[Physltest] [Phys-L] Re: details on using Tracker

[Aaron Titus <titus@MAILAPS.ORG>]

I'm replying to the list rather than to Cindy so that others trying
Tracker do not lose heart. It's an open source program that deserves
more than a few minutes of your time. Rotating axes is VERY EASY.
Following the instructions below will take you less than 10 minutes,
I'm sure.

Note: the ctrl-click problem is Mac-specific and I hope that Doug Brown
will change the method used to mark the object or that Apple will use
cmd-click instead of ctrl-click as the right-click, but there's little
chance that Apple would change this.

To get around this annoyance, do the following (note that I include all
steps from the beginning):

(1) open the video; I used a video that came with tracker,
FlexTrackRaces.mov.

(2) Click the "show axes" icon in the toolbar (note: it looks like a
red set of axes like "_|_").

(3) Drag the origin of the coordinate system to the top of the inclined
part of the ramp.

(4) Grab the small vertical line on the +x axis ( it looks like "|" )
and rotate the coordinate system so that the +x axis is parallel to the
ramp.

(5) Click the "show axes" icon again in order  to hide the axes.

(6) Click the "show track control" icon (it has the asterisk in the
icon) in the toolbar. A new floating toolbar called Track Control will
appear.

(7) Click the "New" button in the Track Control toolbar and choose
"Point Mass" from the menu.

(8) Click the "mass A" button that now appears on the Track Control
toolbar and select "Mark by Default" from the menu for mass A.

(9) Step the video forward to the point where the ball is at the top of
the incilne; use the step forward button on the video player buttons
beneath the video.

(10) Click on the ball to mark it; it will advance to the next frame;
continue clicking.

(11) To view the graph, find the very small button (it looks like a
small circle) at the center of the bottom of the window frame (below
the video player) that is used to adjust the height of the bottom edge
of the window. Click and drag this button upward so that there are now
two frames showing.

(12) At the top left corner of this new frame (bottom frame), there is
an icon showing a set of axes ( _|_ ). Click this icon and select "Plot
View" from the menu.

(13) You'll see the x vs. t graph that is linear.

(14) To view multiple graphs or datatables, etc., grab the small button
on the left edge of this bottom window frame and drag it to the right.
It then shows a new window frame on the left and you can use it to view
results of data analysis or whatever.

Note that I should have set the scale first. This can be done by
clicking the tape measure icon in the main toolbar (it looks like
"<--10-->"). Then you can drag the ends and double click the center to
change the value.

Note that you'll have to take off the "Mark by Default" setting on Mass
A if you want to do anything else on the video screen such as changing
the scale. Otherwise, it thinks that you are making the object in the
video. Once again, using "Mark by Default" in this case is an annoyance
that is solely due to the fact that ctrl-click will not mark the object
on a Mac OS.

This is open source software and it gets better due to the collective
efforts of its community of users and the developer(s). Doug is a
really great guy and has poured a lot of time into this project, solely
for our benefit. I encourage you to use this software and give him
constructive feedback. Maybe you can even help contribute to the
documentation.

I agree that finding the graph window is extraordinarily difficult the
first time you use the program. However, once you know how to do it,
you'll never forget it. I hope that Doug will address this issue in the
documentation or in the program itself.

I hope this helps, and I hope you'll give it another try. It's too easy
to rotate axes for you not to give it another try.

Aaron

On Jan 28, 2005, at 3:50 PM, Cindy Schwarz wrote:

> i had problems too - i tried it again - I had your problem at first and
> I had to go into something and set something and then it worked (sorry
> cant remember exactly what) but then after I did the clicking I could
> not get a graph - help said something about a plot window or strip and
> I couldnt ever find that - in the end I decided if it took that long
> for me to figure out and I couldn't get it to work it was not worth it
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