[GRASS-user] Latitude/Longitude vs UTM

[Damiano G. Preatoni]

For the record:
not only norway has compensation zones in the UTM grid (so to stay in just one fuse) but also here in italy we have some regions (LAU2 units) that span across 32 and 33 and project all on 32.
As far as you don't exceed 2/300 km, IMHO you can extend into the adjacent fuse...
HTH
 --
Damiano G. Preatoni
UAGRA-DASS Università dell'Insubria
Via J.H. Dunant, 3
I 21100 Varese
[via mobile]

-original message-
Subject: Re: [GRASS-user] Latitude/Longitude vs UTM
From: Glynn Clements <glynn at gclements.plus.com>
Date: 2010-05-14 20:28


Dylan Beaudette wrote:

> >  There is a USGS technical report from the mid-1980s that's the standard on
> > projections. While it is becoming more rare to locatate, see if you can find
> > a copy.
> 
> I think that Rich is referring to this USGS document, #1395
> 
> http://pubs.er.usgs.gov/usgspubs/pp/pp1395
> 
> Definitely worth the price if you want to become an expert in map projections.

According to that page, it's no longer available in hardcopy; however,
you can download it as a PDF.

> >  Interesting. NH is a tall, narrow state so one would assume it would be
> > within a single zone. Regardless, yes there is a way to reproject locations
> > in one zone on the other, but it's non trivial and I've not done it.
> 
> I wouldn't recommend it. The desirable properties of the UTM system
> (i.e. the fairly good compromise between distortion, preservation of
> angles, and preservation of area) only occur within a zone's
> boundaries. The farther you move from the central meridian of the UTM
> zone, the more distortion you will encounter-- therefore 'projecting'
> UTM z10 data into UTM z11 is technically possible, but not a great
> idea.

That doesn't stop Norway doing it ;)

http://upload.wikimedia.org/wikipedia/commons/e/ed/Utm-zones.jpg

See 32V and 31X/33X/35X/37X.

The SW fragment of NH which is in zone 18 is only around half a
degree; projecting that into zone 19 isn't really an issue. Or you
could just use a custom transverse Mercator projection with the
central meridian at e.g. 71d30'W.

-- 
Glynn Clements <glynn at gclements.plus.com>
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