Re: GPS Units and Railfans

[Neil Waller <nwaller@denr.sa.gov.au>]

Rolfe Bozier wrote:
> 
> 
> I've been thinking about picking up a GPS receiver at some stage for recording
> rail locations etc.  The main thing to bear in mind is that civilian receivers
> are only accurate to around 100m.  That may be fine if you're out in the middle
> of the countryside, but not much use for recording the details within a yard,
> for example.  The other thing you want to make sure of is that the unit will
> give you coordinates which are compatible with the maps you are using.  Most
> recent maps should be either in UTM/AGD84 or lat/long, which should be no
> problem.
> 
> If you're interested in general information on GPS, a couple of useful sites
> are:
> 
> http://www.utexas.edu/depts/grg/gcraft/notes/gps/gps.html
> http://deathstar.rutgers.edu/geom_class/GPS/GPS.html
> 
> Various manufacturers (e.g. Magellan, Garmin) will have details on their web
> sites.
> 
> I'm in the process of putting together a gazetteer of NSW railway locations, in
> lat/long coordinates.  If anyone is interested, let me know.  Eventually it'll
> be available along with some other data over the web.
> 

Will these coordinates be in AGD84 or GDA94?   GDA94 is the prefered
coordinate system and DEHAA's online cadastral data is now in that coordinate
system.

Our published topo maps will follow from this year.

A lot of other agencies will convert at the end of this year.

A GPS will give you coordinates that are earth centred rather than
based on a spheroid.   GDA94 is earth centred and is about 200m
different to AGD84.   Any UTM (AMG) coordinates will also be
different:   the appropriate UTM projection to use with GDA94 is
MGA, and with AGD66 and AGD84 AMG.   The transformation parameters
are slightly different and, all this being equal (which they are
not), lead to a differance of about 14 metres in the calculation.

A discussion on the Australian Geodesy can be found at
http://www.anzlic.org.au/icsm/icsmgeod.htm

You might also care to start at http://www.denr.sa.gov.au/ and
follow the links through Resource Information.


-- 
Neil Waller	(nwaller@denr.sa.gov.au)
Department for Environment Heritage and Aboriginal Affairs
Telephone:	Oz: (08) 8204 9218; International: (618) 8204 9218
Mail:		GPO Box 1047, ADELAIDE 5001     Australia

Unless explicitly attributed, the opinions expressed are personal
and not those of DEHAA or the South Australian Government.