> How do you convert old unprojected map files to AGD66? I may be wrong but I believe you cannot convert unprojected map files to any other datum. When you use File>Save Copy As... of a lat-long unprojected table (no datum) to a lat-long with a datum, it simply substitutes or associates the table to the new datum but does not change or convert any coordinates. Therefore this should only be done if you know the datum of the unprojected table. If the unprojected table in question is in fact Long-Lat AGD66 then there is no problem doing a save copy as ... and assigning that datum to the table.
Dan "David M Haycraft" <[EMAIL PROTECTED]> on 07/04/2002 07:24:38 PM To: "Mark Green" <[EMAIL PROTECTED]> cc: "MAPINFO-L" <[EMAIL PROTECTED]> Subject: Re: MI-L Re GDA94 or How can I offset all map objects 200m Mark The situation regarding Australian Bureau of Statistics (ABS) CDATA2001 and ABS CDATA96 is this. All ABS CDATA96 map files were created in the Long-Lat AGD66 coordinate system (aka Long-Lat AGD66 Projection). That's Australia Geographic Datum 1966. Use of the new Geographic Datum for Australia GDA94 (effectively the same as the WGS84 datum as used by GPS systems for example) has now been mandated for all Australian Government agencies. GDA94 does indeed shift everything about 200m NE compared to AGD66. ABS CDATA 2001 uses GDA94. MapInfo Pro can seamlessly mix-and-match true ADG66 and GDA94 map layers and the 200m discrepancies disappear by magic. For example I've just overlaid (AGD66) Tasmanian SLA boundaries from CDATA96 with (GDA94) Australian LandMass boundaries from MapInfo StreetWorks 6 and they fit perfectly. The technical term for mix-and-match is "re-project". Unfortunately MapInfo Pro allows -- and in fact encourages -- people to create earth map layers that have no explicit datum at all. These are often referred to"Unprojected Lon-Lat" tables. When you open one of these layers in Mapinfo Pro and click Map>Options>Projection, the Projection dialog shows Category="Long-Lat", Category member="Long-Lat" with no reference to any Datum. Obviously there's no way that MapInfo Pro can reproject one of these unprojected layers to register with a layer that has an explicit datum. Clearly this is an unfortunate state of affairs and an indictment on those who used to release MapInfo map files as "Unprojected Lon-Lat". Today most people know better. For example MapInfo Australia's new StreetWorks products are all in explicit GDA94 projection. For sure, the problems that you are having are due to the fact that your "legacy map files" are unprojected. The solution is simple in principle, namely convert your old unprojected map files to map files with an explicit AGD66 projection. As soon as you do this they will register with the new CDATA2001 files. Trust me :o) How do you convert old unprojected map files to AGD66? Simple: 1. open the old map file in a new MapInfo map window 2. confirm, by Map>Options>Projection, that it is indeed "unprojected" 3. use File>Save Copy As... and click the Projection button in the Save dialog window to choose Long-Lat AGD66, the save the copy with an different name from the original, or save it to a different folder. This process can take H O U R s if you have big map datasets. I have a free MapBasic program called DoFolder that lets you automate this procedure for a whole folder full of similar maps. Let me know if you're interested. Regards David M Haycraft Information Analysis Associates Pty Ltd ABN 47 085 516 105 1 Cumming Place, Wanniassa, 2903 Aust Capital Territory, Australia Phone/Fax: 61 + 2 + 6231 8104 Mobile: 0412 001 134 Email: [EMAIL PROTECTED] Web : www.acslink.aone.net.au/actaa/iaa.htm A MapInfo Technology Partner ----- Original Message ----- From: "Mark Green" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, 04 July 2002 18:37 Subject: MI-L Re GDA94 or How can I offset all map objects 200m > G'day mappers > > Just recieved my Cdata2001 from the ABS in Australia. > > All the Mapinfo files are now in GDA94 projection. > > If I overlay the new files over the old ones they are out by around > 205metres to the North East. > > I need to convert my old files and a lot of legacy files to match the new > ones. > > In effect I need to move all the objects in a file 205 metres in a certain > direction. > > Most of my files are over 50 mb so sitting there selecting them and moving > is not an option. > > Does anyone know of a tool or some MB code that will allow me to automate > the process. > > Thanx In Advance. > > Mapping Man > Mark Green > > > --------------------------------------------------------------------- > List hosting provided by Directions Magazine | www.directionsmag.com | > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
