who mamages the epsg codes and transformations. I've never paid it much attention but I thought it had something to do with the proj4 packages.
On Fri, Jun 24, 2011 at 12:50 AM, Gerardo Jimenez <[email protected]> wrote: > Thanks for your answer but I found the problem and its solution. First my > data is in Nad 27, I am positivi about that. I found that QGis, depending on > the version, uses different epgs settings for UTM nad 27. Qgis 1.7 use an > argument to specify transformation parameters for WGS (+towgs84=). This is > the EPSG codein QGis 1.7 > > +proj=utm +zone=14 +ellps=clrk66 +towgs84=-10,158,187,0,0,0,0 +units=m > +no_defs > > Qgis 1.4,1.5 and 1.6 all stand alone versions on Windows do not define > these parameters. And that is the main reason of the problem. I found an > interesting link at > > http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryNorthAmericaTable.html > > that helped me to clarify that we can build a custom crs and add the > specific parameters for the area you are working. The ones of Qgis 1.7 are > the “Canadian Mean Solution” on this table. The parameters for my data on > utm zone 14N in Mexico are > > +proj=utm +zone=14 +ellps=clrk66 +towgs84=-12,130,190,0,0,0,0 +units=m > +no_defs > > With these parameters there are no differences in transformations made in > QGis, ArcMap and another program I use called Didger. > > For those interested in transformations dealing with local datums this link > is a good reference > > http://www.ecdisregs.com/get_pdf.php?id=62&action=view > > Thanks for your support! > > Gerardo Jiménez Delgado > Instituto de Investigaciones Antropológicas > Universidad Nacional Autónoma de México > Ciudad Universitaria s/n > Coyoacan 04510 Mexico City > Mexico 56 22 95 16 > >> Date: Thu, 23 Jun 2011 21:59:40 +1000 >> Subject: Re: [Qgis-user] Problem reprojecting a SHP >> From: [email protected] >> To: [email protected]; [email protected] >> >> one of the more spatially aware Northern hemisphere people may >> contradict me but.. if you look at.. >> http://en.wikipedia.org/wiki/File:Datum_Shift_Between_NAD27_and_NAD83.png >> the amount of shift your seeing looks suspiciously in the range of the >> difference between NAD27 and NAD83, are you positive your input data >> are in NAD27 and that your using the correct translations through the >> process? >> >> Your use of "UTM WGS 84" doesn't seem correct. UTM implies an XY >> coordinate system over a piece of the WGS84 spheroid and you need to >> specify a zone as well. >> >> good luck >> >> >> >> On Sun, Jun 5, 2011 at 4:32 AM, Gerardo Jimenez <[email protected]> >> wrote: >> > Hi >> > I have a dxf data whose coordinates are in UTM Nad27 zone 14q (14N for >> > any >> > GIS). I reproject the data to UTM WGS 84 either with vector tools or >> > save >> > as options and data I have from a GPS do not match my vector layer. I >> > posted >> > this also in the forum and followed the advise of building a KML from >> > my >> > original data. Same thing. I made an experiment, same dxf, exported to >> > shape, define UTM nad27 projection, and reproject to UTMwgs84 and build >> > a >> > kmz in ArcMap. QGis and ArcMap Nad 27 data do match perfectly. The wgs84 >> > data from QGIS and Arc Map differ about 80 meters (considerably if you >> > want >> > to use a vector layer displaying the streets of an entire city the size >> > of >> > Mexico City). The kmz from arcmap looks better in Google earth (streets >> > do >> > match better, not perfectly but better, the sat image) the the kml >> > produced >> > by QGis. So I wonder if anybody knows if I am doing something wrong or >> > if >> > the projection tools available in Qgis are working well. >> > For those interested I Include the experiment in the following file >> > >> > http://hotfile.com/dl/119748524/923a1a6/Prueba.zip.html >> > >> > Thanks before hand >> > >> > Gerardo Jiménez Delgado >> > Instituto de Investigaciones Antropológicas >> > Universidad Nacional Autónoma de México >> > Ciudad Universitaria s/n >> > Coyoacan 04510 Mexico City >> > Mexico 56 22 95 16 >> > >> > >> > _______________________________________________ >> > Qgis-user mailing list >> > [email protected] >> > http://lists.osgeo.org/mailman/listinfo/qgis-user >> > >> > > _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
