[postgis-users] distance between two POINTM

[Michael Fuhr]

On Sun, May 13, 2007 at 04:15:39PM -0600, Michael Welter wrote:
> Michael Fuhr wrote:
> > These points appear to be along US285 in the vicinity of Conifer, CO.
> > Might your GPS be measuring driving distance instead of straight-line
> > distance?
>
> Correct, but driving distance doesn't account for the 700m discrepancy.

Why not?  The straight-line distance from distance_sphere() is
4479m, or about 4.5km as you said.  But the highway between those
points (Aspen Park and Broken Arrow Acres, right?) isn't straight,
and when I measure the segments of US285 between the points using
data from CDOT I get 5252m, and the segments I'm measuring extend
slightly beyond the two points.  See the attached image: the distance
I measured as 5252m is the highway shown in red; take out the parts
that extend past the points and 5.2km is just about dead-on.

-- 
Michael Fuhr
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