Returns the length of a line in dataset units.
If the geometry passed in is a simple point or a simple area, then the length returned will be 0. If it is a complex geometry, the length returned will be the sum of the lengths of each simple line within the complex geometry.
Parameter 1 - any geometry.
Returns: the length of the geometry or null if the parameter is not a geometry.
Note: This function does not fully support 3D geometries. Any 3D geometries will be projected down to 2 dimensions.