[Qgis-user] degrees: is degr/min/sec still used? Or decimal preferable?

[Bo Victor Thomsen]

I don't think the problems with accuracy stem from the limited number of 
decimals in a /double/ variable

  * The circumference of earth: ca. 40.076 km.

  * 1 degree in meters 40076 km / 360 = 111.32 km/degree = 111320 m/degree.
    

  * A double has 52 bits precision, roughly 15 digits (in 10 exponent).
    That means that the decimal degree has a precision of around
    111320/1000000000000000  = 1.1132e-10 m = (ca.) 1e-7 mm.
    (That should be enough for everyone...)
    

  * However, if you store your decimal degree value as a single
    precision real with 23 bits precision (aka. 7 digits precision in 10
    exponent), it's another story:
    This will give you around: 111320/10000000 m = 0.011132 m = 11.132 mm


So store your decimal degree as doubles, not single precision real.

Regards
Bo Victor Thomsen
Municipality of Frederikssund, Denmark



Den 10/04/17 kl. 08:39 skrev Richard Duivenvoorde:
> Hi List,
>
> Had a discussion here with some people about the use of showing the
> latlon degrees in degrees/minute/seconds tuple instead of the decimal
> notation:
> "4.40069397,51.71060887"
> vs
> "4°24′02.49807059″E,51°42′38.19184916″N" (or variations on that)
>
> Is there some general preference in this? To me the first one is just
> easier to handle, but I'm not sure what the general preference is in the
> GIS world.
>
> Any comments?
>
> Or is everybody using the national crs's anyway :-)
>
> Regards,
>
> Richard Duivenvoorde
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