Re: OziExplorer and Datums

From: Andrew (andrewdotsander_at_bigpond.com)
Date: 12/26/04 

Date: Sun, 26 Dec 2004 22:34:33 GMT

"Mark Zak" <markzak@barzak.com> wrote in message
news:O3Azd.89104$K7.58351@news-server.bigpond.net.au...
> Hi,
>
> I have waypoints and routes ploted using BlueChart Pacific which I
> downloaded to GPSMAP276C and used in navigation. Both the GPS and
BlueChart
> Pacific were set to WGS 84.
>
> The scanned marine charts for OziExplorer are calibrated and set for their
> correct datum (AGD 66). However, when using the GPS (in simulation mode
and
> laptop) with OziExplorer 'Moving Maps' the route track is not the same as
in
> BlueChart Pacific for the same area. The track is dangeroulsy outside the
> channel/s.
>
> The GPS was set for "Map Datum" AGD 66 to match the marine chart datum. I
> later swithched the datums (WGS84 vis AGD66) on both the GPS and
OziExplorer
> in all possible combinations but this did not make any difference.
>
> Should I plan routes and plot waypoints usnig the scanned marine charts
> (published by offical hydrographic service) on the premise they are more
> accurate and upload to the GPS rather than using BlueCHart Pacific? Am I
> doing something else wrong?
>
> Thanking in anticipation for your help
> Regards
> Mark Zak
>

Mark,

What is the area we are talking about?

The bluecharts will be correct therefore i would be checking your
calibration of the scanned maps. Changing the datum (in GPS and Ozi) does
not necessarily do anything to the data, just what "numbers" are displayed.

To change the "map datum" in ozi, go to "check map calibration" and change
the datum from there. The waypoints and tracks will now be in a new map
location (approx 200m), though their coordinates would not have changed..

BTW most marine charts for AU have been georeferenced using the WGS84 datum,
therefore there should be no need to worry about AGD66 etc.....

Regards

Andrew

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