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Today's Topics:
1. Tracking bats - how to increase the motion detection
frequency? (Andre Zibell)
----------------------------------------------------------------------
Message: 1
Date: Fri, 19 Apr 2019 21:26:54 +0200
From: Andre Zibell <[email protected]>
To: [email protected]
Subject: [Motion-user] Tracking bats - how to increase the motion
detection frequency?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi everybody,
I am trying to set up a raspberry pi3 with NoIR camera and motion in
order to track the activity of bats, so very small, very fast flying
animals. In the worst case I am pointing the camera just at the sky with
IR LEDs for illumination. So the event duration is only a fraction of a
second.
Therefore, to get at least some images from a single bat, I tried to
squeeze the maximum number of frames out of the camera, by using the
following control parameters (motion installed via
pi_stretch_motion_4.2.2-1_armhf.deb). Please feel free to hint for more
optimization.
mmalcam_name vc.ril.camera
mmalcam_control_params -md 7
v4l2_palette 9
width 640
height 480
framerate 90
threshold 300
noise_level 32
disabling despeckle filter
disabling video file output
With these I get rather constant 90 FPS from the camera, being enough
for nice "time-lapse" shots. I prefer the Raspberry Pi v1 Camera over
the v2, since the 640x480 mode of the v2 camera seems to use only the
center part of the sensor, resulting in a smaller field of view.
Now to my question/issue: using the "text_changes on" command I noticed
that the number of changed pixels written to the upper corner only
changes every 30th or so frame, and thus the decision "threshold crossed
or not?" also only happens every ~30th frame. For my application this
leads to the following problems:
1) When this motion detection decision happens when the bat is already
somewhere within the field of view, I miss the pictures of it entering
the field of view. I got around this by setting the pre_capture option to 30
2) When the bat entrers AND leaves the camera field of view in during
these ~30 frames in between these decision cycles, no event is generated
at all, and I miss it.
So my question is: is there an option to have the number of changed
pixels being calculated in shorter intervals, ideally EVERY frame, or at
least every third frame or so? I am aware this would increase the CPU
load, but I am trying to minimize it on the other hand by using no image
processing, no rescaling, writing only jpegs, etc.
Thanks for your ideas and help on this - otherwise the software
perfectly fits my needs for this application :) Maybe you can hint me to
the location for this in the source code, so that I can recompile motion
for this?
Best regards
? Andre
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