[postgis-users] distance between two POINTM

[Paul Ramsey]

Excellent sleuthing Michael.  If you want to get consistent results  
between a GPS track and a point-to-point measurement, M. Welter,  
attach your GPS unit to a crow :)

P

On 13-May-07, at 3:52 PM, Michael Fuhr wrote:

> 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.