CREATE  [ OR REPLACE ] SPATIAL UNIT OF MEASURE identifier 
TYPE { LINEAR | ANGULAR }
[ CONVERT USING number  ]

The CONVERT USING clause is used to define how to convert a measurement in the defined unit of measure to the base unit of measure (radians or meters). The measurement is multiplied by the supplied conversion factor to get a value in the base unit of measure. For example, a measurement of 512 millimeters would be multiplied by a conversion factor of 0.001 to get a measurement of 0.512 metres.

Spatial reference systems always include a linear unit of measure to be used when calculating distances (ST_Distance or ST_Length), or area. For example, if the linear unit of measure for a spatial reference system is miles, then the area unit used is square miles. In some cases, spatial methods accept an optional parameter that specifies the linear unit of measure to use. For example, if the linear unit of measure for a spatial reference system is in miles, you could retrieve the distance between two geometries in meters by using the optional parameter 'metre':

SELECT geom1.ST_Distance( geom2, 'metre' );

For projected coordinate systems, the X and Y coordinates are specified in the linear unit of the spatial reference system. For geographic coordinate systems, the latitude and longitude are specified in the angular units of measure associated with the spatial reference system. In many cases, this angular unit of measure is degrees but any valid angular unit of measure can be used.

You can use the sa_install_feature system procedure to add predefined units of measure to your database.

Must have DBA authority or be a member of the SYS_SPATIAL_ADMIN_ROLE.

None

• sa_install_feature system procedure
• DROP SPATIAL UNIT OF MEASURE statement
• Using spatial data

The following example creates a spatial unit of measure named Test.

CREATE SPATIAL UNIT OF MEASURE Test
TYPE LINEAR
CONVERT USING 15;