Digital video motion analysis: Analyzing

3. Analyze the edited shots (using VideoPoint).

• Open the "VideoPoint" application (you can find it in under the Miscellaneous submenu on the Apple menu, under Windows the application is called "Videopoint", or in a Mac under the Apple Menu select "Miscellaneous" and choose "VideoPoint:" a folder window appears; double click on the VideoPoint icon). Note: VideoPoint is "District Supported Software"
• Click on the "About VideoPoint" window to get rid of it.
• Click on "Open Movie" then find one of the shots you edited with MoviePlayer (or use Netscape to download a movie off the web and save it to disk, then open it in VideoPoint).
• You then see the first frame of the shot and a confusing message: unless you are analyzing collisions you are usually locating just one object.
• When the movie window appears, find the object you want to locate, point at it and click. You have collected a videopoint! After you click, notice that the next frame in the movie automatically appears, so that you can just keep on clicking.
• To make the movie window larger, select "Double Size" under the "Movie" window.
• To see the trajectory, choose "Leave/Hide Trails" under the "Edit" menu.
• To create a scale for your videopoints, select "Scale Movie" under the "Movie" menu and follow the instructions. If you included a meter stick in your movie you are set (in a movie with a basketball, you can use the fact that the diameter is 23 cm (0.23 m). For a movie with a person, use their height).
• To make a graph select "New Graph" under the "View" menu. You will need to select your Horizontal and Vertical axis variables, then click "OK" before your graph will appear.
  In addition to position and velocity versus time, try these graphs.
  • Trajectory
  • Horizontal axis= Point S1:x:Position.
    Vertical Axis=Point S1:y:Position
    Notice that if you click on a point in the plot, the movie jumps to the corresponding frame. (This is true for other types of plots also).
  • Velocity Trajectory
  • Horizontal axis= Point S1:x:Velocity.
    Vertical Axis=Point S1:y:Velocity
    To check for constant acceleration: Does it look like the points fall approximately on a straight line with equal spacing?
• To save your data and graphs, select "Save" or "Save As" under the "File" menu.
• To print a window, click on that window, then select "Print Window" under the "File" menu.
• To analyze another movie with the same scale and types of graphs, click on the top bar of the movie window, then select "Switch Movie" under the "Options" menu. VideoPoint will warn you that you will erase the current data, but that's what you want if you have saved your file as described in the previous step. When the new movie appears, just click on the movie to make more videopoints: notice that the points automatically show up in the existing graphs [but you may have to change the scale in some graphs to see some of the new points].

Intro