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

[Paragon Corporation]

Joe,
You need to convert to some sort of foot or meter projection that is
suitable for your area of interest.  your measures are in degrees.
 
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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