Turns out ArcMap's transformation on-the-fly does the same thing as cs2cs. What is postgis' transform doing differently?
Bryan > Hello, > > I'm not sure if this is the correct list for this question, but here goes. > If I ought to post to another list, please let me know which one. > > I'm seeing a discrepancy between coordinate transformations in postgis and > transformations using cs2cs with the exact same proj.4 string. Here are > the proj.4 strings and transformation using postgis: > > select proj4text from spatial_ref_sys where srid = 32003; > proj4text > ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ > +proj=lcc +lat_1=46.4 +lat_2=44.86666666666667 +lat_0=44 +lon_0=-109.5 > +x_0=609601.2192024384 +y_0=0 +ellps=clrk66 +datum=NAD27 > +to_meter=0.3048006096012192 +no_defs > (1 row) > > select proj4text from spatial_ref_sys where srid = 32100; > proj4text > -------------------------------------------------------------------------------------------------------------------------- > +proj=lcc +lat_1=49 +lat_2=45 +lat_0=44.25 +lon_0=-109.5 +x_0=600000 > +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs > (1 row) > > select astext(transform(setsrid(makepoint(1234488, 744181), 32003), > 32100)); > astext > ------------------------------------------ > POINT(366770.791392722 199138.151643548) > > Here is the transformation using cs2cs: > > cs2cs +proj=lcc +lat_1=46.4 +lat_2=44.86666666666667 +lat_0=44 > +lon_0=-109.5 +x_0=609601.2192024384 +y_0=0 +ellps=clrk66 +datum=NAD27 > +to_meter=0.3048006096012192 +no_defs +to +proj=lcc +lat_1=49 +lat_2=45 > +lat_0=44.25 +lon_0=-109.5 +x_0=600000 +y_0=0 +ellps=GRS80 +datum=NAD83 > +units=m +no_defs > 1234488 744181 > 366704.35 199132.53 0.00 > > Why the discrepancy? I'm guessing it has something to do with how datum > shifts are handled. So which one is right? That's probably going to > depend on something that I don't know about my input data, but maybe > someone will enlighten differently. Thank you. > > Bryan > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
