circe

I'm starting to use the shareware version of OziExplorer to try it out. I'm
in the UK so I'm using an Great Britain Ordnance Survey map and have my
Garmin etrex venture set to the GB OS grid, and the GB OS map datum (Airy
Spheroid OSGB 1936).

The process I am going through at present is to scan in the area of the OS
map I require (1:50,000 landranger or 1:25,000 Explorer/Outdoor Leisure),
then straightening the scan in Photoshop. Next I'm entering a couple of
reference waypoints in my GPS that are to OS grid references of 1 km squares
at opposite ends of the map, for example SO/910810 and SO/930830.

Next run OziExplorer and download the reference waypoints from the GPS, open
the scanned map image, and use the waypoints to calibrate the map, before
setting waypoints along the walk I intend to make and re-transmitting them
back to the GPS. After my walk I open the saved map and download the
waypoints and tracks from the GPS.

I note however that the GPS unit only transfers data to and from the PC in
UTM and WS84 datum. The tracks in OziExplorer appear to line up rougthly
where I went.

I am aware that under normal circumstances using the wrong datum in the GPS
unit will create a small error, however I was wondering if I would get any
errors in OziExplorer because of this, or does the GPS unit handle all of
this internally? Also, if anybody has a better method I'm willing to hear.

Dave Patton

"circe" <circeTWOZEROZEROTWO@yahoo.co.uk> wrote in
news:cf32hr$1b3$1@titan.btinternet.com:

> I'm starting to use the shareware version of OziExplorer to try it
> out.

Best place for OziExplorer questions is the
OziExplorer Users mailing list:
http://groups.yahoo.com/group/OziUsers-L/

You should also take a look at my
OziExplorer Information page:
http://members.shaw.ca/davepatton/ozi/index.html

> I'm in the UK

As are a number of people on the Ozi Users list.

> and have my Garmin etrex venture

I also have a Venture. There is some Venture-specific
info on my GPS page in the "Newsgroup postings" section:
http://members.shaw.ca/davepatton/gps.html

> The process I am going through at present is to scan in the area of
> the OS map I require (1:50,000 landranger or 1:25,000 Explorer/Outdoor
> Leisure), then straightening the scan in Photoshop.

Be carefull with your scanning/correcting, as you could be
introducing problems for proper map calibration.
Also, I believe you are violating copyright law, because the
OSGB doesn't permit copying of the maps.

> Next I'm entering
> a couple of reference waypoints in my GPS that are to OS grid
> references of 1 km squares at opposite ends of the map, for example
> SO/910810 and SO/930830.
>
> Next run OziExplorer and download the reference waypoints from the
> GPS, open the scanned map image, and use the waypoints to calibrate
> the map

Needless extra setp to use the GPS. Just do a 'load and calibrate'
in Ozi, and enter the coordinates for the calibration points.
Two calibration points may not be enough for a good calibration.

> I note however that the GPS unit only transfers data to and from the
> PC in UTM and WS84 datum.

> I am aware that under normal circumstances using the wrong datum in
> the GPS unit will create a small error, however I was wondering if I
> would get any errors in OziExplorer because of this, or does the GPS
> unit handle all of this internally?

Garmin GPS receivers transfer data using WGS84, so that's what
you use in Ozi as the GPS upload/download datum.

--
Dave Patton
Canadian Coordinator, Degree Confluence Project
http://www.confluence.org/
My website: http://members.shaw.ca/davepatton/