Joe Roberts wrote:
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
So assuming your GOS is return LAT, LON in WGS84
ST_Length is returning the length in degrees (IE: the Cartesian distance
in the units of the geometry) and that return 0.106496 degrees. If you
want miles you can multiple that by the number of miles/degree and
assuming a great circle like path there are approximate 69.172 miles per
degree along the Equator so you distance is 7.366541312 miles which
seems to fit with your statements above.
http://www.google.com/search?hl=en&q=miles+per+degree&btnG=Google+Search
-Steve
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