.PLY File Format

Introduction

This is the PLY layout that the 3D Gaussian Splatting training code from Inria writes when it saves a scene, as point_cloud.ply. Most splat tools read and write it, and it is the usual starting point for converting a scene to .splat, .ksplat, .spz or the compressed PLY.

Each splat is a vertex. Its properties are the model’s parameters as training leaves them, so a reader applies the same functions the renderer does: the exponential to the scales, the sigmoid to the opacity, and normalisation to the rotation.

Structure

The file is a PLY file with a text header and binary data. The training code writes the data in the computer’s own byte order, which in practice is little-endian. The header declares one element, vertex, whose count is the number of splats, and its properties, all float, in this order. With spherical harmonics of degree 3 there are 62 properties, 248 bytes a splat.

A reader should find the properties by name rather than by position: other programs write the same names with fewer f_rest properties, without the normals, or with extra properties.

In this reference

• Splat properties – every vertex property, and how each becomes part of a Gaussian: sigmoid opacity, exp scale, normalised quaternion and the spherical harmonics

Also used for

• PlayCanvas compressed PLY – Chunks of 256 splats with ranges, and four packed words a splat.
• Polygon File Format – Stanford’s mesh and point cloud format, with a header that declares every property.

Variants

• 3D Gaussian Splatting PLY – the training code’s layout: one float vertex a splat, 248 bytes at degree 3
• PlayCanvas compressed PLY – chunks of 256 splats with ranges, and four packed words a splat

Links