Cave mapping with an iPhone: a step-by-step guide

What the iPhone can and cannot do

The iPhone’s LiDAR measures up to about 5 metres, including in the dark. In a modest-sized gallery with rough walls, it rebuilds a faithful three-dimensional shape. In a large chamber whose walls are out of range, it only maps what is close.

So it does not replace a survey: no calibrated sights, no guaranteed accuracy, and possible drift over long distances. See it as a complement for volume and path. For the principle of the sensor, read the guide to iPhone LiDAR scanning.

Step 1: prepare the trip

Before going down, on the cave side and the phone side:

• Confirm the access permission, the weather (a flood can close a cave) and your return time, given to someone you trust.
• Charge the iPhone, carry a power bank and a waterproof case: visual tracking, LiDAR and the torch all draw power.
• Free up storage, turn off notifications and try Lidark on the surface to get used to its alerts.
• Plan a mount or a lanyard: an iPhone dropped in water or mud is an iPhone lost.

Step 2: lighting

LiDAR measures without light, but ARKit places the iPhone using the camera: it needs light. Lidark turns the torch on automatically in the dark, and your headlamp lights the walls you sweep. Always carry two sources independent of the phone: the headlamp guide details the rule of three lights.

When you look at the screen, switch on night vision: a moon button turns everything red so you do not dazzle your own eyes.

Step 3: scanning technique

The quality of the survey comes down to how you walk:

• Start the survey at the entrance, so everything is referenced to it.
• Hold the iPhone at chest height and move slowly, without jerks.
• Sweep the walls, the ceiling and the floor, not just the corridor ahead.
• Slow down at junctions and level changes.
• On an alert (“too fast”, “not enough detail”), stop, light a wall rich in relief and resume: nothing is recorded while tracking is unreliable.

Step 4: dropping landmarks

Landmarks are your survey notebook. Drop one at each junction, each shaft or step, each obstacle or danger, and at points of interest. They stay visible on the minimap, the plan and the 3D view, and help you get your bearings on the way back as well as reread the survey later.

If the path forms a loop, Lidark detects it and offers a shortcut to the exit. Take it only if you recognise the passage: the distance shown is that of the path already walked.

The limits to keep in mind

A few situations degrade tracking, and you should anticipate them:

• Large chambers: beyond about 5 metres, the walls are no longer measured. Follow them along.
• Smooth or shiny surfaces: water, very uniform clay, wet walls, which reflect infrared poorly.
• Mist and suspended dust, which disturb the camera.
• Drift: small errors build up over long distances. The survey is indicative.

Step 5: export and open the model

Back at the surface, the survey shows as a 2D plan and an altitude profile. With Lidark Pro, the 3D view removes the ceilings and the PLY or OBJ export opens the model elsewhere. Drop the file into the free 3D viewer: it stays in your browser, with measuring and ceiling removal. MeshLab, CloudCompare and Blender work too.

Combining LiDAR with traditional survey

Cave survey remains the reference. A modified laser meter such as the DistoX, paired with an app such as TopoDroid on Android, records length, azimuth and slope for each shot, with a rigour the phone does not have. These measurements produce the cave’s skeleton, which you then process in survey software.

Lidark does not export a survey format: it provides a PLY or OBJ mesh. Nothing stops you overlaying them in CloudCompare or Blender, aligning the model on your stations, to obtain the volume around the skeleton. See also the guide to caving.

After the trip: review and compare

The real work often starts at the surface. Review the survey as a 2D plan, spot the poorly covered areas, then compare with the cave’s sketch or survey. A dated model also lets you compare two visits: has a chamber filled with sediment, has a passage collapsed? Keep the exported file with your trip notes, in a dated folder.

If you want to go back and complete a sector, resuming a survey (Lidark Pro) lets you return to an area already scanned and extend the model in the same frame.

Safety and ethics

Lidark is an orientation aid: it replaces neither a guide, nor a rope, nor a prior reconnaissance. Do not go down alone, respect the regulations and the rules of your club or federation, break no formations and leave nothing behind. Find all our guides on the guides page.

Frequently asked questions