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From Grant Ingersoll <>
Subject Re: Functions, floats and doubles
Date Fri, 13 Nov 2009 18:38:58 GMT
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. 

On Nov 13, 2009, at 1:32 PM, Yonik Seeley wrote:

> On Fri, Nov 13, 2009 at 1:01 PM, Walter Underwood <> 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

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