Calibrating OSGB Maps

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Scott
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Calibrating OSGB Maps

Postby Scott » Thu May 12, 2005 12:16 am

How do I calibrating my OSGB Maps?

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Scott
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Calibrating OSGB Maps

Postby Scott » Thu May 12, 2005 12:17 am

Most OSGB maps have horizontal and vertical OSGB Grid lines. PathAway Rectangular Calibration requires Longitude/Latitude lines to be horizontal/vertical. If this is the case for your OSGB map, you will need to either rotate the map so the Long/Lat lines are rectangular, or you will need to use a Projected map to Calibrate correctly. To calibrate OSGB maps such as this you can use the following projection parameters:

Calibration Type: Projection
Datum: OSGB
Projection: Transverse Mercator
lon_0: W2.000
lat_0: N49.00
x_0: 400000
y_0: -100000

Use at least 2 known points for the calibration points.

goon
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Postby goon » Wed Jun 07, 2006 8:51 pm

Is there any chance of a detailed step by step walkthrough for OSGB calibration (especially with relation to Memory Map screenshots :D :wink: ) I am getting fairly accurate and nudging once in the field, but I recently discovered that the coordinates reported by Pathaway differ from those reported by Cetus GPS.

Cheers,
Gareth Evans

esbark
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OSGB Calibration

Postby esbark » Wed Jul 12, 2006 6:32 pm

I asked this same question exactly one month ago and got no replies. Please , Please would any user in GB help us? Surely someone is managing to do this??? and could spare 5 minutes to post a few screen shots to help the rest of us. afterall if we cant calibrate the maps accurately the program is of no use.

TheSnake
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Location: S.England

Postby TheSnake » Fri Jul 14, 2006 2:16 pm

I am calibrating OSGB maps successfully, what specific problems are you having??

TS

esbark
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Calibration Of OSGB Maps

Postby esbark » Sat Jul 15, 2006 12:08 pm

Hello TheSnake,

I am just about to renew my efforts to use pathaway on my palm IIIX. I have been trialing gpspilot ATLAS for some time and its accuracy is spot on. It uses a map generator called "cartographer" which uses the common top left bottom right method of calibrating. Unfortunately using lat and long as references to calibrate drives me ( like many others in GB ) crazy. Atlas will not navigate using "track up" which is a feature which I want , hence my trials with pathaway. I have been watching your posts and had sussed out that you had sorted the accuracy thing out ( you were assisting The Goon I believe ) so i am very pleased to hear from you.
My original post of a month ago asked whether I should have a go using Touratech rather than map calibrator since i assume ( rightly or wrongly ) that it may be simpler ( after reading about all of the problems with calibrator ) . Since I did not have any replies I decided only yesterday to have a go with Touratech but have not quite started yet. Since I have now received your post I will stick with Mapmaker , since that is what I believe you are using. If you have experience of Touratech then perhaps you will say so. Anyway in answer to your question " what problems am I having ? " the answer is " none yet " since I am just about to begin. Reading about the experiences of others I expect the most daunting part of the whole procedure is the syntax of those "calibration points " and i see your mention of "using unique eastings" which I do not fully understand so I would greatly appreciate a screenshot of one of your maps showing these settings just before you hit the "export to palm " button if you would be kind enough.
Thank you again for your very timely response to my post

TheSnake
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Location: S.England

Postby TheSnake » Sat Jul 15, 2006 9:20 pm

Hi there,

If you download this PathAway Map...

http://pathaway.com/forum/download.php? ... 85e510bfec

...and load it into MapManager, it should give you a good idea what parameters, etc. to set up.

The reference to 'unique eastings' just means that all 4 of my calib.points are on different (unique?!) northings/eastings.

It's important to ensure that you enter the the Northings and Eastings correctly into MapManager, i.e for Grid ref SU430120 you need to enter these as:-

SU
12000
43000

(Note: Northing before Easting as these fields are normally used for Lat/Lon)

Also important are the PathAway Co-ordinate preferences on the Palm/PPC, where the map datum must be WGS84 and 'Use Current Map Datum' unchecked.

Good Luck!

PS: I'm afraid I don't use Touratech

esbark
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Calibration Of OSGB Maps

Postby esbark » Sun Jul 16, 2006 2:51 am

Thank you TheSnake "3 points skewed is the secret" I am on holiday next week but I will check it out on my return and let you know how I get on.

Cheers :lol: [/img]

esbark
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Location: STOKE ON TRENT

Calibrating OSGB Maps

Postby esbark » Tue Jul 25, 2006 11:55 pm

Well "The snake" I sent your test.prc map to the palm, made sure that the coordinates setting preferences were as you said. Datum = WGS84 , use current map datum unchecked. I then put my GPS12 into simulator mode and typed in a position which I knew would fall on an exact intersection of gridlines on your map and hey presto it was smack on. The question now is can I do it with my map??
So I calibrated a map by following your method and it nearly worked but not quite . when i set a position on my gps it showed up to the south east of the actual point on the map ( probably about 200m error ). Did you need to nudge your map settings at all on the palm or did it work first time by setting it like i did???

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

Postby TheSnake » Wed Jul 26, 2006 4:13 am

Sounds like your GPS12 is using the OSGB Datum, try setting it to WGS84 and then set a position.

No 'nudging' is necessary.

ts

esbark
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Calibrating OSGB Maps

Postby esbark » Wed Jul 26, 2006 1:32 pm

Thanks Snake. Actually Pathaway wont allow the GPS to use OSGB as its Datum, it gives out an " unacceptable datum " message . I naturally had the gps set to that initially but after seing that message I did as you say, set the GPS to WGS84. So that istnt the problem. Anyway my gps put my position onto your map spot on so it cant be the gps.

I will do it all again tomorrow evening with another map it must be me doing something. I think I will load your map into mapmaker, take a screenshot to convert it to a Jpeg then re-load it as a new map into mapmaker and copy your calibrations to the letter.

Will advise results

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

Calibrating OSGB Maps

Postby esbark » Fri Jul 28, 2006 2:06 am

well I had another go without success i am afraid. I did not do as I suggested by using the snakes map but instead I started with a brand new map and calibrated it projection-ord srvy grt britn-OSGB. the palm showed my position to be roughly 400 metres in error. I then calibrated the map again using lat/long etc and my position was correctly shown. I then used my gps to tell me the approximate error to be expected between OSGB32 and wgs84 positions and the answer was roughly of the same order ie 400metres.
I therefore conclude that since my GPS is set to download WGS84 positional information rather than OSGB information I cannot correct the error. Setting my GPS to OSGB brings up an "unsupported datum " error .
So I must give up, or calibrate maps using lat/long.
If anyone following this thread can offer any comments then they would be much appreciated. I still cant figure how you do it snake , sorry. [/list]

fergal_om
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Postby fergal_om » Fri Jul 28, 2006 12:48 pm

esbark,

did you try using wgs84 as your datum and OSGB as your grid coordinates when calibrating your map in map manager? I think this should work, we it does for irish grid anyways which in based on OSGB as far as i know

f

esbark
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Location: STOKE ON TRENT

Calibrating OSGB Maps

Postby esbark » Fri Jul 28, 2006 6:42 pm

Fergal_om,

No, I havn't tried that, I followed The Snakes way as I said. What you say makes sense. I concluded that I needed to shift the downloaded position at the GPS end. I suppose thats the same as shifting the datum at the mapping end as you do.

Will have another go

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

Postby TheSnake » Sat Jul 29, 2006 4:22 am

Very strange, if you've calibrated a map similar to test.prc and have WGS84 set as datum within PathAway, then logically it must be the GPS, as that setup works for me.

However, logically, what fergal_om says is correct too!

The OSGB instructions for MapManager definitely say Datum=OSGB though :?

Maybe I could calibrate a map for your area, so you could check it out.

ts


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