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110 CHAPTER 15. MOTION DETECTOR
agram and select “Hide Control.” This way you can easily unhide them
later should they be needed again.
• Use the IMAQ Copy VI in the (image) analyze state to copy the exist-
ing
qsm.Analyzed image
buffer contents to the
previous image
buffer. Be certain to execute this VI before the Vision Assistant script us-
ing error cluster propagation to control data flow, otherwise your copied
image will always be identical to the current webcam image.
• Create an enumerated selector and a case structure to determine which
of the six images to show on the main image display in the
(image) show
state.
•
Use the IMAQ Quantify 2 VI to determine the maximum and minimum
values in the Velocity Component 1 image, and then use the difference of
these two values as a measure of motion activity to be displayed by the
panel meter.
T
IP
: Use the “Quick Drop” shortcut (Ctrl + space bar) to look up
and place a LabVIEW element by name. See Appendix C on page 139
for more LabVIEW tips.
•
The IMAQ Optical Flow (HS) VI will throw an error if the current frame
and previous frame do not each contain valid images of the same size.
Your application will need to enqueue a special task to select the
(image)
analyze state one time to create the “Analyzed” image before the default
task is selected. In this way the previous image frame will be available
the first time that the optical flow VI is called. Use the
First Call?
function
to detect the very first time that the scheduler runs.
Optional extra features:
You may wish to add one or more of these extra features:
• Add an audible alarm; see Chapter 11 of the NI myRIO Project Essentials
Guide
3
for details on the piezoelectric buzzer.
• Add a time stamp to the image overlay.
• While motion is detected save an image to the USB thumb drive once
every second or so.
3
http://www.ni.com/myrio/project-guide