[gdal-dev] Ellipsoidal length of a line

[a.furieri at lqt.it]

On Mon, 17 Jun 2019 09:46:20 +1200, Mike Taves wrote:
> I'm not sure how SpatiaLite has implemented ST_Length,
> but could be worth checking into.
>
>

Hi Mike,

SpatiaLite started supporting geodesic distances
about ten years ago, and two different methods
were implemented as internal C functions:
1. the first was based on the Great Circle distance
    formula as reported by Aviation Formulary [1]
2. the second was based on the Vincenty inverse
    formula for ellipsoids as reported by a
    JavaScript implementation developed by Chris
    Veness [2]

In more recent times PROJ 4.9.0 started supporting
geodesic distances, so the situation became as follows:
- when libspatialite is built by defining "--enable-proj"
   (default setting) and PROJ >= 4.9.0 is available, then
   geodesic distances will be based on PROJ support.
- if not, the old internal implementation will be used.

bye Sandro (SpatiaLite developer)

[1] https://edwilliams.org/avform.htm#Dist
[2] http://www.movable-type.co.uk/scripts/latlong-vincenty.html