[Proj] Distance between pair of lat / lons

[support.mn at elisanet.fi]

Hello,

yes, but what a distance?

If you are considering short distances where the most accuracy is usually
required (when building something up to ocean shpis) they do not need
any ellipsoids but straight lines from point to point (and maybe additionally
use lasers to verify them) and if you just give them arcs of accuracy nm you
might be totally in a wrong ball park?

So one needs at least two (or more) distances:

1) Straight line
2) Earth ellipsoidal length which can compensate for different heights above it
3) Some length that does not compensate for any elevations (this might be the
one you have been used to use)
4) A length that follows the earth surface curvatures
5) Maybe some more definitions for some applications

An additional point is that most users do not know their accurate elevation
above any ellipsoid but above the geoid (or some local MSL) so that will
add additional variables to the formula.

So to tell the actual distance between two lat/lons in nm region is not so
simple problem - or the answer is anyway wrong (since the question is
not accurate enough).

Janne.

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Jayesh Chaudhary [aashishcy at gmail.com] kirjoitti: 
> Folks,
> 
> We have been using GeoographicLib and it had a convenient function to
> calculate distance between two points with an error in the range of nm. I
> am familiar with PROJ4 but I don't see any such function in PROJ4. We do
> care about accuracy and therefore I am not willing to use simple methods
> that consider earth as perfect to compute such distance.
> 
> Please let me know if there is such functionality exists in PROJ4.
> 
> Thanks
> 
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