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I have some data in a PostGIS table with the projection EPSG 27700. If I export this data from QGIS (v1.8) to MapInfo TAB / MIF when I open the data in MapInfo it has a shift on it.

Does anyone know why this happens? I don't get any problems if I open MapInfo data directly into QGIS, but I did notice that QGIS opens the data with a custom projection.

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QGIS 1.8 is not a stable release (beta) - then it would be a bug with GDAL correct? –  Mapperz Sep 6 '11 at 13:47
    
I guess I will test using an older version of QGIS / GDAL to see if it makes a difference. –  James S Sep 7 '11 at 9:42

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I'm unable to comment at the moment, so my only option is to reply here, although this isn't an answer.

Can you describe what the magnitude of the shift is and how you are observing it - comparing the reported coordinates of vertices in QGIS and MapInfo, or comparing the alignment with a different dataset? If the latter, then is the other dataset also British National Grid, or might there be a coordinate system transform being done on the fly by both MapInfo and QGIS, as this would probably generate different shifts in the data.

Further exploration: If you view the coordinates for one feature directly from PostGIS by converting the geometry to WKT, how do the numbers compare to those observed in the MIF file - is the shift observed between these stages?

Following on from your comments, this is now an answer!

The shift that you describe corresponds exactly to what would be seen if the MIF file defined British National Grid using the WGS84 datum rather than the (correct) OSGB36 datum. On import, MapInfo will reproject the coordinates to their BNG position, which generates the shift.

You should be able to confirm this by examining the Coordsys line of the MIF file, which will begin CoordSys Earth Projection 8, 104 (BNG using WGS84). If you alter this portion of the line to CoordSys Earth Projection 8, 79 (BNG using OSGB36) the coordinates should appear in the correct location.

I can recreate this behaviour in QGIS 1.7 (which uses GDAL 1.8) - this is a bug, but most probably in GDAL rather than QGIS itself (more investigation required!). A workaround is to export to ESRI Shape (or GML) and then open that in MapInfo, specifying British National Grid as the Coordinate System.

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Well the shift appears to be as follows: QGIS - point at 398324.07, 88287.55. I exported a GML and a MIF file from QGIS and they both say the coordinates should be 398324.07, 88287.55. Imported into MapInfo from MID/MIF - if I double click on the point it gives the coordinates 398419.89, 88208.22. –  James S Sep 7 '11 at 14:08
    
When importing the MID/MIF MapInfo doesn't recognise the projection as British National Grid even though QGIS has the projection set as 27700. –  James S Sep 7 '11 at 14:27
    
Thank you so much for this answer. absolutely spot on with what was happening. MapInfo wont open a shapefile or import a gml file of the data so I just amended the 104 to 79 in the mif file. It seems to have done the trick. Been causing me a lot of annoyance. –  James S Sep 8 '11 at 10:25
    
Are you using a very old version of MapInfo? I think Shapefile opening was introduced in v7.8. Not sure when GML import came in though. –  Andy Harfoot Sep 8 '11 at 10:34
    
I am using v11. Just doesn't seem to like the file. Opens and imports other files. –  James S Sep 8 '11 at 10:43

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