It is true that "datum 0" means "no datum". However, datum 0 will behave as a sphere _only_ if it is used by itself. When used with another table in a map window, the map will project using the datum of the other table, even when the other table is projected. If you use Map->Options to explicitly select "Latitude/Longitude" without a datum, the map will stubbornly stick to the other datum! Try this using World (which uses the Robinson projection) and your datum 0 table.
Because of this, if you use File->Save Copy As and save the table as latitude/longitude using a named datum, MapInfo (6.5 and 8.5) will not change the table's coordinates. I was able to change the intrinsic datum of a table (lat/lon in datum 33) by using "File->Save As" twice (first to datum 0, then to the other datum), and verified it by exporting the two files to MIF and running a file compare in TextPad. The only difference between the two MIF files was the datum number in the Coordsys clause. (saving to datum 0 really did change it to datum 0). HTH Spencer -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tim Rideout Sent: Tuesday, August 01, 2006 3:51 AM To: [email protected] Subject: [MI-L] CoordSys Earth Projection 1, 0 I think it means there is no datum. In other words you are using spherical co-ordinates on what is assumed to be a perfect sphere. The latitude - longitude reference system obviously works on any spherical object with an axis of rotation, whether it is the earth, mars, or a football. You should find out what is the correct datum for your data and then replace the 0 in the co-ord sys statement with the correct number. Don't reproject your data because that will move the positions, and that almost certainly isn't what you want to do. Tim Dr Tim Rideout Director Visit XYZ at the Frankfurt Book Fair, Oct 4 - 8th 2006, Intergeo Munich Oct 10-13th 2006 or IMTA World in Singapore, Nov 2006. The XYZ Digital Map Company Unit 9 Phase 2 Hardengreen Business Park Dalhousie Road, Dalkeith EH22 3NX, Scotland, Europe Tel: +44 131 454 0426 Fax: +44 131 454 0443 Mobile: +44 7766 825937 Email: [EMAIL PROTECTED] Web: www.xyzmaps.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: 01 August 2006 00:11 To: [email protected] Subject: [MI-L] CoordSys Earth Projection 1, 0 I have a number of tables with the following coordsys statement in the MIF file CoordSys Earth Projection 1, 0 In the map window, it comes up as lat/long projection, but no datum is mentioned. What datum is 0? I can't find it listed in the manual. Regards, Nick Lawrence ************************************************************ Opinions contained in this e-mail do not necessarily reflect the opinions of the Queensland Department of Main Roads, Queensland Transport or Maritime Safety Queensland, or endorsed organisations utilising the same infrastructure. If you have received this electronic mail message in error, please immediately notify the sender and delete the message from your computer. ************************************************************ _______________________________________________ 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 _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l
