Positional Parameters

Positional Parameters

The CPA is charged with implementing the City of Calgary's parking policies. The agency manages on- and off-street public parking facilities and enforcement programs and provides parking advisory services. Calgary has about 6,000 on street spaces located in about 800 zones, along with 7,000 off street spaces in surface lots and parking garages.

In 2007, the CPA replaced all of its parking metres with the ParkPlus system, which allows payment via on-site pay machines or by a registered ParkPlus cell phone account.

Parking enforcement officers use Tannery Creek Systems' autoChalk® digital chalking and LPR system to monitor parking zones throughout the city. The fully automated heads up system is comprised of four cameras, a rugged laptop, two lasers, and a GNSS receiver to determine accurate time and position of observed vehicles. The autoChalk system scans up to two cars per second, at 40 km/h, on either side of the road and takes profile and license plate photos of each parked vehicle. Each autoChalk system daily scans and processes about 2000 vehicles parked on Calgary roads. Calgary has six autoChalk units.

ParkPlus uses the license plate to associate paid parking sessions with a vehicle, hence parked vehicles' license plates are automatically checked to see if they have a paid parking session. Every license plate image with an unregistered payment transaction is reviewed by enforcement officers to verify if there is a parking violation.

Miles Dyck, manager of Parking Enforcement for the CPA, explains, “The electronic system is not 100% accurate, so our officers must look at each unregistered plate to see if there's an error. For instance, maybe the camera reads the letter D as an O or 0. We also, don't issue tickets for vehicles that are actively loading or unloading, so those instances must be manually removed from the system.” All citations are reviewed by a parking enforcement officer before issuing.

Dyck added that the lengthiness of the manual review was compounded by the GPS errors.

“In an urban environment like Calgary with tall structures, our GPS-enabled system could incorrectly locate parked vehicles by hundreds of meters,” he says. “We weren't getting the correct GPS locations for 6-7% of the vehicles-that's about 1,400 vehicles every day that we would have enforcement officers manually review and place in the appropriate parking zones. Our officers were spending 4-5 hours every day reviewing potential parking non-payment violations.”

SPAN Accuracy

To correct the problem, Tannery Creek Systems, developer of the autoChalk solution, recommended that the CPA add the NovAtel SPAN technology GNSS+INS navigation system to the digital chalking and LPR system as a way to minimize the potential for multipath errors.

SPAN combines a GNSS with an Integrated Inertial Measurement Unit (IMU) to bridge GNSS outages for more reliable positioning in challenging environments such as urban canyons. The SPAN-enabled GNSS performance with integrated inertial measurements allows for faster signal reacquisition and faster return to a fixed integer carrier phase solution after signal outage. For Bill Franklin, president of Tannery Creek Systems, the practical user benefits are substantial. He says, “The Novatel SPAN GPS provides amazing accuracy even in harsh deep urban canyons with brutal multipath conditions. We typically see real time accuracy well less than 20 metres even in the toughest of conditions. It's amazing technology.”

In a different project Tannery Creek used post processing, performed by NovAtel's Waypoint Inertial Explorer ® package, to more accurately position vehicles in brutal downtown urban canyons. But the real time accuracy led Tannery to recommend the SPAN solution for use in Calgary.

Franklin commented, “We had tested the SPAN system in another city and were impressed with accuracy even before post-processing. We believed the addition of the SPAN system could map 98% of a city such as Calgary with greater accuracy and better results, namely fewer multipath errors, thus a greater number of vehicles properly located during parking enforcement checks-and therefore less time spent staring at a screen.”

The CPA agreed to test the SPAN system on one of its parking enforcement vehicles in early 2013.

Dyck recalls, “The difference was immediately visible. After piloting the system for several weeks, we were able to cut our unregistered plates from 7% to about 1%.”