Tunnel, gallery, technical room: a fast survey with the iPhone

What a quick survey is for

A design office, an operator, a utility manager or an inspector does not always have a terrestrial scanner at hand. An iPhone survey keeps a dated record of the state of a place, helps prepare a visit, illustrates a report or shows where a problem was. The markers dropped during the scan (shaft, junction, danger, free marker) give reference points readable on the plan and in 3D.

As for a natural gallery, the principle is a path: you start at a point, you move on, and the plan is drawn behind you, with the distance back to the starting point. This is the core of Lidark, detailed in our guide to quarries, mines and galleries.

What Lidark produces

Each saved survey gives:

• A 2D plan seen from above, as an image or a printable PDF (free).
• A colour 3D model (Lidark Pro) you rotate and measure in the free web viewer.
• An altitude profile and the developed length of the path.
• PLY, OBJ and GLB exports for your desktop software (Lidark Pro), for example MeshLab or CloudCompare.

What Lidark is not: a certified instrument

A Lidark survey is indicative. An iPhone’s LiDAR reaches about five metres with a precision on the order of a centimetre locally, but position tracking is done by camera: over a long path a drift can build up, and a very monotonous, very smooth or wet stretch can degrade tracking. The survey is not georeferenced: it lives in a local frame, with no geographic coordinates.

It therefore replaces neither a topographic survey, nor levelling, nor a terrestrial scan of known calibration. For any regulatory, contractual or safety use, call a land surveyor or a qualified operator. Lidark helps you document fast, not certify.

Prepare a gallery or technical room survey

A few simple rules:

• Enter only where you have the authorisation and training required, with the site’s protective equipment.
• Tell someone your route and do not go down alone.
• Bring backup lighting and a power bank: the iPhone drains quickly while scanning.
• Resume a survey the next day to extend a gallery (Lidark Pro): the app realigns to the same frame.

Site safety: what Lidark does not do

A technical room or an underground structure can present risks that Lidark does not see: electricity, gas, stale air, water, falls. Lidark detects no gas and replaces neither an access procedure nor a suitable detector. Never rely on it as your only way to find the exit: tracking can degrade, the battery can run out, the device can overheat.

Going further

For how it works, see finding your way without GPS or signal and the iPhone’s LiDAR. For a survey of a crypt, a vaulted cellar or a cavity, see crypt, cavity, heritage.

Frequently asked questions