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Marble SPZ files are exported in the generated asset coordinate frame. When you render them outside Marble, use assets.splats.semantics_metadata to convert Gaussian centers and Gaussian sizes into metric, ground-aligned coordinates.

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Read the scale metadata

Completed world responses include SPZ URLs and scale metadata together:
The numeric values in this example are representative, not fixed constants. Use the values returned with the world you are rendering. metric_scale_factor converts raw generated asset units to meters. ground_plane_offset places the metric ground plane at y = 0.

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Apply center and size scale

Apply scale to Gaussian centers and Gaussian sizes:
The ground-plane offset applies only to Gaussian centers. Do not apply ground_plane_offset to Gaussian sizes.

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Handle log-scale fields

Some Gaussian splat formats expose scale_0, scale_1, and scale_2 as log-space values. If your decoder gives you log scales, add the logarithm of the metric scale instead of multiplying the log values directly:
Equivalently, convert to linear scale first:
Multiplying scale_0, scale_1, and scale_2 directly is only correct if your decoder exposes those fields as linear sizes.

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Convert renderer axes separately

semantics_metadata converts raw Marble SPZ coordinates to a metric, ground-aligned frame. It does not include renderer-specific axis conversion. Generated Marble SPZ assets use the marble_raw_opencv convention. If your engine uses an OpenGL or Three.js-style frame, apply your engine’s axis conversion after applying metric scale and ground alignment. Marble’s web viewer applies a 180 degree rotation around the X axis for generated SPZ assets.