Re: distance on the equator by map project

Dear Takaya,

There are several reasons for that:

1) The earth is not a perfect sphere: the equator is longer than the sum of two meridians.  The original definition of 1 mile was to be 1 arcminute along a meridian, not the equator.

2) The definition of 1 mile has long since (1929) been modified to be an exact number of kilometers: 1852.

Regards,
Remko

On 13 Mar 2014, at 22:19, Namba Takaya <[email protected]> wrote:

> Dear Sir
> 
> I tried to calculate the distance on the equator to check the result of mapproject as
> 
>  lon=2
>  lat=0
>  lonn=3
>  latn=0
>  echo $lon $lat |mapproject -f0x,1y -G$lonn/$latn/n 
> 
> and the result is
> 2       0       60.0405398135.
> 
> My question is why it is not 60.0000 nautical miles exactly?
> 
> regards,
> 
> takaya

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