Saving digitized data
File format
When you save data in Motion Analysis, the program suggests a file name that consists of the name of the movie file (QuickTime or AVI) plus " data" (you can pick any name you want). The data are saved as text (ASCII) files in a basic spreadsheet format, as follows.
Each line of the spreadsheet corresponds to a single movie frame and contains two timing values:
frame count for the event |
elapsed time |
followed by 4 values for each point that was digitized per frame:
X coordinate |
Y coordinate |
instantaneous velocity |
net velocity |
The frame
count is the elapsed number of movie frames since the start of
the event.
Elapsed time is the interval (in seconds)
since the start of the event.
The X and Y coordinates are the spatial
position of the point. With options in the 'Preferences' window (FILE menu), you can select between raw pixels
or distance units (cm, mm, inches, etc.), and whether coordinates are absolute
or indexed relative to the inital point selected in the event (when more
than one point per frame is digitized, the first point in the first frame
is used as the reference).
The instantaneous velocity is calculated
from the frame interval (1/frame rate) and the distance moved between the
current point and the immediately previous point. It is set to zero for
the initial point in the event.
The net velocity is is calculated from
the elapsed time and the distance moved between the current point and the
initial point in the event. It is set to zero for the initial point in the
event. Note that you can adjust the net velocity measurement (if a movement
under study did not start with the first frame in the sequence) with the
Recalculate net velocity option.
Distance is is calculated from the first
digitized point (the initial point, if more than one point is digitized
per frame), using the current distance unit. Saving distance data is optional,
see the 'Preferences' option in the FILE
menu.
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