[Gdal-dev] British National Grid to UTM

[Frank Warmerdam]

Roger Bedell wrote:
> Hi Frank,
> Well, it kind of works now, but here is the GDALINFO on the resulting TIF:
> 
> C:\openev_fw\bin>gdalwarp -s_srs EPSG:27700 -t_srs EPSG:32629 ss78.tif
> ss78utm.tif
...

> This is identical to the original SS78.TIF with the TFW. No warping seems to
> have been done.

Roger,

I believe the problem now is that gdalwarp doesn't know how to convert between
the OSGB 1936 datum and WGS84 so it just decides there is no reprojection
path and does essentially nothing. The lack of some sort of error report for
this is quite unfortunate, and something I will want to work on.

If you are willing to ignore datum shift effects you could apply the following
transformation:

gdalwarp -s_srs "+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.999601 +x_0=400000
                  +y_0=-100000 +ellps=airy +units=m +towgs84=0,0,0 +no_defs"
          -t_srs "EPSG:32629" ss78.tif ss78utm.tif

Or if you know an appropriate shift to convert to WGS84 you could supply
it in the +towgs84 option.

Best regards,
-- 
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