# ST_3DDistance

## Name

ST_3DDistance — Returns the 3D cartesian minimum distance (based on spatial ref) between two geometries in projected units.

## Synopsis

``` float ST_3DDistance ( ``` geometry g1 , geometry g2 ``` ) ``` ;

## Description

Returns the 3-dimensional minimum cartesian distance between two geometries in projected units (spatial ref units).

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

This function supports Polyhedral surfaces.

This method implements the SQL/MM specification. SQL-MM ?

Availability: 2.0.0

Changed: 2.2.0 - In case of 2D and 3D, Z is no longer assumed to be 0 for missing Z.

Changed: 3.0.0 - SFCGAL version removed

## Examples

```-- Geometry example - units in meters (SRID: 2163 US National Atlas Equal area) (3D point and line compared 2D point and line)
-- Note: currently no vertical datum support so Z is not transformed and assumed to be same units as final.
SELECT ST_3DDistance(
ST_Transform('SRID=4326;POINT(-72.1235 42.3521 4)'::geometry,2163),
ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45 15, -72.123 42.1546 20)'::geometry,2163)
) As dist_3d,
ST_Distance(
ST_Transform('SRID=4326;POINT(-72.1235 42.3521)'::geometry,2163),
ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry,2163)
) As dist_2d;

dist_3d      |     dist_2d
------------------+-----------------
127.295059324629 | 126.66425605671
```
```-- Multilinestring and polygon both 3d and 2d distance
-- Same example as 3D closest point example
SELECT ST_3DDistance(poly, mline) As dist3d,
ST_Distance(poly, mline) As dist2d
FROM (SELECT  'POLYGON((175 150 5, 20 40 5, 35 45 5, 50 60 5, 100 100 5, 175 150 5))'::geometry as poly,
'MULTILINESTRING((175 155 2, 20 40 20, 50 60 -2, 125 100 1, 175 155 1), (1 10 2, 5 20 1))'::geometry as mline) as foo;
dist3d       | dist2d
-------------------+--------
0.716635696066337 |      0
```