Vernier Video and Logger Pro Guide - Manual (Page 3)

Video in Logger Pro 2011 3
Set Scale When you mark points on the movie, the
program initially records the coordinates of each point
in screen pixels. Setting the scale allows you to convert
those coordinates to a physical measurement, e.g.
meters. In the example shown above, a meter stick
appears in the same plane as the motion. That meter
stick can be used to set the scale. Click this button, and
then drag across an object of known length in your movie. Record that distance in the
resulting Scale dialog. Note that the reference scale object must be in the same plane as the
motion, or parallax error will create proportional scaling errors.
Photo Distance Use this tool to measure a distance on the video after setting the scale.
This is essentially the inverse function to setting scale; you draw a line on the video, and
Logger Pro provides the distance.
Set Active Adds new point series for tracking additional objects, and selects between
existing series. If a series has not been used before, the button adds new x,y columns and
creates a new series to track a new object. The active point set is indicated in the popup
menu. If there are two or more point series, use the menu to create a center of mass
calculation. You can assign each tracked object a mass, and then Logger Pro will find the
location of the center of mass of the objects in each frame. The CoM can then be plotted on
the video, and graphed or used in other calculations.
Toggle Trail Displays or hides all the points that have been added up to the current time.
Show Origin: Display the origin on the movie object. Click again to remove the origin.
The origin is set with the Set Origin button
Show Scale: This will show the line that was used when setting the scale (see Set Scale).
Movie Options
A number of important settings are found in the
Movie Options dialog, accessible either by
selecting the video and choosing Movie Options
from the Options menu, or by double-clicking
the movie when not in add point mode.
Of particular note are the options to:
• Override the frame rate when the video is
not marked with the correct frame rate.
• Set the time associated with the First VA
point to zero. This option will “start the
clock” at the first marked frame,
regardless of the time stamp on the
frame.