What file do you get from a 3D tour (.ply, .spz)

A list. Each entry is one Gaussian: a position in 3D space, a scale on three axes, a rotation, an opacity, and colour information that can vary by viewing angle (stored as spherical harmonics coefficients). A typical interior has one to several million of these. Rendered together from a given camera position, they reproduce the room.

That is all a splat file is. No surfaces, no triangles, no texture images. This is why it renders quickly in a browser and why ordinary 3D tools do not know what to do with it: it is not a mesh and never was.

.ply (Polygon File Format) is an old, general-purpose format for point data. Splat pipelines adopted it because it was already there and every tool could read the header. A .ply splat stores every value in full precision, which makes it large: tens to hundreds of megabytes for a home.

.spz is a newer compressed format designed specifically for Gaussian splats. It quantises the per-Gaussian values and compresses the result, typically producing a file several times smaller than the equivalent .ply with little visible difference. Smaller means faster first load on a phone, which is the whole point of a tour.

Both describe the same scene. Many viewers read both; converters exist to go from .ply to .spz. If a service gives you one, you can usually get the other.

• Host it yourself. Put the file on your own storage and point an open-source WebGL splat viewer at it. The tour then lives on your domain and does not depend on anyone's subscription.
• Open it locally. Desktop splat viewers and some general 3D tools open .ply splats directly.
• Archive it. The file is the record. Keep it with the listing documents.
• Re-upload it elsewhere. Some platforms accept splat uploads; the format is becoming common.

If the vendor only gives you a hosted link and no file, you do not own the tour in any practical sense. You own a bookmark.

• Get measurements. A splat has scale but no guaranteed real-world units unless the pipeline calibrated it, and VOLUME does not claim measurement accuracy. Do not use it for anything that needs a tape measure.
• Get a floor plan. There is no floor-plan extraction in the file. Floor-plan products use different capture.
• Edit it like a mesh. You cannot select a wall and move it. Specialist tools can crop, clean, and merge splats; general 3D modelling software mostly cannot.
• Import it into most game engines without a plugin. Support is growing but not universal.

If you need a measured model, you need a different capture method, usually LiDAR or photogrammetry with scale references. The glossary defines each of these.

An apartment-sized splat is commonly in the tens of megabytes compressed; a large house can be more. The viewer streams or loads the file before the first frame, so size determines how long a visitor waits. This is why the compressed format exists and why a poster image is shown while the scene loads.

Size also depends on the walk. More rooms and more coverage mean more Gaussians. A clean, slow walk produces a tighter, smaller file than a frantic one with the same coverage, because the solver has less noise to represent.