Use the ST_Simplify function to simplify a 3D model - PolarDB

ST_Simplify reduces the vertex count of a 3D scene to decrease storage size without affecting visual output.

Syntax

scene ST_Simplify(scene sc, cstring rules);

Parameters

Parameter	Type	Description
`sc`	`scene`	The scene object to simplify.
`rules`	`cstring`	A JSON string that controls the simplification behavior. See Rules for the full schema.

Rules

Pass a JSON object to rules to configure how simplification is applied. All fields are optional and fall back to their defaults.

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

Field	Type	Default	Description
`mothed`	string	`"percent"`	The simplification method. Valid values: `"percent"`, `"error"`.
`threshold`	number	`0.5`	The simplification threshold. Semantics depend on `mothed`. See Threshold behavior.
`blacklist`	array of strings	—	Mesh names to exclude from simplification. Meshes in this list are left unchanged.
`boundary`	boolean	`true`	Specifies whether to simplify boundary geometry.
`meshes`	array of objects	—	Per-group simplification overrides. Each entry specifies a list of mesh names and a threshold that applies only to those meshes.
`meshes[].names`	array of strings	—	The mesh names in this group.
`meshes[].threshold`	number	—	The simplification threshold for this group, overriding the top-level `threshold`.

Threshold behavior

The meaning of threshold changes based on the mothed value:

`mothed`	`threshold` range	Meaning	Direction
`"percent"`	`(0, 1)`	Ratio of triangles retained after simplification to the original count. A value of `1` retains all triangles (no simplification); a value close to `0` produces maximum simplification.	Lower = more simplified
`"error"`	`(0, +∞)`	Maximum allowed distance (in model coordinate units) from a new vertex to its original position. A larger value permits greater deviation and produces more simplification.	Higher = more simplified

Boundary simplification

Warning

If the boundary is simplified, the model may be collapsed or broken. Test with a copy of your model before applying to production data.

Per-mesh group overrides

Use the meshes field to apply different thresholds to specific mesh groups. This lets you simplify high-detail meshes aggressively while preserving detail in others.

For example, set a high threshold (less simplification) for architectural detail meshes and a low threshold (more simplification) for background geometry.

Examples

The following example simplifies a scene using the percent method with a global threshold of 0.1 (retaining 10% of triangles), excludes three meshes from simplification, and applies custom thresholds to two mesh groups.

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;

Storage impact

Simplification significantly reduces model storage size without affecting visual output.

Simplification settings	Storage size
100% (no simplification)	96 MB
5% geometric + 25% image simplification	2.9 MB

100% (no simplification)

5% geometric + 25% image simplification