On Thu, Jun 11, 2015 at 01:52:02PM -0700, Linus Torvalds wrote: > On Thu, Jun 11, 2015 at 11:53 AM, Dirk Hohndel <[email protected]> wrote: > > > > QtPositioning is new - I use that to quickly calculate distances between > > GPS locations. > > Umm. Is that the only thing you use it for?
Umm, right now, yet. > Because if it is, it's kind of wasteful. > > The thing is, you only care about distances when they are near each > other, at which point the surface of the earth can pretty much be > considered flat. > > Which means that you can just calculate the distance in the > north-south direction, which is trivial: > > earthradius * (difference in latitude in radians) > > and the distance in east-west direction: > > earthradius * (difference in longitude in radians) * cos(latitude) > > and then - because you can approximate all relevant distances as being > euclidian - you just get the usual d = sqrt(x*x+y*y) and you're done. > > No silly new libraries needed. Ok, so I'm lazy. What else is new. > Now, if we care about distances on a bigger scale, that would be > different. But I guess the "distance" you are calculating is the one > where you then compare it to "20m or less"? Yes. > Yeah, the earth really *is* flat at those kinds of scales. Unless you > want to take wave height etc into account. not really. /C _______________________________________________ subsurface mailing list [email protected] http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface
