Calibrating OSGB Maps

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esbark
Posts: 24
Joined: Mon Jun 12, 2006 7:24 pm
Location: STOKE ON TRENT

Calibrating OSGB Maps

Postby esbark » Sun Jul 30, 2006 11:11 am

Well I am afraid that I am going to have to give up on Pathaway. I still cant crack it and really need to progress. I calibrated my local map set as Fergal_om suggested with the same results as before. My position on the map is 400metres south of where it should be.
My map is cropped at grid intersections and calibrated on all 4 corners Top left is SJ79000 59000,Top right is SJ90000 59000, Bottom left is SJ79000 51000 bottom right is SJ 90000 510000. Gps is set to WGS84.
I attach it and await your comments The Snake
Attachments
TRIAL2.prc
(883.89 KiB) Downloaded 1266 times

esbark
Posts: 24
Joined: Mon Jun 12, 2006 7:24 pm
Location: STOKE ON TRENT

Calibrating OSGB Maps

Postby esbark » Sun Jul 30, 2006 11:27 am

Further Info.

I took the gps outside ( instead of using it in simulator mode ) and with it set to wgs84 my position WAS much closer to where it should be . I then altered the gps to output as OSGB and the map moved to show my correct position just for a few microseconds before Pathaway informed my that OSGB was an unsupported datum and that it would be disconnected. So I nearly got there but need the program to be able to download with GPS set to OSGB

TheSnake
Posts: 44
Joined: Mon Mar 27, 2006 2:43 am
Location: S.England

Postby TheSnake » Mon Jul 31, 2006 6:11 pm

Now's not the time to give in!

Let's try and nail this on the head before you get any more disheartened.

Lets take the GPS out of the equation, and do a quick test.

I've uploaded a point database containing 1 point for you to import. This point is exactly on SJ 80000 58000 and was defined using WGS84 Lat/Lon in DD.dddd format. You'll need to change the extension from .txt to .pwpts as I couldn't upload that kind of file.

Create a TRIAL3 calibrated map - from TRIAL2, using exactly the same details but 'Ord Srvy Gt.Brit' as Datum, and load both onto your Palm.

This brings me to my first question. Have you been trying to get this to work with more than 1 map of the same area loaded on your Palm with different datums?? If so - this could cause all manner of problems. For this test I switched on/off the TRIAL2/TRIAL3 maps using the Maps checkboxes to ensure only one was available at any one time.

Then follow these steps...

1. GPS NOT connected!
2. Show point 'trial' from xMy Points database.
3. Using TRIAL2 map, the point should always be positioned to the NW of SJ8058 no matter what PathAway is set to on the Co-ordinates preference page.
4. Using TRIAL3 map, the point sould always be positioned dead on SJ8058 no matter what PathAway is set to on the Co-ordinates preference page.

For example:
Goto Preferences...|Coordinates, and for 'Primary Coordinates', set the Position to DD MM.mmm. Either set 'Use current map datum' OR select 'Ord Srvy Gt.Brit' from the Datum dropdown list. The Lat/Lon displayed at on the dashboard will be N53 07.266 W2 17.808 - these are the OSGB lat/lon values (like you'll find on the border of any OS map)
As above but unset 'Use Current Map datum' and select 'WGS84' from the Datum dropdown list. The Lat/Lon displayed at on the dashboard will be N53 07.282 W2 17.894 - these are the WGS84 lat/lon values (like you'll find say on a Geocache page)

If you get the same Lat/Lon values as those above, then at least the Map/PathAway combo is working, and we can concentrate on getting the GPS working with the rest! At which point the next question will be: 'What protocol do you have selected under GPS configuration?'

ts
Attachments
xMy Points.txt
(60 Bytes) Downloaded 1348 times

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Scott
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Postby Scott » Mon Jul 31, 2006 6:31 pm

It is correct that a 400m difference means the map may have been calibrated using WGS84 datum instead of OSGB.

Some tips:
- Internally PathAway operates in WGS84. If data is coming from the GPS in WGS84 then the coordinates are converted to the Current Datum for display on the screen. It doesn't matter what Datum your GPS is set to. PathAway will internally convert it to WGS84 no matter what the GPS spits out. So it's always more efficient to set the GPS device to WGS84.

- If you want to use captured points from the GPS to calibrate in OSGB coordinates, then go into your Preferences->Coordinates and set your Primary Coordinates to OSGB, make sure to turn OFF "Use Datum of Current Map" because the map may not be in OSGB yet, and select the "Ord Svy Grt Brtn" Datum. It may be that the "Current Map" is in WGS84 so if "Use current map datum" is on then the coordinates may be in WGS84. This is the case with the "Virtual" map because it's default datum is WGS84.

- To calibrate the OSGB map in Map Manager from the gridlines on the OSGB map, you must set Coordinates to OSGB and Datum to "Ord Svy Grt Brtn".

I hope some of this helps.

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Scott
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Postby Scott » Mon Jul 31, 2006 6:53 pm

I editted ESBARK's trial2.prc, (see attachment) so it uses "Ord Svy Grt Brt" datum and the map now appears to be right on. It should work with the GPS as long as it is set to output WGS84 datum.
Attachments
TRIAL2Scott.prc
Fixed map set to use OSGB datum.
(883.89 KiB) Downloaded 1490 times

esbark
Posts: 24
Joined: Mon Jun 12, 2006 7:24 pm
Location: STOKE ON TRENT

Postby esbark » Tue Aug 01, 2006 1:41 am

':lol:'':lol:'':lol:'':lol:'

Thank you The Snake and Scott,

I can now do it. Firstly I learned that I must no longer set the GPS to simulate my position as a means of checking the software , It must be done live in the field ( or in my garden) with the Gps set to WGS84
Scotts Explanation of the preferences for the coordinates helped a lot ( I had the datum set to WGS84)

The snakes point also enabled me to check calibration another way to replace the gps in simulator mode.

So thank you all, now that I am navigating accurately I can check out the other points in Pathaway.

I am attaching a jpg of my palm screen to clarify those calibration settings for other interested users ':lol:'':lol:'':lol:' ESBARK
Attachments
Pathaway Coordinates.jpg
Pathaway Coordinates.jpg (13.27 KiB) Viewed 21515 times

TheSnake
Posts: 44
Joined: Mon Mar 27, 2006 2:43 am
Location: S.England

Postby TheSnake » Tue Aug 01, 2006 9:19 pm

Glad you got it working in the end!

ts


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