ST_3DDifference
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## Name

ST_3DDifference — Perform 3D difference

## Synopsis

`geometry ST_3DDifference(`geometry geom1, geometry geom2`)`;

## Description

Returns that part of geom1 that is not part of geom2.

Availability: 2.2.0

This method needs SFCGAL backend.

This method implements the SQL/MM specification. SQL-MM IEC 13249-3: 5.1

This function supports 3d and will not drop the z-index.

This function supports Polyhedral surfaces.

This function supports Triangles and Triangulated Irregular Network Surfaces (TIN).

## Examples

3D images were generated using PostGIS ST_AsX3D and rendering in HTML using X3Dom HTML Javascript rendering library.

    SELECT ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
     50, 'quad_segs=2'),0,0,30) AS geom1,
            ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
     50, 'quad_segs=1'),0,0,30) AS geom2;
Original 3D geometries overlaid. geom2 is the part that will be removed. |
    SELECT ST_3DDifference(geom1,geom2)
    FROM ( SELECT ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
     50, 'quad_segs=2'),0,0,30) AS geom1,
            ST_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
     50, 'quad_segs=1'),0,0,30) AS geom2 ) As t;
What's left after removing geom2

## See Also

ST_Extrude, ST_AsX3D, ST_3DIntersection ST_3DUnion

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