On 11/13/09 11:38 AM, "Grant Ingersoll" <gsing...@apache.org> wrote:
> If I implement Vincenty's formula for distance between two points on an > ellipsoid that can be accurate down to the 0.5mm. Not doing that yet and not > planning on implementing, so this is not a huge issue right now. > > Still, I think we should put it on our roadmap. +1 Cheers, Chris > > > On Nov 13, 2009, at 1:32 PM, Yonik Seeley wrote: > >> On Fri, Nov 13, 2009 at 1:01 PM, Walter Underwood <wun...@wunderwood.org> >> wrote: >>> Float is almost never good enough. The loss of precision is horrific. >> >> Are you saying it's not good enough for this case (the final answer of >> a relative distance calculation)? >> 7 digits of precision is enough to represent a distance across the US >> down to the meter... and points closer together would have higher >> precision of course. >> >> For storage of the points themselves, 32 bit floats may also often be >> enough (~2.4 meter resolution at the equator). Allowing doubles as an >> option would be nice too - but I expect that doubling the fieldcache >> may not be worth it for many. >> Actually, a 32 bit fixed point representation would have a lot more >> accuracy for this (256 times the resolution at the cost of on-the-fly >> conversion to a double for calculations). >> >> -Yonik >> http://www.lucidimagination.com > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Chris Mattmann, Ph.D. Senior Computer Scientist NASA Jet Propulsion Laboratory Pasadena, CA 91109 USA Office: 171-266B, Mailstop: 171-246 Email: chris.mattm...@jpl.nasa.gov WWW: http://sunset.usc.edu/~mattmann/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Adjunct Assistant Professor, Computer Science Department University of Southern California, Los Angeles, CA 90089 USA ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
