Ian Rainbow wrote:
Hi All,
On Sunday, 9th of February I took a GPS reading at the Rotunda of the
lake near La Trobe Uni. I presume this is Gresswell Lakes from the
reference to Gayle McDonald & the Little Bitterns. It was 37 deg 42
min 54 sec S, 145 deg 3 min 18 sec E in the Australian 84/86 system
from 5 satellites.
[snip]
A quick note about GPS coordinates.
The standard GPS datum is WGS84 (World Geodetic System '84.) Most
Australian maps use a different datum, Australian Geodetic Datum '66
or AGD '84. Using the wrong datum (WGS vs. AGD) results in an position
error of about 200m, so if you aren't using WGS84 with your GPS, be sure
to quote the datum used (as Ian has done.)
A new datum, GDA94 (Geodetic Datum of Australia '94) has been developed
which eliminates this problem, but will take time to replace AGD. All
of the maps I have use AGD66; I think the latest Melway has switched to
WGS84/GDA94 coordinates (probably thanks to the introduction of GPS
navigation systems in cars*.)
This AUSLIG page explains the differences in the data quite well,
considering the complicated mathematics involved:
http://www.auslig.gov.au/geodesy/datums/
* Here's a reason not to rely _too_ much on car GPS systems ;-)
http://catless.ncl.ac.uk/Risks/20.14.html#subj1
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Paul Taylor Veni, vidi, tici -
I came, I saw, I ticked.
Birding-Aus is on the Web at
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