Introduction

This section may be of interest to some partners when wanting to compare devices from other manufacturers who use different technology in their counting devices.

Additionally, knowing how a Vector works may assist installers when deciding the best place to site a device, and may assist when trying to fix other issues to do with tracking and count accuracy.

 

Technology

The technology used by Vector devices is that of Time of Flight detection, which is a depth sensing technology.

Other depth sensing technologies include Radar, Ultrasound, LiDAR, Camera based Stereo vision, and 'Structured Light'.

You may have already experienced time-of-flight (ToF) devices without even realising it. If you've ever had an MRA scan in a hospital, or been in a car with advanced driver-assistance systems, you've seen time of flight devices in action. Some of the very latest smartphone cameras even use Time of Flight for advanced focusing and other functions!

If this is your first time hearing about time-of-flight, read on to learn what it is and how it is used in Vector 4D devices.

Time of flight technology is often compared to laser distance finders in that they emit a signal and then measure how long it takes for the reflected signal to return. Because the speed of light is known the distance can be calculated from the time the signal takes to be reflected back.

While this analogy is fitting, a laser measure employs a single beam of light to measure the distance to just one location, but a Vector uses an array of 10 Infrared LEDs to illuminate a much larger area, and then the time of flight sensor is able to measure the reflected signal from many hundreds of different points within that area, all at the same time.


Essentially, the Vector measures distance by actively illuminating an object with a modulated IR light source and a sensor that is sensitive to the IR wavelength, captures the reflected light.

The actual resolution of the time of flight sensor used in Vectors is 80 x 60 pixels.

The sensor measures the time delay ∆ between when the light is emitted and when the reflected light is received by the camera. The time delay is proportional to twice the distance between the camera and the object (round-trip, there and back), therefore the distance can be estimated as depth = cΔ/2 where c is the speed of light.

3D Time of Flight (ToF) | Analog Devices

When installed correctly on the ceiling - pointing straight down - the Vector will see a rectangle shaped area on the ground. 

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This produces a height map of its observable scene which is updated at 15 frames a second. As people walk through the scene the height data will change and the person can be tracked.

Note this is not a thermal image but a height map - the persons head is a bright red because it is closer to the sensor, whereas their feet are yellow/green because they are further away.
Time of Flight technology also means that Vectors are able to measure their own installation height.

 

Tracking

The Irisys tracking algorithms have been developed over the last 20 years, being refined with each generation of Irisys device, and each incremental firmware update. Consequently, the tracking scheme used on Vectors is one of the most advanced and accurate ways of tracking people currently available. 

The algorithms take the height information from the Time of Flight sensor at 15 frames per second.

The algorithms use the data stream to determine: what is the floor; what are other static targets; and consequently - as people move through the field of view - who are the people who should be tracked.

People are tracked consistently through the field of view, from the moment they enter it to the moment they leave it.

To make setup of the devices easier for the user, the time of flight data is shown as each person represented by a round 'target'.

Notice the height information overlaid on top, as well as the track already taken through the field of view.

 

Count Data

Vectors provide count data via the concept of virtual counting lines and virtual count zones.

There are various count modes and other settings available to refine who gets counted, but essentially as long as a target crosses a count line or enters a zone then they will cause an increment to the register associated with that line or zone.

As part of the device configuration the required lines and/or zones must be placed within the field of view correctly so as to work with the tracking functionality and produce the required data outputs.

 

Note that a video view is also provided and this is overlaid on top of the time of flight view in order to provide a human viewable setup. The video component can be switched off and on as required to assist with setup:

Note the direction arrows on the two counting lines shown in this setup. These indicate the direction that you have to cross the line in order to generate a count increment.

In the example above, we can see the doorway visible in the bottom of the video image, with the lines configured around it so as to ensure everyone who walks in through the door will get counted regardless of weather they go straight on, or turn left or right. The Vector is installed on the side of the door inside the room, so this means the green line is counting IN and the red line is counting OUT. Note that some knowledge of how the Vector has been installed is required in order to know what direction each line is counting.

Note that the green line is partially obscured by the red line because they are in exactly the same place. Positioning lines in this way is recommended so as to be sure that all things are counted equally with no other factors influencing the count data.

Count line totals are stored in temporary registers:

There are lots of register types (various lines, zones, etc), but most will simply be an ever increasing total of the number of people counted crossing a line or entering a zone.

Obtaining the count data is then done via one of the many data retrieval methods available. See here for more details on those data retrieval methods.