Sensor planning - what has to be settled before mounting
The most expensive decision in a counting system looks like a formality: the mounting height. It is settled on site, often by the ceiling construction - and for years it decides which analyses are possible at all.
If all you want today is to count entrances, you won't notice. If in two years you want to know how the age mix has shifted, or where people look when they stand at the shop window, you'll notice then - as a second installation. This article works through what has to be settled before mounting: which links have to come together for a metric to have data, which height supports which analysis, and which constants determine the number of sensors and the cable routes.
All hardware figures in this article are manufacturer figures and apply per model.
Four links before a metric has data
An analysis doesn't appear because someone switches it on in the software. It appears when four conditions are met at once:
| Link | What it requires | Where it's decided |
|---|---|---|
| 1 Licence | Add-on functions such as gender, age, gaze direction, staff exclusion or object detection are licensed; group counting is included with no extra licence | with the sensor manufacturer |
| 2 Mounting height | Each add-on function has a height window in which the sensor delivers it | at the site survey |
| 3 Configuration | Counting lines and zones are set up on the sensor and named correctly | during sensor configuration |
| 4 Activation | The analysis is enabled for the site | at connection, by us |
If one link is missing, the metric stays empty - not wrong. That's the good news. The bad news is that the first two links are hard to fix after installation. A licence can be bought later. A mounting height can't be licensed later.
Which quantity needs which sensor function, and what each distribution refers to, is covered in What a counter can tell apart. Why the names on the sensor are the contract with the software is covered in Rolling out a counting system.
Mounting height decides the data streams
A 3D sensor looks down from above. The higher it hangs, the larger the area it covers - and the smaller the people below appear. For counting, that makes no difference until well above ten metres. For attributes that need a finer image, it does.
| Model | Mounting height | Coverage per sensor | Demographics and gaze direction | Objects |
|---|---|---|---|---|
| Wide-angle sensor | 2.00 to 6.00 m | up to 10 × 10 m from 3.50 m | 2.40 to 3.25 m | 2.00 to 3.50 m |
| Standard sensor | 2.20 to 6.00 m | 7 × 5 m from 4.50 m | gender and gaze 2.40 to 4.00 m, age 2.80 to 4.00 m | 2.20 to 3.50 m |
| Low-ceiling sensor | 1.95 to 3.50 m | 7 × 5.88 m at 3.50 m | 2.40 to 3.25 m | from 1.95 m |
| Hall sensors | 6.00 to 20.00 m by variant | 8 × 6 m or 12 × 9 m | group counting | group counting |
The most important planning rule follows from this: demographics and gaze direction end at a mounting height of 4.00 metres. Under a high ceiling - an atrium, a station hall, an exhibition tent - a hall sensor counts reliably. If you also want to know who is coming, you need a second, lower sensor level at the points that matter: the entrance, in front of the shop window, at the till.
So the question belongs at the start of any plan: which analyses should the system deliver in three years, not just today? Why that is also a cost question is covered in Total cost of ownership.
Nine constants that set the number of sensors
How many sensors an area needs, where the cables run and how much power the switch must supply follow from a handful of constants. They are manufacturer figures:
| Constant | Value | What it means for planning |
|---|---|---|
| Overlap | at least 30 cm between two sensors | the manufacturer's only explicit planning rule - without it, gaps appear at the edges |
| Family change | at 6.00 m | below it standard and wide-angle sensors, above it hall sensors |
| Below 2.00 m | counting only, door width up to 1.00 m | low passages suit counting, not analytics |
| Cable | at most 100 m per sensor | also the radius of every sensor cluster around its switch |
| Power | PoE class 0, wide-angle sensor up to 12.95 W, other models 7.5 to 8.0 W | 24 wide-angle sensors on one switch need a PoE budget of at least 311 W |
| Mounting angle | ±15 degrees on one axis, ±5 degrees on the other | the critical figure for truss mounting at trade fairs and events |
| Area per sensor | 35 to 45 m² with a standard or hall sensor, 85 to 100 m² with a wide-angle sensor | the rule of thumb for full coverage of an area |
| Sensors per metre of door | at a 3.00 m ceiling, about 0.29 standard or 0.11 wide-angle sensors | a 7 m wide entrance therefore needs about two standard sensors or one wide-angle sensor |
| Light | from 2 lux indoors, from 9 lux for the outdoor model | even dimmed lighting is enough |
The areas per sensor are derived from the coverage tables and calculated with the 30-centimetre rule. They are a planning heuristic for a first estimate. The binding figure comes from the site survey, with the measured ceiling height and the real floor plan.
Two sensors, one door
One mistake happens more often than you'd think: a wide entrance is covered by two sensors, each gets its own counting line, and anyone walking through the overlap is counted by both. The visitor figure is then not off by a few per cent but systematically too high - precisely on the busy days.
The fix sits on the sensor, not in the analysis. Several sensors are combined into one logical sensor that sees the scene as a whole and lets each person cross the line once. According to the manufacturer this works directly with up to 15 sensors (with a wide-angle sensor in the lead) or 9 (with a standard sensor), and with up to 350 through an aggregator. The planning rule is simple: one door, one counting line - however many sensors hang above it.
Who counts, and who doesn't
Two further decisions are made on the sensor rather than in the software, and both change the figure before it arrives anywhere:
- Passers-by. Someone who stops outside and looks in isn't a visitor. So the counting line belongs far enough inside that a glance through the door doesn't trigger it. That's a configuration question, not an analysis question.
- Staff. Employees walking through the entrance twenty times a day distort every metric built on visitors. With staff exclusion, staff wear a small tag and are taken out of the count - on the standard sensor at a mounting height of 2.50 to 3.50 m.
How a movement under the sensor becomes a stored figure, and why no count may be doubled or lost along the way, is covered in From movement to figure. What leaves the sensor in the first place is set out in Privacy is an architecture decision.
What belongs in the tender
- Which analyses should the system deliver today, and which in three years?
- Which sensor model is planned for each entrance and zone, at what mounting height, and does that height sit within the window of every planned add-on function?
- How many sensors does the area need according to the coverage table, calculated with a 30 cm overlap?
- Are wide entrances configured as one logical sensor with one counting line?
- How far behind the door does the counting line sit, and how are staff handled?
- Are the cable routes and the PoE budget of the planned switches sufficient?
- Which licences are needed per sensor, and which analyses must be enabled on the platform?
How we do it
In a rollout of the ANALYSIT Counting System, planning comes first: at the site survey, ceiling heights and door widths are measured, sensor model and mounting height are derived from the sensors' coverage tables, and counting lines and zones are set on the floor plan. We plan against the chain of prerequisites: licence, mounting height within the window of the add-on function, counters and zones on the sensor, and enabling on the platform.
ACS reads the counting logics whose names begin with visitor_logic, passenger_logic or customer_logic, and discovers zones from the data the sensor actually sends. Zones and lines for the security alert are named as restricted areas on the sensor. A combined multisensor arrives in ACS as a finished overall scene and is analysed as one sensor.
If you're planning a system and want to be sure it will still deliver what you need in three years, talk to us. The mounting-height question is cheap before mounting.