Float is often OK until you try and use it for further calculation. Maybe it is good enough for printing out distance, but maybe not for further use.
wunder On Nov 13, 2009, at 10:32 AM, 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 >
