[gdal-dev] Guidance sought on using gdal-translate

[Christopher Hunt]

Hi Frank and friends,

Just to wrap this one up - we actually ended up receiving a geocoded  
image and I used gdal_translate to assign EPSG:27700 (the image was  
missing the coord sys declaration - this seems to be the case with a  
few image providers I've noticed):

gdal_translate -a_srs EPSG:27700 ...

Anyhow all good. Thanks for the help.

Cheers,
-C

On 16/08/2008, at 7:54 PM, Christopher Hunt wrote:

> Thanks for your reply Frank.
>
> On 16/08/2008, at 2:05 PM, Frank Warmerdam wrote:
>
>> I believe EPSG:27700 is British National Grid which is a projected
>> coordinate system based on the OSGB 1936 datum.  So you should
>> ensure the provider means the dataset is actually in BNG, in addition
>> to being based on OSGB 1936.
> OK, will do.
>
>> If you can get BNG coordinates then that is great.
> I've asked so fingers crossed.
>
>> If you can only
>> get WGS84 or OSGB1936 lat/long coordinates then you can
>> convert these to BNG using a program like cs2cs though that is
>> a bit tricky.
> Understood.
>
> Hopefully one last question on this though: the a_ullr parameters -  
> given the a_srs spec of EPSG:27700, are the a_ullr parameters  
> expected to be in BNG coordinates i.e. eastings and northings  
> values? Asking this another way, what actually dictates the  
> coordinate system used for the a_ullr parameters?
>
> Cheers,
> -C
>