What a digital twin is
A digital twin is a digital counterpart of a real object. For buildings, that means the built state is recorded in a form that people who are not on site can understand too.
The term is loose. A digital twin of a building can mean a walkable copy that shows the condition. A digital twin of a factory can just as well mean a simulation model of the plant that calculates throughput. Both carry the same name and solve entirely different problems, so the first question in any project is which of the two is wanted.
Visual twin or data-driven twin?
This is the distinction that decides whether siteviewer fits.
A data-driven operating twin ties a model to reality through data. Sensors report temperatures, states and throughput, the model calculates alongside them, runs scenarios and predicts what happens next. It is a tool for running a plant and planning maintenance.
A visual twin ties a model to reality through the picture. It shows how a building looked on the day it was recorded, including everything no drawing contains: cables pulled in later, shelving that was moved, a temporary barrier that became permanent.
siteviewer delivers the visual twin. Sensors, live readings and simulation are explicitly not part of it. If you are after energy monitoring, a plant simulation or predictive maintenance, you need a different tool, and that is worth settling before a project starts, not after.
How the twin is made
You do the recording yourself, with equipment the company already has. A smartphone is usually enough. A drone covers facades and roofs, and an action cam suits large areas inside and out. From the photos and video, siteviewer reconstructs the surfaces with Gaussian Splatting. No laser scanner is needed.
A twin that mirrors the building goes out of date when the building does. When an area changes, you record that area again the same way and it is merged into the existing model. The effort of an update follows what changed, not how large the building is.
Use in a factory or in building operations
Typical uses are agreeing things across sites, preparing a rebuild or a maintenance job, briefing outside contractors before they travel, and getting new staff up to speed. You can measure directly in the model: distances, areas, rectangles, circles and volumes.
How the as-built state can be kept traceable for operations, maintenance and projects, and where the limits of visual documentation lie, is covered in digital factory documentation. For what moving through the model is like, see the 3D walkthrough page.
How it relates to BIM and CAD
BIM and CAD describe a structure as a data model: components with properties, relationships and dimensions. They say how something was planned.
A visual twin says how it turned out. The two do not exclude each other; the gap between plan and as-built is often exactly the thing you are looking for. But a siteviewer walkthrough is not automatically a dependable CAD or BIM model and does not replace one.
Limits
The twin shows the state on the day of capture, not today's. Anything not recorded does not exist in it: what was not captured is missing, and nothing tells you that something is missing.
Dimensions are not automatically fit for surveying. Measuring is part of the walkthrough, but for a dimension anyone has to stand behind, you still need survey or CAD data made for that purpose.
And, as set out above, sensors, live data and simulation are not part of the method.