Parked Cars & Trigger Zones

svalvasori

svalvasori

Young grasshopper
Oct 8, 2019
38
4
Canada
1. How does everyone deal with parked cars? Unless the new car happens to block the parked car's plate, I get two plates. I'm sending the data to ALPR, is that where the MEMO field comes into play or can I ignore static objects somehow?

2. What is the most successful motion settings/zones for a one camera setup? I find it easy when a car approaches the camera, but less reliable the other direction. If I make the zone too small or to one side, then the plate isn't always captured in that part of the image. Hoping to get some best practices.
 
I use the static images option to reduce the parked cars.


Everyone has a different field of view and angle, so it really comes down to trial and error with your angle, field of view, and height.

Here is mine where I have a zone drawn such that cars going right to left I get the front plate, and the cars going left to right I get the back plate. You can see in my alert images that the vehicles are all centered in the frame doing this approach.

1722660830139.png



Prior to AI in BI, it took a lot of messing around with motion zones to make it happen.

Now with CodeProject you can have it create the image with the plate in it and send that image instead.
 
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That's almost exactly what I was using, but then realized that the motion zone was the only part of the image used for AI recognition. If the plate is outside of that, it doesn't read the plate. Like this:
1742951893476.png

Also wondering about parked cars? I got the same plate 70 times tonight of a parked car. Also as two plates as it was about 50/50 on if a 'D' was actually a D or O.
1742952023786.png
 
It sort of depends on your camera.

Dedicated LPR no-config-possible cameras: Aim and mask is all you can do. Not ideal, but for one of my cameras, I've mounted it very high and aimed it at the middle of the street, and I've only had 1 problem--a 24ft box trucked was tall enough to block it for a little while.

PTZ: I know not many use PTZ for LPR, but I am using one and it's my best LPR camera. I'm using it at 20x zoom, and the IR can capture plates at 250 ft no issues at all. I have a few presets, which moves the lens slight to either side to avoid double parked cars that show up from time to time. Never really had an issue with capturing plates of parked cars with this setup.

Zoom only: This is a 10x zoom camera that is aim at the street where EVERYDAY there is someone doubled parked. If I see it, I use the camera UI to create a privacy mask for the plate. It takes 10 secs to do, but only if I happen to be on my computer already. Then I have presets for zoom that I can trigger from BI or HA, which will zoom in further to avoid the parked plates. This reduces the capture area for plates, but generally I still catch 95% of the cars.

If you are using ALPR Database, I was going to ask Charlie to write some logic to prune plates that are parked. The ai_dump macro gives the location of the plate, if incoming plate matches any a plate that was read within the last 5 mins, and the X and Y coordinates of that plate has not changed, do not write new plate to the database.

This can also be post-processed, meaning write it into the database, then every hour, go back to the database and do a purge. Doing it this way might allow for cleaning up databases that are already polluted.
 
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