HI Oliver
I think I did understand your question. These differences are due to the lack of OSTN02 correction. The correction you need to apply varies from each 1 km square to the next but is typically 110 metres in Easting AND 70 metres in Northing giving a typical diagonal error of about 120 metres. You cannot use a formula to apply this correction. You need to use the table supplied by Ordnance Survey and this is what we have built in to Maps4Site. The position we plot is within 3 to 5 metres with a £60 GPS. This error is down to the GPS. The correction applied is to the millimetre but of course this accuracy is only relevant when using 20 millimetre GPS which still costs thousands to implement. Regards Bob Oliver Francis <[EMAIL PROTECTED]> writes > >Dear Tim, > > > > > >Thank you for your comments. > > > >I don't believe I explained my problem correctly though. > > > >Once I have GeoTrack up and running with my GPS antenna, it locates me >around 120m away from where I actually am (I was expecting an accuracy >of 15m or so). When I move around, it is continuously 120m (WNW) of >where it should be. > > > >The problem I think I have is that the datum I am using (OSGB 36) is not >the same as the Datum GeoTrack is using to plot its position. > > > > > >Hope this makes more sense. > > > >Thanks > > > > > > > >Oliver Francis > > > > > >GIS Operator > >Maidstone Borough Council > >------------------------------------- > >I.T. Block B > >13 Tonbridge Road > >Maidstone > >ME16 8HG > >UK > >------------------------------------- > >tel: + 44 (0)1622 602438 > >[EMAIL PROTECTED] > ><http://www.digitalmaidstone.co.uk/> > > > >-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Tim >Rideout >Sent: 15 November 2005 11:36 >To: mapinfo-l@lists.directionsmag.com >Subject: [Mapinfo-l] FW: GPS Geotrack and British National Grid > > > > > >Dear Oliver, > > > >I don't see what the problem is. Import the stuff into MapInfo as >decimal degrees in Lat / Long WGS 84. MapInfo will then automatically >reproject your data on the fly into GB National Grid if you simply add >the GPS tab file into your National Grid map window. You can use the >'Save As' and click the projection button if you want to permanently >convert it to GB National Grid. > > > >It is one of the things about MapInfo and the Tab format. All tables >must declare their projection parameters so MapInfo always knows what >these are for any particular table. Thus for any map window it can >detect the projection used in that window, the incoming projection for >any table you are trying to add to that window, and thus arrange for the >automatic reprojection for display purposes. You don't even need to >think about it - it just happens. > > > >Try that in ArcView 3! > > > >If anyone isn't sure they know everything about MapInfo that they would >like to know, then you are welcome to look at our training course >outline and particulars at www.xyzmaps.com. The prices are pretty >reasonable and we cover a lot of ground. > > > >regards > > > >Tim > > > >Dr Tim Rideout > >Director > > > >Visit XYZ at the AGI Scotland Event in Edinburgh on December 1st. > > > >The XYZ Digital Map Company > >Unit 9 Phase 2 Hardengreen Business Park > >Dalhousie Road > >Dalkeith Scotland EH22 3NX > >Tel +44 131 454 0426 > >Fax +44 131 454 0443 > >Mobile + 44 7766 825937 > >E-mail [EMAIL PROTECTED] > > > > > >________________________________ > >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Oliver >Francis >Sent: 15 November 2005 09:23 >To: mapinfo-l@lists.directionsmag.com >Subject: [Norton AntiSpam] [Mapinfo-l] GPS Geotrack and British National >Grid > >Hello all, > > > > > >We have recently acquired 2 GPS antenna (Fortuna U2) that we intend on >using with our toughbooks whilst carrying out fieldwork. > > > >I have managed to get them up and running in MapInfo 7.8 Pro using >GeoTrack. The problem however is that our maps are based on British >National Grid. I've checked the online discussion group (Blue Marble >Geographics) and found that it is not possible to display GPS data in >Northings and Eastings. > > > >Can anyone think of a possible solution to my problem? > > > >Many thanks > > > > > > > >Oliver Francis > > > > > >GIS Operator > >Maidstone Borough Council > >------------------------------------- > >I.T. Block B > >13 Tonbridge Road > >Maidstone > >ME16 8HG > >UK > >------------------------------------- > >tel: + 44 (0)1622 602438 > >[EMAIL PROTECTED] > ><http://www.digitalmaidstone.co.uk/> > > > > > >Please complete our online survey and help us to improve our services to >you: > >http://www.digitalmaidstone.co.uk/customersurvey/ > >This email is confidential. If you receive it by mistake, please advise >the sender by email immediately. Any >unauthorised use of the message or attachments is prohibited. Unless >stated otherwise, any opinions are personal >and cannot be attributed to Maidstone Borough Council. This email is not >a contract or an order. It is your >responsibility to carry out virus checks before opening any attachment. > >www.digitalmaidstone.co.uk > > > > > >Please complete our online survey and help us to improve our services to you: > >http://www.digitalmaidstone.co.uk/customersurvey/ > >This email is confidential. If you receive it by mistake, please advise the >sender by email immediately. Any >unauthorised use of the message or attachments is prohibited. Unless stated >otherwise, any opinions are personal >and cannot be attributed to Maidstone Borough Council. This email is not a >contract or an order. It is your >responsibility to carry out virus checks before opening any attachment. > >www.digitalmaidstone.co.uk_______________________________________________ >Mapinfo-l mailing list >Mapinfo-l@lists.directionsmag.com >http://www.directionsmag.com/mailman/listinfo/mapinfo-l -- bob young _______________________________________________ Mapinfo-l mailing list Mapinfo-l@lists.directionsmag.com http://www.directionsmag.com/mailman/listinfo/mapinfo-l
