How to Map 3D Spaces Using Smartphone LiDAR

Q: How do you calculate physical distance from a LiDAR light pulse?

Distance uses the basic speed formula: Distance equals light speed multiplied by round-trip time, divided by two. Dividing by two accounts for the pulse traveling out to the object and bouncing back to the sensor detector.

Smartphone LiDAR maps 3D spaces by firing thousands of invisible infrared laser pulses per second, measuring their reflection return times to calculate exact distances, and combining this with motion sensors to construct a real-time 3D point cloud.

Advanced ⏱ 30-45 min ⚗️ Class 9-12 🏠 Everything is already at home

Time: 30-45 min
Difficulty: Advanced
Best for: Class 9-12
Subject: Physics
Things needed: 4, all at home
Steps: 13
Cost: Free, nothing to buy
You will learn: LiDAR Time-of-Flight and Optical Distance Measurement

How to Map 3D Spaces Using Smartphone LiDAR, Experiment · 11-12 | jijnas.com

Before you start

What you need

0 of 4 ready

Tap each thing once you have it in front of you. Items with the house sign are already somewhere in your home.

🏠 Smartphone or tablet equipped with a LiDAR sensor (such as iPhone 12 Pro or newer Pro models, or iPad Pro 2020 or newer) 1 No luck? Use standard smartphone using a photogrammetry app like Polycam in camera mode.
🏠 3D Scanning Application (such as Scaniverse, Polycam, or 3D Scanner App) 1 app
🏠 Measuring tape (5 meter) for verifying actual dimensions 1 No luck? Use tailor tape or a long plastic scale.
🏠 Test target (such as a desk setup, chair, or small indoor room area) 1 space

💬 Send to a parent

Think first

What do you think will happen?

Real scientists guess before they look. Write one line now. After the steps, the page will show it next to what you should see.

Safety first.

Maintain spatial awareness of your surroundings while looking at the screen during a scan to prevent tripping or bumping into obstacles.

Do it

The procedure

Tap a step when it is done. Lab mode shows one step at a time in big letters, reads it aloud if you want, and keeps the timer.

Launch your chosen 3D scanning application on your LiDAR-equipped mobile device.
Inspect your intended scanning path to clear away obstacles and plan a continuous movement route around the target.
Select the target object size or manually set the scanning range boundary in the app settings to exclude background clutter.
Position yourself at a distance between 0.2 meters and 5 meters from the surface of the target object.
Press the start button within the scanning application to begin recording depth data.
Move slowly around the target while holding the device at a steady distance and angle relative to the ground.Maintain continuous spatial awareness of your physical surroundings to prevent tripping or bumping into obstacles while looking at the screen.
Pause the scan within the app whenever you need to adjust your stance or change your viewing height.
Resume recording and sweep the camera over any uncaptured areas highlighted by the application.
Tap the stop button inside the application to finish capturing depth readings.
Review the preliminary 3D point cloud model on your screen to ensure all critical geometric details were recorded.
Initiate data processing in the application to convert the captured laser readings into a high-density point cloud.
Export the final point cloud file in a compatible 3D format for your project needs.
Measure the real dimensions of the scanned target using a tape measure to verify the scale accuracy of your digital model.

01 · The idea

The Concept

Modern mobile devices use light detection and ranging sensors to map physical spaces in real time. By capturing distance measurements across an area, your phone turns physical objects into accurate 3D digital models.

02 · What you should see

Observation

As you sweep the smartphone across a room, the screen dynamically renders an incremental 3D digital mesh or dense point cloud over the real-world view. Unscanned areas appear as empty gaps, while covered surfaces are filled in with spatial coordinates overlaid with camera colors.

Point Cloud Resolution: The depth sensor generates grid maps (often around 256x192 depth points per frame at up to 60 Hz), yielding tens of thousands of spatial distance points every second.
Measurement Accuracy: For objects within 0.2-5 meters, distance measurements are accurate to within 1-2% of actual room dimensions.
Surface Quirks: Solid, matte surfaces render clean spatial boundaries, whereas transparent glass or highly reflective mirrors cause visual distortions or missing digital geometry due to light passing through or scattering away.

03 · Why it happens

Why It Happens

This spatial mapping works on the principle of Time-of-Flight (ToF). The phone emits invisible infrared laser pulses that strike physical objects and bounce back to an optical detector. By measuring the ultra-tiny time delay between emitting the light beam and receiving its reflection, the software calculates the precise distance to each point on the object.

Think of it like throwing thousands of microscopic rubber balls at a wall simultaneously. If you know the exact speed of the balls, measuring how long each ball takes to bounce back to your hand tells you exactly how far away different parts of the wall are.

04 · The science

The Science Behind It

LiDAR (Light Detection and Ranging) applies fundamental ray optics and electromagnetic wave propagation. Since light travels at a constant high speed (c ≈ 3 × 10⁸ m/s), the physical distance (D) to a surface is derived using the simple velocity-time relation:

$Distance (D) = c × Δ t2$

where Δ t is the round-trip travel time of the infrared pulse. The factor of 2 accounts for the light traveling to the target and back.

In modern smartphones, a Vertical Cavity Surface Emitting Laser (VCSEL) array emits pulsed infrared beams. An optical sensor detects the returning photons. Simultaneously, the device combines these depth measurements with data from its onboard Inertial Measurement Unit (accelerometers and gyroscopes) via Simultaneous Localization and Mapping (SLAM) algorithms. This continuous tracking stitches millions of individual depth coordinates into a unified, georeferenced 3D point cloud.

05 · Take it further

Make It a Project

Turn this mapping setup into a full science fair investigation by testing how physical variables alter spatial tracking accuracy:

Independent Variables: Surface material reflectivity (matte drywall, glass, glossy metal, black fabric), scanning distance (0.5 to 4.0 meters), and room illumination (lux levels).
Dependent Variables: Distance measurement percentage error (compared to a physical tape measure control), depth point density, and spatial deformation.
Controlled Variables: Mobile device model, scanning software app, scanning movement speed, and device inclination angle.
Data to Record: Measure physical benchmarks with a tape measure, compare them to app-derived digital dimensions, and plot percentage error graphs against object distance or surface texture.

06 · Questions students ask

FAQs

What is the effective distance range for smartphone LiDAR sensors?

Smartphone LiDAR sensors typically operate best between 0.2 meters and 5 meters. Beyond 5 meters, the low-power infrared laser beams scatter too much for the sensor to detect faint returning reflections accurately. Direct sunlight can also interfere with distant readings.

Why do glass and mirrors fail to map correctly in LiDAR scans?

LiDAR relies on infrared pulses bouncing directly back to the detector. Glass lets light pass right through, causing the sensor to measure objects behind it. Mirrors reflect light away at angles, creating false distance calculations or completely invisible gaps.

How does the smartphone know its location while building a 3D scan?

The smartphone uses Simultaneous Localization and Mapping, or SLAM. It combines LiDAR depth measurements with real-time motion data from internal gyroscopes and accelerometers. This tracks exact camera movement, correctly stitching individual depth frames into one seamless 3D model.

Do you need ambient room lighting to create a 3D LiDAR scan?

No, LiDAR generates its own invisible infrared light, so it can measure depth in pitch darkness. However, low light prevents the RGB camera from capturing color textures, resulting in untextured geometry without visual surface colors.

How do you calculate physical distance from a LiDAR light pulse?

Distance uses the basic speed formula: Distance equals light speed multiplied by round-trip time, divided by two. Dividing by two accounts for the pulse traveling out to the object and bouncing back to the sensor detector.

Write it up

Your lab notebook

Two minutes here and your lab record is done. Everything stays on this device until you copy it out.

Did it work?

What I actually saw What I would change next time

💼 Same science, as a real job

The physics or chemistry on this bench is what a working business charges for. See the numbers, the licences and the worst case before anyone spends a rupee.