[postgis-users] Which length function should be used for linestrings

[Stephen Woodbridge]

On 4/21/2014 11:25 AM, Raghavan Krishnasamylakshmanaperumal wrote:
> Hi All,
>
> I am trying to make use of linestring's length for one of my route
> detection experiment.
>
> My linestring data is in this format
> "the_geom geometry(LineString,4326)"
>
> I tried using ST_Length(the_geom), ST_Length(the_geom,true) and the
> results are as follows,
>
>     */the_geom geometry(LineString,4326)/*
>       "0102000020E6100000030000008204C58F31C551C070AC8BDB682C4540DA1B7C6132C551C0BF7D1D38672C45403333333333C551C00D4FAF94652C4540"
>
>     /*ST_Length(the_geom)
>     */0.000141421356226931
>
>     *ST_Length(the_geom,true) *i.e spheroid=true
>     13.8305487635736
>
>
>
> What is the metric used for these st_length values? Also if I want to
> use length as my edge cost in a graph formed out of these linestrings
> which length function I should use?

ST_Length() returns the distance is the object units. In 4326 this would 
be degrees

ST_Length on the spheriod is probably in meters.

-Steve