[gdal-dev] Handling Ordnance Survey Change Only Updates

[Peter Halls]

Jez,

   I would be surprised if GDAL can handle OSGB MasterMap change-only 
updates automatically. The process defined by OS is to locate and replace 
the records concerned. Because the update may change the geometry of a 
record, I do not believe this can be done on a shapefile in situ. Instead 
the procedure would be to input the shapefile sequentially until a record 
to be changed is liocated, outputing the input to a new shapefile and 
substituting the change record for the input as appropriate, gaining a new 
shapefile. On completion, the new shapefile will have the correct spatial 
index and bounds. Indeed, it is probably most sensible to adopt this 
approach to such updates regardless of the output format, as this is 'safe' 
against update problems - which, in theory, could result from a problematic 
GML file and permits easy reversion.

Best wishes,

Peter
  
On Aug 16 2010, Jez Walters wrote:

>
>Hello fellow GDAL users!
>
>
>I need to handle Change Only Updates (COU) for the UK Ordnance Survey
>MasterMap Topography Layer, and I was wondering how to approach this.
>
>Both the initial and COU data are supplied as GML, and I am currently
>converting the initial data to ESRI shapefiles using ogr2ogr.  However, the
>ogr2ogr "-update" option won't update the shapefiles using the COU data -
>unless I'm missing something?
>
>I currently see two ways of overcoming this:
>
>1. Use the COU data to update the initial GML data, and then re-convert the
>merged data to ESRI shapefiles
>2. Use the COU data to directly update the ESRI shapefiles
>
>Obviously the second approach is more efficient, but how difficult is it to
>create, update and delete features using the GDAL python library?
>
>A few pointers for how to achieve this would be most welcome!  :-)
>
>
>Warm regards,
>
>
>Jez
>

-- 
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Peter Halls, University of York GIS Advisor
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