id summary reporter owner description type status priority milestone component version severity resolution keywords cc 3450 OSRExportToProj4() ignores towgs84 parameters if it recognises the datum name pkelly warmerdam "A GRASS user noticed a problem whereby in a certain co-ordinate reference system manipulation using the GRASS module g.proj, towgs84 parameters he was specifying were being discarded. I've tracked this down to OSRExportToProj4() where if it recognises a datum name from the WKT it does not attempt to look for a TOWGS84 clause. There may be a good reason for this, so I submit the attached patch (against SVN) with caution. As an example of how to reproduce the problem, consider the following WKT: PROJCS[""UTM Zone 6, Northern Hemisphere"", GEOGCS[""NAD27"", DATUM[""North_American_Datum_1927"", SPHEROID[""Clarke 1866"",6378206.4,294.978698213898, AUTHORITY[""EPSG"",""7008""]], TOWGS84[-5,135,172,0,0,0,0], AUTHORITY[""EPSG"",""6267""]], PRIMEM[""Greenwich"",0, AUTHORITY[""EPSG"",""8901""]], UNIT[""degree"",0.0174532925199433, AUTHORITY[""EPSG"",""9108""]], AUTHORITY[""EPSG"",""4267""]], PROJECTION[""Transverse_Mercator""], PARAMETER[""latitude_of_origin"",0], PARAMETER[""central_meridian"",-147], PARAMETER[""scale_factor"",0.9996], PARAMETER[""false_easting"",500000], PARAMETER[""false_northing"",0], UNIT[""Meter"",1]] As it is, this gets converted to: +proj=utm +zone=6 +ellps=clrk66 +datum=NAD27 +units=m +no_defs With the attached patch it gets converted to +proj=utm +zone=6 +ellps=clrk66 +datum=NAD27 +towgs84=-5,135,172,0,0,0,0 +units=m +no_defs This is more useful for our purposes anyway. I can't see any obvious side effects, but I fear I'm not aware of all the implications of this change so would not want to wholeheartedly recommend it - in particular I'm not sure how it might interact with the block of code else if( nEPSGGeogCS != -1 ) { [...] } and what that refers to. But I respectfully submit it for consideration anyway! (Relevant GRASS-user message: ) Thanks, Paul " defect closed high 1.8.0 OGR_SRS 1.7.2 normal fixed Markus Neteler sgamperl