Dear Bob, Yes I realise this. However I have also heard from Oliver that the error is over 150 metres, so there is something much more fundamental. I suspect maybe the projection or datum has been set incorrectly when the data was loaded.
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] -----Original Message----- From: bob young [mailto:[EMAIL PROTECTED] Sent: 15 November 2005 12:53 To: [EMAIL PROTECTED] Cc: [email protected] Subject: Re: [Mapinfo-l] FW: GPS Geotrack and British National Grid Hi Tim I absolutely agree that MapInfo has got great features for reprojecting. However the method you outline will only position a user within about five or six metres of where they really are. With low cost GPS, the GPS psoition too will only be within 3 to 10 metres but the combined affect is a bigger error, as the two sets of errors are for different reasons. If a user has more accurate GPS, and there are a few sub metre solutions around, then the solution you propose, which will not include OSTN02 correction will not be good enough for the investment made in the GPS. The OSTN02 corrections ( see GPS.GOV.UK ) will give corrections to three decimal places of a metre. With the very accurate GPS systems available this accuracy is a requirement. It is fairly easy to prove this. You can draw in some lines with chosen lat long, then use MapInfo to reproject as you suggest, and note down the Easting, Northing MapInfo computed. Now submit the same lat, longs to GPS.GOV.UK and you will see you get values fve or six metres different. The reason for this is that MapInfo uses a mathematical model to move from one system to another. British National Grid as used in MasterMap has been based on County Series Maps and the only way to adjust to these from WGS84 is to use the published figures which Ordnance Survey have kindly made available free of charge for use by developers and users on their website. Regards Bob Tim Rideout <[EMAIL PROTECTED]> writes > >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: [email protected] >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 > >_______________________________________________ >Mapinfo-l mailing list >[email protected] >http://www.directionsmag.com/mailman/listinfo/mapinfo-l -- bob young _______________________________________________ Mapinfo-l mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l
