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 _______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
