On Wed, Mar 31, 2010 at 6:52 PM, Frank Warmerdam <[email protected]> wrote: > Markus Neteler wrote: >> >> Hi, >> >> (back to an old problem) >> >> On Fri, Jul 24, 2009 at 4:31 PM, Markus Neteler <[email protected]> wrote: >>> >>> Hi, >>> >>> I am trying to reproject Slovenian country data from D48 (WKT attached) >>> and Italian ISTAT national vector data (UTM32/ED50) into a common >>> projection. >>> >>> While the map "attach" rather well in Latlong/WGS84 using GDAL 1.6.svn, >>> they don't in EU LAEA (EPSG 3035). This is a bit suprising for me. >>> Any trick to get this done? >>> >>> The input SHAPE files have each a .prj file (attached), the target SRS >>> I request by -t_srs epsg:4326 or -t_srs epsg:3035. >>> >>> My preferred SRS would be EU LAEA to match the EU CORINE data. >> >> It appears to be a bug in GDAL. >> If I do >> >> * SLO -> EU LAEA >> the result is shifted, apparently the TOWGS84 in epsgD48_3787.prj is >> not applied. >> >> If I do instead: >> * SLO -> LL -> EU LAEA >> the result is "perfect". > > Markus, > > The problem is that the eu_etrs89_laea.prj does not have TOWGS84 > parameters for the datum, so if you go directly from D48 to laea > no datum shifting will be done (since one end is not datum enabled).
Ah - I didn't realize this. > If you go to WGS84 first, then the D48 datum shift is applied to WGS84. > No datum shift is applied from WGS84 to the LAEA projection, but ETRS89 > is effectively the same as WGS84 I believe. Yes, I think so. > So the key is to mark the ETRS89 datum as equal to WGS84 - likely with a > TOWGS84[0,0,0] entry in the coordinate system definition. OK, I'll prepare accordingly my ETRS89 .prj template to avoid this problem in future with my current GDAL 1.7.svn installation. [ I wonder if gdal* could say that the datum shift was omitted to wake up the user...] > I see that after my datum overhaul, GDAL is expanding EPSG:4258 to: > > GEOGCS["ETRS89", > DATUM["European_Terrestrial_Reference_System_1989", > SPHEROID["GRS 1980",6378137,298.257222101, > AUTHORITY["EPSG","7019"]], > TOWGS84[0,0,0,0,0,0,0], > AUTHORITY["EPSG","6258"]], > PRIMEM["Greenwich",0, > AUTHORITY["EPSG","8901"]], > UNIT["degree",0.01745329251994328, > AUTHORITY["EPSG","9122"]], > AUTHORITY["EPSG","4258"]] > > which has the TOWGS84[] entry, so we can have confidence that this > family of problem will be reduced as the richer set of datum shifts > comes out with GDAL 1.8. > > In short, I think this is an understood situation and there is no > need for a ticket. Perfect. Thanks for the explanations, Markus _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
