[postgis-users] Please post - Bounding box

[Bryce L Nordgren]

postgis-users-bounces at postgis.refractions.net wrote on 07/20/2011 08:00:02 
PM:

> 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

decimetre
centimetre
millimetre
100 micrometre
10 micrometre
micrometre
100 nanometre
etc.

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 
point stands.

A proper error propagation is required to determine the precision of the 
answer. :) 

Bryce
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