[postgis-users] Please post - Bounding box
Bryce L Nordgren
bnordgren at fs.fed.us
Wed Jul 20 14:35:45 PDT 2011
postgis-users-bounces at postgis.refractions.net wrote on 07/20/2011 08:00:02
> As I tell my students the precision is purely spurious. Geometry is
> stored as double precision values as far as I know but after the
> first few decimal places you soon get beyond what is measurable by
> modern survey instruments so I wouldn't worry about it.
> If you take a UTM zone measurement in metres at 4240000.5555555, the
> values after the decimal point are
> decimetre, centimetre, millimetre, micrometre, nanonmetre, picometre.
> A picometre is 1?10?12 m - you need about 100 or more to measure an
> atom. Obviously with Lat/Lon you are using an angular measurement
> but the same concept applies.
I agree with the principle but disagree with the details. :) After the
decimal you have
430-450 nm is roughly the wavelength of blue light. The "5" in the last
decimal place is "500 nm", which is green (more or less). Still, your
A proper error propagation is required to determine the precision of the
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