Simplify a 3D model with ST_Simplify - PolarDB

Simplifies a 3D model in a scene object based on a JSON rule set.

Syntax

scene ST_Simplify(scene sc, cstring rules);

Parameters

Parameter	Description
`sc`	The scene object to simplify.
`rules`	The simplification rule, in JSON format. See Rule fields for the full specification.

Rule fields

Pass the rules parameter as a JSON object with the following fields:

{
  "mothed": "percent",
  "threshold": 0.5,
  "blacklist": ["wall", "glass"],
  "boundary": true,
  "meshes": [
    {"names": ["m0", "m1"], "threshold": 0.5},
    {"names": ["m2", "m3"], "threshold": 0.001}
  ]
}

Field	Description
`mothed`	The simplification method. Valid values: `percent`, `error`. Default value: `percent`.
`threshold`	The simplification threshold. The valid range depends on the `mothed` value. Default value: `0.5`.
`blacklist`	The names of mesh objects to exclude from simplification. Mesh objects in this list are not simplified.
`boundary`	Specifies whether to simplify the boundary of the model. Default value: `true`.
`meshes[].names`	Groups mesh objects by name for independent simplification.
`meshes[].threshold`	The simplification threshold for the mesh group.

Simplification methods

percent — reduces the number of triangles to a percentage of the original count.

Valid values: (0, 1) (exclusive)
A value of 0.1 retains 10% of the original triangles. Lower values produce more aggressive simplification.

error — controls simplification by the geometric error of the result, measured as the distance from the new vertex to the original vertex.

Valid values: (0, +inf) (exclusive)
Higher values produce more aggressive simplification.

Boundary simplification

Warning

Simplifying boundaries ("boundary": true) may cause the model to collapse or break. Disable boundary simplification for models where edge integrity is critical.

Per-mesh group thresholds

Use the meshes field to apply different thresholds to different parts of a model. For example, apply a higher threshold (less simplification) to high-precision meshes and a lower threshold (more simplification) to low-precision meshes.

Usage notes

Model simplification reduces storage size without affecting the visual appearance in rendering. The table below shows the effect on a sample model:

Simplification setting	Storage size	Result
100% (no simplification)	96 MB
5% geometry + 25% image	2.9 MB

Example

The following example simplifies a scene stored in table t. The global threshold is 10% (retaining 10% of triangles). Three meshes are excluded from simplification via the blocklist. Two mesh groups use independent thresholds.

SELECT ST_Simplify(data,
                    '{
                        "threshold": 0.1,
                        "mothed": "percent",
                        "blacklist":["Mesh.012", "Mesh.009", "Mesh.005"],
                        "meshes": [
                            {"names":["Mesh.007"], "threshold": 0.01},
                            {"names":["Mesh.004"], "threshold": 0.3}
                        ]}') from t;
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