The Brazilian 6� Transverse Mercator has eight zones starting at zone 1 with a Central Meridian of 30�W and continuing to 72�W. Although the Central Meridian's False Easting is 500 Km, the Scale Factor at Origin is NOT 0.9996 but rather is 0.99933333333...3. The False Northing is 5,000 Km at the Equator rather than UTM's value which is double of that. The most common classical datum is Corrego Alegre 1949 and it is referenced to the International ellipsoid of 1909. There are many other local astro points used as datums throughout the 20th century in Brazil, mostly along the coast or way into the "boonies." All new surveys in Brazil are on SIRGAS (the South American version of WGS84/ITRF_XX). Clifford J. Mugnier Chief of Geodesy and Associate Director, CENTER FOR GEOINFORMATICS Department of Civil Engineering CEBA 3223A LOUISIANA STATE UNIVERSITY Baton Rouge, LA 70803 Voice and Facsimile: (225) 578-8536 [Academic] Voice and Facsimile: (225) 578-4474 [Research] ====================================================== http://www.asprs.org/resources/GRIDS/ http://www.cee.lsu.edu/facultyStaff/mugnier/index.html ====================================================== Any Brazilian or international coordinate system experts in the house? I have a shapefile of Brazilian data which came without a PRJ file to give away essential information about the coordinates used. The numbers are large so I guessed they were metres on a UTM projection. Since the data covers all of Brazil (which crosses multiple UTM zones), I guessed on a mid-strip of 22S which turned out to be "almost right". Viewing on ArcView or MapInfo Pro, I see a (slightly varying) ~100km shift west for the data when overlaid on reference data. The vertical seems about right. This error is much more than I would expect for a datum issue but I tried all the common ones anyway - no real difference. Does anyone know if Brazil uses some system which differs from the standard zones such as a different false easting? Regards, Warren Vick Europa Technologies Ltd. http://www.europa-tech.com --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 16235 --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 16240
