License Plate Recognition @ 75 Meters (246 Feet)

Apparently I have a client who wants to be able to read license plates AND see peoples faces at a gas pump or something along those lines 75 meters away. I did some quick field of view calculations and with analog I get a requirement of 193mm lens, and for an Axis 720p, their calculator is telling me I need 94mm. Both to maintain 100 pixels per foot.

Anyone have any experience with doing license plate recognition at this distance? Right now I'm looking at the Axis P1604-E with a tamron 20-100mm lens, how ever it's not a lens listed on Axis' website, though it is CS mount.


What is the desired Field of View Width?

All my calculations were based on a rather small field of view width, 13 ft with the axis calculator. No field of width has been specified, and I'm hoping to see the site later this week.

I would think 13 ft would be sufficient.

All your math checks out:

1280 (horizontal pixels @ 720p)/13 (feet FoV width) = ~100 PPF, per your goal.

This calculator results in ~92.3mm lens focal length for:

  • 1/3" imager size
  • 250 feet distance
  • 13 feet FoV width

The other big considerations I can think of off the cuff:

  • Is site lighting even and plentiful, especially at night?
  • Will wind/vibration cause the image to shake? Mounting hardware/location is worth looking into.

We have our office demo/test ANPR setup with an Axis Q6035E PTZ camera that detects at a similar distance giving us good results. It has a 20x 4.7-94mm lens which may be suitable for your application.

Daniel,

You don't want to use the Axis P1604-E because there is not enough room in the housing for the lense. You can use an Axis 1604 and an Axis T92A10 Housing.

Acording the Axis' website, the T92E housing is a full 3 inches longer (without sunshield), along with capabilites for -40 (which is currently is outside haha)

Lighting is definitly going to be an issue I am fairly certain, as they've asked for IR capabilities as well. But how well is an illuminator going to work at that distance? I know Axis as their series of illuminators, with a couple models rates for that distance, but I would think the IR could obscure the license plate. Our plates can be somewhat reflective.

As for wind and vibration, I can see that being an issue as well just because of the extreme distance, and the box style camera. The plan was to mount it to the side of the store I believe.

Daniel,

you might be interested in taking a look at the Ampleye Nox-20 camera. We have done some tests with this camera over here, not regarding to license plate recognition, and we were amazed about the image quality that this camera provides. You can take a look at their promotional video in order to have an idea about the camera's potential.

A few notes on Ampleye - You have to use JPEG2000 for the 20MP stream (huge storage costs) and then there is the cost of the camera. Also, they seem to be poorly organized based on our interaction and a number of potential manufacturing partners we spoke to. On the plus side, it appears that IndigoVision just announced an OEM / relabeled version of that camera.