Re: OziExplorer and Datums
From: Mark Zak (markzak_at_barzak.com)
Date: 12/27/04
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Date: Mon, 27 Dec 2004 11:15:05 GMT
Bill and Andrew,
Thank you both for your responses.
The area in question is Port Phillip Bay (AUS143, AUS 157 and AUS 158). The
scanned charts are in AGD 66 datum. BlueCharts and GPS are set to WGS 84 and
OziExplorer 'Map Datum' is set to AGD 66.
I navigated my routes using BlueCharts and I am happy with the accuracy.
However, when dowloaded the routes from GPS to OziExplorer, they are not
exactly the same which can be disastrous in southern part of Port Phillip.
Also noticed BlueCharts do not show the sounding detail the marine charts
do, i.e., there are some areas with waters only 0.30m depth which do not
show on BlueChart even with 'map detail set to highest'
I have checked, rechecked and once again re-checked map calibrations and I
am confident the problem is not there.
I am fairly comfortable with the basics of datums and marine charts and do
not know what I am doing wrong but will pursue and once again many thanks
for your responses
Mark Zak
"Andrew" <andrewdotsander@bigpond.com> wrote in message
news:Z%Gzd.89218$K7.28449@news-server.bigpond.net.au...
>
> "Mark Zak" <markzak@barzak.com> wrote in message
> news:O3Azd.89104$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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