I'm happy to report that the Corona Lockdown in Europe also had some positive side
effects: Finally I found time to implement an image history system in midas,
something I wanted to do since many years, but never found time for that.
The idea is that you can incorporate any network-connected WebCam into the midas
history system. You specify an update interval (like one minute) and the logger
fetches regularly images from that webcam. The images are stored as raw files in
the midas history directory, and can be retrieved via the web browser similarly to
the "normal" history. Attached is an image from the MEG Experiment at PSI to give
you some idea.
The cool thing now is that you can go "backwards" in time and browse all stored
images. The buttons at each image allow you to step backward, forward, and play a
movie of images, forward or backward. You can query for a certain date/time and
download a specific image to your local disk. You can even synchronize all time
axes, drag left and right on each image to see your experiment from different
cameras at the same time stamps. You see a blue ribbon below each image which shows
time stamps for which an image is available.
Initially, only the most recent image is loaded to speed up loading time. As soon
as you click on the image or one of the arrow buttons, previous images are loaded
progressively, which you can see in the ribbon bar becoming blue. For slow internet
connections this can take some time. For typical webcams and one minute update
period you get typically a few GB per week.
To make this happen, you define a new ODB subtree
Name: Name of Camera
Enabled: Boolean to enable readout of camera
URL URL to fetch an image from the camera
Period Time period in seconds to fetch a new image
Storage hours Number of hours to store the images (0 for infinite)
Extension Image file extension, usually ".jpg" or ".png"
Timescale Initial horizontal time scale (like 8h)
The tricky part is to obtain the URL from your camera. For some cameras you can get
that from the manual, others you have to "hack": Display an image in your browser
using the camera's internal web interface, inspect the source code of your web page
and you get the URL. For AXIS cameras I use, the URL is typically
For the Netatmo cameras I have at home (which I used during development in my home
office), the procedure is more complicated, but you can google it. The logger is
now linked against the CURL library to fetch images, so it also support https://.
If libcurl is not installed on your system, the image history functionality will be
I tested the system for a few days now and it seem stable, which however does not
mean that it is bug-free. So please report back any issue. The change is committed
to the current develop branch.
I hope this extension helps all those people who are forced to do more remote
monitoring of experiment during these times.