.KSPLAT File Format – Headers

GaussianSplats3D splat buffer

A .ksplat file opens with a 4096-byte header, followed by a 1024-byte header for each section. Both are mostly unused space. This page follows SplatBuffer.js in GaussianSplats3D, which writes version 0.1. All numbers are little-endian.

Compression levels

LevelCentreScaleRotationColourHarmonicsBytes a splat at degree 0, 1, 2
03 × float323 × float324 × float324 × uint8float3244, 80, 140
13 × uint16, in a bucket3 × half4 × half4 × uint8half24, 42, 72
23 × uint16, in a bucket3 × half4 × half4 × uint8uint824, 33, 48

“Half” is the IEEE 754 16-bit floating point number. The splat record itself is on Sections and splats.

The harmonics range

At level 2 each spherical harmonics coefficient is a byte u, which stands for u / 255 × (max − min) + min, with min and max from offsets 36 and 40. When either is 0, the reader uses −1.5 for the minimum or 1.5 for the maximum: half of the library’s 8-bit range constant, 3. The writer stores a coefficient v as ⌊(v − min) / (max − min) × 255⌋, clamped to 0 to 255.

The section header

maxSectionCount section headers follow the file header, 1024 bytes each, from offset 4096.

OffsetSizeTypeFieldMeaning
+04uint32splatCountThe splats in this section
+44uint32maxSplatCountThe splat records the section has room for
+84uint32bucketSizeThe splats in a full bucket
+124uint32bucketCountThe buckets, full and partly filled
+164float32bucketBlockSizeThe width of a bucket’s cube
+202uint16bucketStorageSizeBytesThe bytes a bucket centre takes: 12 at levels 1 and 2, 0 at level 0
+222Not used
+244uint32compressionScaleRangeWhat a centre offset counts up to; 0 means the level’s default, 32767 (1 at level 0)
+284uint32storageSizeBytesThe bytes of this section’s data
+324uint32fullBucketCountBuckets with bucketSize splats
+364uint32partiallyFilledBucketCountBuckets with fewer, whose lengths are stored with the data
+402uint16sphericalHarmonicsDegree0, 1 or 2
+42982Not used

The section data starts after the last section header, at 4096 + 1024 × maxSectionCount, and each section’s data follows the one before, storageSizeBytes long. Splats are numbered across sections, each section starting after the previous section’s maxSplatCount.