the Step Size to automatically skip frames. For more information see video clips.

3. Calibrate the scale

Click the Tape Measure button to show the tape measure.

Drag the two ends of the tape to positions that are a known world distance apart (for example, the ends of a meter stick or other object with known dimensions in the video image). Then click the tape readout and enter the known distance. For example, in the figure below the scale is set in cm units using a white meter stick with black stripes every 10 cm.

For more information see tape measure, or for an alternate way to calibrate the video consider a calibration point pair.

4. Set the reference frame origin and angle

Click the Axes button to show the coordinate axes. Drag the origin and/or x-axis to set the reference frame origin and angle. A common choice for the origin is the initial position of an object of interest. For more information see axes, or for alternate ways to set the origin and/or angle consider the tape measure, a calibration point pair or an offset origin.

The video scale and reference frame origin and angle uniquely define the coordinate system used to convert pixel image positions to scaled world coordinates. In some videos the coordinate system properties may vary from one frame to the next (e.g., if the camera is zoomed the scale will change, or if panned the origin will change). Tracker makes it easy to handle such videos--see coordinate system for more information.

5. Track objects of interest with the mouse or model them with particle models.

Click the Track Control button to show the track control. Then click the New button and choose a track type from the menu of choices. Most moving objects are tracked using a Point Mass track or modeled using a Dynamic Particle Model track.

If tracking an object, mark its position on every frame by holding down the shift key and clicking the mouse (crosshair cursor) as the video automatically steps through the video clip. Note: don't skip frames--if you do, velocities and accelerations cannot be determined.

You can always adjust a marked position by dragging it with the mouse or selecting it and nudging with the arrow keys. Right-click the video to zoom in for sub-pixel accuracy.

If modeling an object, enter values and expressions into the Model Builder as shown below. The particle will automatically draw itself on the video when played.

You can change the name and appearance of a track by clicking its button on the track control and choosing from the popup menu. Other track control buttons let you show or hide trails, labels, velocity vectors and acceleration vectors.

For more information on tracks and the track control, see tracks. For detailed information on a specific track type, see point mass, center of mass, vector, vector sum, offset origin, calibration point pair, line profile, rgb region, analytic particle model or dynamic particle model.

6. Plot and analyze the tracks

The Plot View displays graphs of track data. Click the x- or y-axis label to change the variable plotted on that axis. To plot multiple graphs, click the Plots button and select the desired number. Right-click on a plot to access display and analysis options in a popup menu.

Two of the most powerful analysis options available from the popup menu are Define... and Analyze....

- The Define... item displays a Data Builder with which you can define custom variables for plots and datatables. Custom variables can be virtually any function of built-in and previously defined custom variables. For help using Data Builder, open Data Builder and click its Help button.

- The Analyze... item displays a Data Tool with statistics, curve-fitting and other analysis capabilities. For help using Data Tool, open Data Tool and click its Help button.

7. Save your work in a tracker (.trk) file

Click the Save button or File|Save As... menu item to save your work in an XML-based tracker file with the extension ".trk". When a saved tracker file is opened, Tracker loads the video, sets the clip and coordinate system properties, and rebuilds all tracks, custom variables and views. For more information see tracker files.

8. Export track data to a spreadsheet

Tracker's Datatable View displays track data in a table. To change the variables included in the table, click the Data button and select from the list displayed.

Data can be easily exported from the datatable by copying to the clipboard and pasting into a spreadsheet or other application. To copy, select the desired data in the table, then right-click and choose Copy Data from the popup menu. For more information see datatable view.

9. Print or copy/paste images for reports

You can print or copy an image of the entire Tracker frame or any individual view (e.g., a plot or datatable). To print the entire frame (all visible views), choose the File|Print Frame... menu item. To print an individual view, right-click the view and choose Print... from the popup menu. To copy an image, choose the desired view from the Edit|Copy Image menu or right-click a view and choose Copy Image. Pasting printed or copied images into notes and reports is an excellent way to document your video analysis results.