Law Officer Volume 7 Issue 1 No doubt about it, license plate reader (LPR) technology has hit full stride in its value to law enforcement. Around the country, agencies of all sizes are using the technology to find the bad guys. The beauty of LPR is that it functions as both an in-car crook finder and an invaluable investigative tool. Here are a couple of examples.
1) An officer operating an LPR-equipped patrol vehicle is alerted to a vehicle associated with a series of armed robberies being driven in the lane next to the patrol car. After confirming the vehicle is still wanted, a stop is made, a suspect arrested and the vehicle seized for evidentiary processing.
2) An investigator working a child molestation case is looking for a subject who’s gone into hiding. The suspect fled in his vehicle so the investigator checks the local LPR database and finds a couple of LPR reads where the vehicle was ‘seen’ by the LPR in another part of town. Checking this area, the detective locates the car and sets up surveillance to nab the suspect.
The power of LPR as an investigative tool is that every LPR read provides a time, date and location stamp. It’s the location aspect that helps law enforcement zero in on where a vehicle might be found or aid in the identification of a vehicle associated with a series of crimes. In this article, we zero in on the location characteristic of LPR data because it’s both invaluable and potentially problematic.
The Basics
The location information is obtained by a Global Positioning Satellite (GPS) unit that is continually checking the position and logging the specifics with the time and license plate information. This is how it’s supposed to work, and the great thing is that it usually works very well. However, sometimes things go awry. When they do, you can be left without the location information or draw the wrong conclusion about where an LPR read took place.
Here are the most common problems associated with GPS information and tips to make the best of a bad situation.
Location Unknown
The dreaded string of zeroes or ones appears in the location box. This happens when either the GPS unit didn’t boot up with the LPR system or the GPS unit was not receiving information from the satellites. The latter is fairly common when a patrol unit is working in an area incapable of receiving a GPS signal, such as a multilevel underground garage.
Upon first examination, this would appear to be a situation in which you’re just out of luck—location unknown. But where there’s a will, there’s a way—actually a couple of ways.
In the case of underground or sheltered parking, this situation will usually be preceded and followed by active GPS reads: before and after you drive where the satellites can’t see you, you’re in an area where they can. As a result, the non-GPS info reads are almost always preceded or followed by LPR captures with GPS information because the GPS signal is visible right before the patrol car drives into a covered area and shortly after it comes out. So check the reads on either side of the mystery location to see if that will tell you where the read occurred. This won’t tell you exactly where you were, but it gets you close and then you can look for visual clues in the picture, such as parking spot numbers or floor levels to provide additional information.
Speaking of visual clues, don’t forget you can check with the LPR vehicle operator. They may recognize some of the landmarks in the LPR overview photos that will tell you where the car is likely to be found.
The more challenging situation occurs when you have a read with a series of zeroes or ones because the GPS unit wasn’t working properly for a lengthy period of time. This could occur if a cable is loose, there’s an improper booting sequence or the device is defective. Regardless, there could be hundreds, even thousands of reads with no location if the operator didn’t notice the problem. Sometimes, a single read may be the only lead in a major case, and an investigator is desperate to know where a vehicle might be found. This was exactly the situation that occurred when an investigator in Southern California called about a read that had only zeroes in the GPS information field.
The first thing to do when this occurs is look at the reads from immediately before and after to see if the GPS info is there. If so, you have a pretty tight area on which to focus. In this case, though, the LPR car had captured hundreds of reads with no location because the GPS device had not booted properly on start-up. Thanks to some pretty ingenious work, a workaround was achieved. Using the 10 reads on either side of the target vehicle, registration checks were run on each LPR plate read. This provided a series of addresses, which were then plotted on a map and indicated a likely area of interest that was about three square blocks. This was passed along to the investigator, and within an hour, the target vehicle had been located. Clever.
Format Errors
Sometimes everything is working properly, and the location is misinterpreted because of GPS formatting. There are at least four different ways of indicating GPS locations, but confusion most commonly occurs when a GPS read in a degree/minute/second format is interpreted as a degree/decimal minute/decimal second format or vice versa. The formats can look similar and are easily confused.
Without getting into unnecessary discussion of GPS fine points, here’s what you need to know. Be careful when you take a number from an LPR read and drop it into a mapping program not directly associated with an integrated mapping function of your LPR system. This might occur if someone sends you a screen shot or an e-mail with the GPS coordinates and you cut and paste them into an Internet mapping program. It could also happen if a contractor mistakenly puts an improperly formatted GPS location into a system to represent the location of a fixed LPR camera. It can literally put you 30 or 40 miles off from where you should be.
Candidly, I’ve seen this happen a few times, and it can really be embarrassing when you have cars showing up in the ocean or in an area where they could not have been. Note: The system works well when you use it properly but can lead you astray if you’re not careful.
Was It Working?
Finally, be prepared for the inevitable question during a criminal case about how you know the system, specifically the GPS, was working properly. Simply saying the numbers were generated by the satellite system is not going to cut it. One of the most effective and inexpensive ways of demonstrating proper GPS operation comes from one of the smartest LPR operators I have ever met—Deputy Sam Paul of the Los Angeles County Sheriff’s Department. It’s simple but brilliant, and I’ve shared this suggestion with hundreds of agencies during LPR training:
1. Pick a location where you know the patrol car will pass by at the beginning and end of shift, such as a parking lot entrance;
2. Obtain a sample or discarded license plate and mount the plate in a manner that it will be seen by the LPR unit as it passes by;
3. Get a known GPS reading of the location (preferably by someone like a city or county road engineer) and post this number in large letters below the plate on a placard or sign;
4. Place the number of the plate in your alert list as a vehicle of interest for calibration;
5. Establish an operator protocol where the LPR vehicle will be driven by this known plate and location for the purpose of reading the plate; and
6. When the plate is read, an alert will sound and pop up with the photo of the plate and sign showing the known GPS. The operator can visually confirm that the displayed GPS location is consistent with the GPS location indicated on the sign.
The beauty of this system is that it’s quick, almost free and automatically logged with the other LPR data.
Once you have the above setup, you’re ready for the inevitable question: “Officer, how do you know the location was accurately determined?”
Your response: “Because the LPR system was checked at the beginning and end of shift and found to be operating properly.”
If this sounds somewhat like the response and methodology of checking radar equipment, you’re absolutely right. This is the type of question and answer that a court is accustomed to hearing, and you should be prepared because it will happen. Again, special credit to Deputy Paul for this straightforward approach.
Timing
By the way, don’t forget to ensure your LPR system is generating a time signal that’s consistent with your other systems. This is relatively easy to do and should be part of a proper install process. If not done, you could end up inadvertently giving a few minutes either way to a crook’s alibi, not something you want to do.