Oziexplorer error??

Submitted: Tuesday, Jun 10, 2003 at 11:44
ThreadID: 5374 Views:3250 Replies:4 FollowUps:1
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Hi all, here's one for all the Oziexplorer experts - I have both the Auslig 1:250k maps as well as the S.A. 1:50k maps on my laptop. Using moving map while on the move, the pointer always points nicely to the track/road, irrespective of which map set I run - in other words, it always appears accurate. However, if I plot a route prior to a trip using the 250k maps and then load it up on the 50k maps, it is out by around 200 - 300 metres. Conversely, if I plot the route on the 50k maps and then load the route on the 250k's, once again it is out. Now before you tell me to check the datum - if I check the datums (maps and GPS) one more time, I'll go spare! I suspect that Oxiexplorer somehow does not convert between the respective map datums like it says it does (the two map sets do use different datums) but I'm really not sure. I just seems odd that in moving map, the GPS plots accurately on either map set but manually plotted waypoints on one map set are always out when displayed on the other. Any suggestions or advice is gratefully accepted.

Cheers
Gerry
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Reply By: Member - Rohan K - Tuesday, Jun 10, 2003 at 12:54

Tuesday, Jun 10, 2003 at 12:54
Gerry, ask the same question at http://groups.yahoo.com/group/OziUsers-L/

There are plenty of experts there.

My understanding is that, depending on your GPS brand) Ozi transfers data to/from the GPS in WGS84 and will convert that the datum set by you in display. However, you do need to change that datum in display to suit the map you are using. In moving map, the GPS reads the position and then converts it to WGS84 when transferring it to Ozi and Ozi plots that on the map using the encoded datum, so it will always be accurate.

When you create your own points, you can do so in either the map datum, or any other datum you have set in the Ozi configuration menu. However, unless you match the display datum to the datum that you originally used when creating the points, you will get an error. The new Australian datum standard does, in fact, move points about 200 metre NE of GDA66 or GDA84.

I found constantly changing datums to match different maps too complex. Whenever I forgot, I'd get incorrect reading/placement. To avoid all these issues I have my GPS set to WGS84, and all Ozi settings in the configuration set to WGS84 and I leave the display datum at WGS84. That way, everything is always the same and I seem to get accurate results every time.
Talk is cheap ...
Rohan (Sydney)
AnswerID: 22196

Reply By: Guy - Tuesday, Jun 10, 2003 at 14:02

Tuesday, Jun 10, 2003 at 14:02
Before going into the details of Oziexplorer.
Where do you get the 1:50 electronic maps from? Any chance to emai me direct. at aufempen@modemss.brisnet.org.au as I am interested at getting some.

I had the same problem that you mentioned.
This had nothing to do with transfering waypoints from one type of map to an other but it was similar because I was correcting some of my data using Excel and *.csv. Then changing the file attribute accordingly to *.wpt or *.plt etc.

I asked the oziexplorer newsgroup about this particularity but no one understood what I was talking about. Instead the Oziexplorer newsgroup users had the impression that I was criticizing and denigrating Oziexplorer. Even Des Newman got onto the act.
I totally support Oziexplorer. I think it is a great product
I never got any logical answers from the newsgroup..

The answer to your question is this:
At the begining of each Oziexplorer, which is produced by different Oziexplorer
versions there is a text like this (open with Notepad)
OziExplorer Waypoint File Version 1.0
WGS84
Reserved 2
Reserved 3

and an other example with Track points or *.plt file
OziExplorer Track Point File Version 2.0
WGS84
Altitude in Feet
Reserved 3
0,2,8388736, new Road 1 , 0
50

The explanation is this.
Each different version of Oziexplorer look at this data files differently and will convert the waypoints or PLT points to whatever you have set up your Oziexplorer.
The conversion is automatic and you can NOT stop Oziexplorer from converting the file.
This error happen during the conversion because the conversion in my view round up the data to the nearest value.
Des so far has not given any explanation why the data needs to be converted each time a data file is loaded.
To which format is this data converted to. I would say this is converte to Des proprietary (secret) internal format. (to be able to use Des confidential algorithm).
When you see the speed at which the map is moved or displayed, something has to be truncated and approximate. Oziexplorer is very fast and still the accuracy is very acceptable.

I asked Des if it was possible to lock the conversion when under the same type of data and Des told me it was not possible.

But this is what I found by testing physically the waypoints. A drift North-East by 200 to 300 metres on the WGS84.
I found after doing a lot of conversion on the same data file, the drift stabilize it self and does not exceed 200 to 300 metres but change direction.
I think this type of Internal Oziexplorer algorithm is a form of mathematical attractor (Chaos-Mendelbrot etc..).
If you have an other explanation please let me know. I'll be interested.
Guy
AnswerID: 22204

Reply By: Member - Mike (SA) - Tuesday, Jun 10, 2003 at 14:39

Tuesday, Jun 10, 2003 at 14:39
Gerry, If it is any consolation - I too have this problem! I have put it down to the SA 1:50K topo which I have found very difficult to calibrate. In the end I took 4 Waypoints from the 1:250K and improved the alignment quite markedly over a small area. It was still way off at the other end of the map!
I have found my .PLT files to be 300 to 400 metres (Max) NE. I am rather disppointed with the SE Topo as the HEMA and Westprint maps, together vwith the NATMAP give me no trouble.
cheers
MikeToo little time in the bush!
AnswerID: 22208

Reply By: Eric from Cape York Connections - Tuesday, Jun 10, 2003 at 22:52

Tuesday, Jun 10, 2003 at 22:52
Whats it all mean It was easy before all the above just get a map and compass and go.
All the best Eric
www.capeyorkconnections.com.au
Eric 02 4294 3496
Pete 07 4094 1745Cape York Connections
AnswerID: 22265

Follow Up By: Member - Willem- Tuesday, Jun 10, 2003 at 23:58

Tuesday, Jun 10, 2003 at 23:58
Me too. All this stuff is way beyond me. I've got all the gear though. I find I really don't need it. A few weeks ago out in an isolated place in the North Flinders Ranges I pointed the map cursor over the place I was looking for for and then drove to approximately where it should be via the GPS reading and found it. A lot of people though want GPS readings for places which are marked on a map and easy to find by just looking!!
Some are even signposted...............
We traversed the Simpson Desert (north/south) in 1987 with a sextant, a compass and a calculator and some common sense :-)))) 550km of no tracks
Cheers, Willem
Never a dull moment
0
FollowupID: 14643

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