Hi David, I deal with conversions between WGS 84 and BNG in this area quite frequently and this is a well known problem. As I understand it these errors stem from the fact that in the original survey of the UK in 17**? there were small errors and when these were discovered in later surveys the error was "averaged" out over the whole of the UK. So at the grid origin the error would be 0m and in Shetland the error is about 24m. So in the middle of Scotland the error is about 12m.
The way OS suggest we correct it is to apply a different transformation based on where you are in the UK. As far as I'm aware Mapinfo can't do this. Check out the OS website for more details. I have downloaded "A guide to coordinate systems in Great Britain" This is not practical for me so i just don't use BNG if at all possible. Perhaps someone from OS could shed some more light on the subject? Jim Wilson Hilton of Fern, Brechin. Angus, Scotland www.soilessentials.com > -----Original Message----- > From: John Williams [mailto:[EMAIL PROTECTED] > Sent: 28 October, 2003 10:37 AM > To: Eagle, David A; [EMAIL PROTECTED] > Subject: RE: MI-L Off topic GPS Question - Scotland > > > David > > How did you convert the Lat/Long to British National Grid for each survey? > Do you have access to the original NMEA strings or just the Lat/Long > generated from the GPS? > > > John Williams > HandyGIS > Tel: 07050 398200 > Fax: 07050 398100 > www.handygis.com > > > > > -----Original Message----- > From: Eagle, David A [mailto:[EMAIL PROTECTED] > Sent: 28 October 2003 10:29 > To: [EMAIL PROTECTED] > Subject: MI-L Off topic GPS Question - Scotland > > > This is a vague question because I have very vague information at > the moment > and its posed at those of you who deal with GPS surveying...The > surveys I am > questioning are in Scotland, Uk. > > Situation: A vehicle survey with GPS tracking its position has > been done in > the Central Belt of Scotland (Glasgow, Edinburgh region) and the returned > results when converted from Lat/Long to BNG were spot on. A similar survey > further north near Dundee produced converted BNG coords with a southerly > 10-15m error. Then moving further north still to a point near Aberdeen the > coords are out to the south by 15-20m. > > The errors are consistent and seem progressive as you move north. > > My question to the masses is, how would you explain this and what > would you > do about it? I don't expect miracles as I haven't provided much technical > detail... > > I am inclined to believe some sort of calibration may have been > done in the > south and not altered for the two northerly surveys...is there any way of > checking in the NMEA message string whether the data is being corrected > differentially? > > Any thoughts greatly appreciated...sorry about the sketchy info, its being > fed to me slowly. > > Best Regards, David > > > > This email and any attached files are confidential and copyright > protected. > If you are not the addressee, any dissemination of this communication is > strictly prohibited. Unless otherwise expressly agreed in writing, nothing > stated in this communication shall be legally binding. > > > > --------------------------------------------------------------------- > List hosting provided by Directions Magazine | www.directionsmag.com | > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > Message number: 8902 > > > > > --------------------------------------------------------------------- > List hosting provided by Directions Magazine | www.directionsmag.com | > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > Message number: 8903 > > > --- > Incoming mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.522 / Virus Database: 320 - Release Date: 29-Sep-03 > --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.522 / Virus Database: 320 - Release Date: 29-Sep-03 --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 8909
