Measured survey or laser scan? Choosing the right capture for the job

Before anything is designed into an existing building, someone has to measure it. The choice is usually between a traditional measured survey and a 3D laser scan, and picking the wrong one either wastes money or leaves the design team guessing.

What each one gives you

A measured building survey produces drawings: plans, elevations and sections at an agreed scale and level of detail. It records what the surveyor chose to measure, and it's quick to read and easy to hand to anyone with a CAD package.

A laser scan records everything the scanner can see, as millions of measured points. The point cloud is then registered into one coordinate system and can be turned into drawings or a 3D model, but the raw capture keeps every surface, so a question nobody thought to ask at the time can still be answered later without going back to site.

When 2D drawings are enough

• Simple, regular buildings where plans and a few sections tell the whole story.
• Space planning, lease plans and fit-outs that don't touch the structure.
• Jobs where the only question is the size of the rooms.

When scanning pays for itself

• New steel connecting to an existing frame, where the real positions of columns and beams matter more than the original drawings.
• Plant rooms, services-heavy spaces and anything congested.
• Irregular or historic geometry, where walls aren't straight and floors aren't level.
• Live buildings where access is limited: capture once, answer questions for the rest of the project.

Accuracy is its own topic, and a quoted figure needs unpacking before you rely on it. We covered that in what ±2mm actually means in a scan-to-BIM model.

What to ask for

If you commission a scan, agree the deliverables up front: the registered point cloud in an open format such as E57, the coordinate system and control it's tied to, a registration report, and (if you need one) the model, with its level of detail stated. A scan that nobody can open, or that sits in an arbitrary coordinate system, is a cost rather than an asset.