# Interactive Radar for Touch Walls and Floors: What to Check and How to Install It

> In China's installation industry, "interactive radar" usually means a 2D laser scanner (LiDAR), not a microwave radar. Mounted beside a wall or floor, it sweeps a thin plane of infrared light and reports where hands or feet break it. It works well indoors when the scan plane, range, surfaces and lighting are planned before installation.

**Published:** 2026-10-01 - **By:** MLABART

## What does "interactive radar" actually mean?

When a Chinese supplier quotes "radar interaction" (雷达互动) for a touch wall or an interactive floor, the device is usually a 2D laser scanner -- a LiDAR that spins a laser across a flat fan and measures the distance at each step. Microwave (mmWave) radar is a different tool, used mainly to detect presence and approach; our sensing guide compares the two.

A widely used model is the Hokuyo UST-10LX. Its official specification lists a 270° scan angle, 0.25° angular resolution, a 25 ms scan, a 905 nm Class 1 laser and an Ethernet interface. We use its published figures below because they are typical of the category; other brands and models differ.

- [Related: Radar, camera or depth sensor? Choosing the sensing layer](https://mlabart.com/insights/motion-sensing-for-interactive-installations/)

## What should you check before choosing the position?

Six checks decide whether a radar wall feels precise or frustrating. The published figures are from the Hokuyo UST-10LX specification.

| Check | Why it matters | Published figure (UST-10LX) | What to do |
| --- | --- | --- | --- |
| Target colour | Dark, light-absorbing targets return less light | 0.06-10 m on a white target; 0.06-4 m at 10% reflectance | Size the zone for dark sleeves and dark floors, not for a white test card |
| Beam spacing | Neighbouring laser steps spread apart with distance | 0.25° between steps -- about 17 mm apart at 4 m and 35 mm at 8 m (our arithmetic from the spec) | Keep fingertip-sized targets close; on large walls add a second sensor rather than relying on the far end |
| Ambient light | Strong light can blind the receiver | Less than 15,000 lx; avoid direct sunlight | Treat indoor use as the default and shade any window that lights the scan plane |
| Occlusion | One hand hides another along the same ray | Not a spec item -- it is geometry | For multi-user walls, mount sensors at two corners |
| Accuracy | Reported positions jitter by centimetres | ±40 mm accuracy; repeatability σ < 30 mm on a white target | Do not design buttons smaller than the jitter; smooth positions in software |
| Temperature | Outside the range, readings fail | −10 °C to +50 °C | Ventilate enclosed kiosks and summer outdoor sites |

## How do you install a radar on a touch wall?

The same sequence works for most 2D LiDAR touch walls:

- Mount the sensor beside the projected area -- usually at a top or side corner -- on a rigid bracket. Any wobble moves every touch point.
- Set the scan plane parallel to the wall and only a few centimetres in front of it, so a hand registers on contact rather than while hovering.
- Check that the plane is clear. Frames, trim, sockets or a skirting board cutting into the fan create permanent false touches; mask them in software or move the sensor.
- Calibrate by marking the corners of the projected image; the software maps sensor coordinates onto screen coordinates.
- Send touch positions to the content engine -- TUIO or UDP are common -- and check latency and accuracy across the whole surface, including the far corners.
- Test in real conditions: dark sleeves, several people at once and the venue's actual lighting.

- ![Front and side view of a radar touch wall: the sensor in the top corner sweeps a fan across the projected image, with 4 m and 10 m range arcs, and the scan plane runs parallel to the wall a few centimetres in front of it.](https://mlabart.com/insights/interactive-radar-lidar-installation-guide/radar-touch-wall-setup.svg) -- A 2D LiDAR mounted at the corner sweeps a thin plane just in front of the wall. Range arcs are from the Hokuyo UST-10LX specification: 10 m on a white target, 4 m at 10% reflectance.

## How is an interactive floor different?

On a floor, the sensor sits low at the edge so its fan sweeps just above the surface. It sees ankles and feet, not bodies, and in a crowd one person's legs hide another's -- so busy floors need more than one sensor.

Dark or glossy floor finishes cut the usable range in the same way dark clothing does. An IP65 rating keeps dust and water out, but it says nothing about a kick: protect floor-level sensors with a guard that does not cut into the scan plane.

## What are the common faults, and how do you fix them?

Most radar problems show up in the first hour of testing. They map to a small set of causes:

| Symptom | Likely cause | Fix |
| --- | --- | --- |
| Touches register before the hand reaches the wall | Scan plane too far in front of the surface | Bring the plane closer and re-level the bracket |
| Dead spots in the far corners | Beam spacing or dark targets beyond reliable range | Add a second sensor or shorten the distance |
| A permanent ghost touch | Something cuts into the scan plane -- trim, a socket, a frame | Mask that region in software or remove the obstruction |
| The second visitor is ignored | Occlusion behind the first visitor's hand | Add a sensor at the opposite corner |
| Erratic in the morning, fine at night | Sunlight reaching the sensor or the scan plane | Shade the window or move the sensor |
| Touch offset grows over days | The bracket has shifted | Use a rigid mount and recheck calibration on a schedule |

- ![Five failure modes of a radar touch wall drawn as small diagrams: occlusion, beam spacing, dark targets, sunlight and objects in the scan plane.](https://mlabart.com/insights/interactive-radar-lidar-installation-guide/radar-five-faults.svg) -- Five things that break a radar wall. Specification figures are from the Hokuyo UST-10LX; the beam spacing is our arithmetic from the 0.25° angular step.

## Sources

Specification figures are quoted from the manufacturer's documents. Positioning advice is general practice; site conditions vary.

- [Hokuyo -- UST-10LX specification (PDF)](https://www.hokuyo-aut.jp/dl/UST-10LX_Specification.pdf)
- [Hokuyo USA -- UST-10LX product page](https://www.hokuyo-usa.com/products/lidar-sensors/ust-10lx)
- [Derivative (TouchDesigner) -- LidarTracker component](https://derivative.ca/community-post/asset/lidar-component-lidartracker)
- [arXiv -- physics-based simulation of continuous-wave LiDAR (dark surfaces read closer on low-energy LiDAR)](https://arxiv.org/pdf/1912.01652)


## FAQ

### Is "radar interaction" the same as LiDAR?

In China's installation industry it usually is: "radar" for a touch wall or interactive floor means a 2D laser scanner. Microwave radar is a different sensor, mostly used to detect presence and approach.

### How far can an interactive radar detect a hand?

It depends on the target. The Hokuyo UST-10LX specification lists 0.06-10 m on a white target but 0.06-4 m at 10% reflectance, so dark clothing and dark floors shorten the reliable range.

### Can interactive radar work outdoors?

With care. The UST-10LX specification lists ambient light below 15,000 lx and warns to avoid direct sunlight, so shaded or indoor positions are the default.

### How many radars does a large touch wall need?

One sensor can cover a small single-user wall. Large walls and multi-user walls usually need a second sensor at the opposite corner, because one visitor's hand can hide another's and the gaps between laser steps widen with distance.



## Related Pages

**See also:** [Motion & Body-Tracking Interactives](https://mlabart.com/solutions/motion-tracking-interactives/) | [Interactive LED Walls & Big Screens](https://mlabart.com/solutions/interactive-led-walls/) | [Projection Mapping](https://mlabart.com/solutions/projection-mapping/)

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**MLABART** -- Interaction - Imagination - Innovation

MLABART is an interactive installation and interactive software development studio. We design, program and deliver interactive installations -- motion-sensing games, touch and AI experiences, interactive LED walls, projection mapping, naked-eye 3D and kinetic sculptures -- for mall and New Year's Eve countdown campaigns, trade-show booths and launches, and brand pop-ups, from concept and custom software through fabrication and on-site delivery.

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