# [postgis-users] Newbie - get total distance travelled from query ofpoints

Paragon Corporation lr at pcorp.us
Sun Jun 22 14:20:36 PDT 2008

Joe,
You need to convert to some sort of foot or meter projection that is

Then once you've figured out the SRID of that - then transform

SELECT ST_Length(St_MakeLine(ST_Transform(point,rightsridgoeshere))))/1000
as distance

FROM (
SELECT point FROM points
ORDER BY timestamp
) as p

Some good places to figure this out
1) PostGIS Wiki
http://postgis.refractions.net/support/wiki/index.php?plpgsqlfunctions

There is a function that given a point with a defined SRID (not -1) will
give you the SRID of the UTM zone for that point

2) http://spatialreference.org/

Has a plethora of options and search to find the spatial ref that works best
for you.

Hope that helps,
Regina

_____

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Joe
Roberts
Sent: Sunday, June 22, 2008 4:11 PM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Newbie - get total distance travelled from query
ofpoints

Hi,

I am very new to PostGIS, and I'm stuck with what I hope is an easy
problem to solve.

I have a table which contains a list of points, originating from a GPS
device's lat/long output. I want to get the distance travelled. I have
the following query, but the result (distance) looks far to low:

SELECT ST_Length(St_MakeLine(point))/1000 as distance

FROM (
SELECT point FROM points
ORDER BY timestamp
) as p

I know the route was over 5 miles (probably about about 8.4 km), but
the query returns 0.000106496.

Can anyone see what I am doing wrong? Is it my query, or could it be
my data?

Many thanks

Joe
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