[Proj] Problems with /Op option used to compile proj in Microsoft Visual Studio

Glynn Clements glynn at gclements.plus.com
Thu Mar 15 23:59:10 EST 2012

Calogero Mauceri wrote:

> > Ultimately, I suspect that the calculation for the two-point
> > equidistant projection just wasn't designed for the case where the two
> > points are around one arc-second apart (approx. 15 metres; would be
> > approx. 40 metres on Earth).
> Glynn, so you are suggesting that more than in the float number 
> approximations, the problem is in why the number passed to the aacos is 
> so close to 1.
> Well, then my question is, which are the cases where the two point 
> equidistant projection could not behave well? Is it a problem of the two 
> point equidistant definition or a problem of the way it is implemented 
> in proj lib?

It's presumably possible to reformulate the calculation to be more
numerically stable, the question is whether it's worthwhile. AFAICT,
the projection seems to be more common at larger scales.

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