Decimal() instead of float?

Robert Kern robert.kern at
Sat Nov 18 01:33:43 CET 2006

Robert Kern wrote:
> Fredrik Lundh wrote:
>> Terry Reedy wrote:
>>> This is far more accurate than any measured latitude could be.
>> you're saying that we don't measure geographical positions on an atomic 
>> scale? ;-)
>> (it's too late for serious calculations, but I'd guess we're talking 
>> Ångströms here, right?)
> The meter was originally defined to be 1e-7 of the distance between the equator
> and the North pole, so 1 degree of latitude is roughly 1e7 m/90 ~ 1e5 m. 1e-16 *
> 1e5 = 1e-11, 1/10th of an Ångström.

Oops. Most of the latitude values will have 2 digits before the decimal point,
so in fact, we need 1e-14 deg * 1e5 m/deg = 1e-9 m or 10 Ångströms.

The quoted precision of the actual values that the OP used as examples is about
1e-7 deg * 1e5 m/deg = 1e-2 m.

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco

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