I have run into the bounds being an issue once or twice. It does not have anything to do with the projection, but is simply a function of the computing environment.
I am not sure if MapInfo works in 32 bit or 64 bit or whether this depends on the OS, however the result is basically the same. In theory MapInfo operates on an infinite white canvas so you can draw forever. In practice this is actually limited by a bounds setting. Usually the bounds are large - typically for a GB National Grid table it might run between -7,000,000 metres and + 7,000,000 metres. So you could digitise Iran into the table but not Japan (more than 7000 km away from GB). Roughly speaking 16 bits gets you four significant digits, 32 bits gets you 8 and 64 bits gets you 16. So if the environment is 32 bits then with bounds as above MapInfo could only hold co-ordinates to about the nearest metre in terms of accuracy. There are no digits left over for the decimal places as they are all used to the left of the decimal place. Any centimetres will be rounded off. I have seen this with someone digitising on OS Mastermap and carefully snapping everything together, then looking the next day and finding the new lines had all apparently moved 50cm or so away from the Mastermap points. The solution is to make the bounds smaller which then allows more of the digits to be used for the decimal places and therefore you can have better accuracy. Hope this helps, Tim Dr Tim Rideout Director Visit XYZ at the Cape Town International Book Fair, June 2006, Frankfurt Book Fair, Oct 2006, Intergeo Munich Oct 2006 or IMTA World in Singapore, Nov 2006. 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Payne Denis Sent: 05 July 2006 08:10 To: [email protected]; [EMAIL PROTECTED] Subject: [MI-L] Re: Changing the Bounds Clause You said: Date: Tue, 4 Jul 2006 17:10:29 +0100 From: "John Eyre" <[EMAIL PROTECTED]> Subject: [MI-L] Changing the bounds clause To: "MapInfo" <[email protected]> Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset="iso-8859-1" I've already had help with this problem but clearly not enough! First the problem. I am using 1:10,000 Ordnance Survey maps and overlaying these with site outlines. When I open the site outline table, the detail on the underlying OS map goes into square blocks. I have been advised that this is because the coordinate system of the OS map window is being limited by the bounds of the site layer. To correct this, I have to change the bounds of the site layer so that it doesn't control the spatial granularity of the OS Map. I need help in actually doing this! Can anyone spell out in layman's terms how I go about it? Many thanks. John ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- You need to save a copy of your original table - File Save As - that allows you to change the projection. The standard British National Grid projection covers the whole world, so should be good enough. If you're using version 8, then there's the 1mm accuracy option, if you wish. My guess is, though, that its a different projection rather than different bounds. You can look (using a text editor) at the tab file defining your rasters, the whole earth national grid has a line : CoordSys Earth Projection 8, 79, "m", -2, 49, 0.9996012717, 400000, -100000 And you can use the tool "Table Manager" to look at the projection information for any of your tables. Hope that helps Denis _________________________ Denis W Payne GIS Manager Cambridgeshire County Council Tel: 01223 717868 The information in this email is confidential and may be legally privileged. It is intended solely for the addressee. If you receive this email by mistake please notify the sender and delete it immediately. Opinions expressed are those of the individual and do not necessarily represent the opinion of Cambridgeshire County Council. All sent and received email from Cambridgeshire County Council is automatically scanned for the presence of computer viruses and security issues. _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l
