Reality capture

Reality capture, known in Slovak practice as digitalizácia skutočnosti, is the umbrella term for measuring an existing building or site and recording it as digital data. It covers several methods, among them laser scanning, photogrammetry, drone flights and 360-degree photography. For a homeowner or developer planning a renovation, the choice is less about the technology than about which measurement the project actually needs and which files the architect should receive at the end.

What is reality capture?

Reality capture is the process of recording the physical state of a building, a plot or a site as digital measurements, usually as a point cloud, a mesh or a set of images with known positions. The term describes the data acquisition step only. The cost and much of the value sit afterwards, when the data is cleaned, registered into one coordinate system and turned into drawings or a model.

In a renovation the reason is practical. Old houses rarely have drawings that match what was built, and years of small changes, a cut wall or a relocated chimney, make an old plan unreliable. A capture records what is actually there, so design decisions start from measured geometry rather than from memory.

Which capture methods fall under reality capture?

Four methods cover most projects today. They share the goal but differ in how they measure and what they produce.

• Terrestrial laser scanning (terestrické laserové skenovanie) fires a laser from a fixed tripod position and measures distances to surfaces in every direction. It produces the most geometrically reliable point cloud of interiors and facades, at the cost of slower setup and shadows where the scanner cannot see.
• Photogrammetry (fotogrametria) builds a 3D model by computing positions from overlapping photographs taken from many angles. It gives rich colour and texture for little equipment cost, but its geometric accuracy depends on lighting, image overlap and control points.
• Drone capture flies a camera or a laser scanner over the building, the roof or the plot. It reaches roofs, chimneys and gardens that a person cannot measure safely, and it is the usual choice for site context. Drone data is normally combined with ground data for the interiors.
• 360-degree photography records a room from one or a few camera positions. It is fast and inexpensive and works well as a visual record or a walkthrough, but the dimensions it gives are approximate.

How do the capture methods compare for a renovation?

The methods differ most in accuracy, speed and the kind of file they leave behind. Use the table to narrow the field before you talk to a provider.

Which capture should you order for a renovation?

Order the capture that matches the decision you need to make, not the most advanced one. A kitchen refit in a flat with simple walls rarely needs more than a careful measured survey and some photographs. A structural alteration, a roof rebuild or a deep renovation of a family house usually needs measured geometry of the whole building, and that is where laser scanning or photogrammetry earns its cost.

Ask three questions before ordering. Which parts of the building will change? Will the design rely on exact positions of walls, openings and structure? Will a contractor or an engineer work from the data? If the answer to the second or third question is yes, a point cloud with a documented accuracy is the minimum. If the answer is no, a 360-degree record plus a short measured survey of the changed areas is often enough. Mixed projects often combine methods, for example a drone pass for the roof and a scan for the interior.

Which deliverables should you ask for?

The method is only half of the order. What you ask the provider to hand over decides whether the data can be used at all. Name the deliverable in the brief, because a provider will otherwise deliver whatever is cheapest to produce.

Ask for the accuracy report in writing. A provider who cannot state how the data was controlled has not shown that it can carry design decisions. Agree the coordinate system at the same time, because a point cloud in an arbitrary local frame cannot be placed against the cadastral map without extra work.

How is reality capture different from a geodetic survey?

Reality capture records everything visible in dense detail, while a geodetic survey measures a defined set of points to a stated accuracy in the national coordinate system. The two overlap but answer different questions. A geodetic survey is the basis for boundaries, cadastral records and an official porealizačné zameranie (as-built survey) carried out by a licensed surveyor. Reality capture is the richer record that designers work from.

In practice the two are often combined. The surveyor fixes control points with known coordinates, and the scanning or photogrammetry is tied to those points. Without that tie, a detailed model can be internally consistent yet sit in the wrong place on the plot. Check how the capture is referenced before you accept it.

What are common misconceptions about reality capture?

• More points mean more accuracy. Point density describes how finely a surface is sampled, not how close the points are to the true position. Accuracy depends on the instrument, the registration and the control.
• A drone can replace an interior survey. Aerial data shows roofs and sites well, but rooms, and spaces under eaves, usually need ground capture.
• A scan shows what is inside the walls. A scanner records surfaces only. Hidden structure, pipes and the condition of masonry behind plaster need probes, thermography or opening-up.
• A 3D model is the same as a measured survey. A model may be a visual reconstruction. Ask whether it was built from measurements and how those measurements were verified.