[gdal-dev] Internal Metadata Management

[Ari Jolma]

Frank,

A FeatureDefn is typically shared by all features in a layer and you 
need one to create a feature object. Feature class has SetField and 
GetField methods for storing and retrieving the attributes of a feature.

I hope this helps,

Ari

On 12/14/2010 09:33 AM, Frank Broniewski wrote:
> Hello,
>
> I have a question concerning OGR's metadata or attribute management 
> when converting between geodata vector formats. My question is maybe 
> only loosely related to OGR and aims at the internal management of 
> attribute data.
>
> From what I have read and understood from the documentation, OGR uses 
> the OGC Simple Feature Specifiaction to transform data from one format 
> to another. While reading the OGC specs I could not find a notion on 
> how one should deal with attribute metadata, the whole spec seems to 
> be about vector geometries only.
>
> Why I ask this: I am a Python user using the ogr python bindings and 
> now the need arose that I need to write a flexible geo format exchange 
> software. I chose OGR as a base for doing the conversion. My data 
> often comes from databases with non standard data and geoemtry 
> formats. So I want to align with OGR's internal used Simple Feature 
> Data format, but I don't know how/where I should put the attributes / 
> metadata. I see that the Feature is the part I have to look at because 
> it has the geometry and the FeatureDfn. Unfortunately this is the part 
> I don't understand :-)
> I need to create a FeatureDfn for my Feature which is basically the 
> column names and data types? Where do I put my attribute values then? 
> I looked at the OGRFeatureDefn Class Reference, but my understanding 
> of OGR is too low to understand how this relates to the OGRFeature.
>
> So basically I am looking for a starter tip that pushes me into the 
> right direction. Is there some python tutorial somewhere which I 
> missed or somebody has a code snippet for me?
>
> Or would it be easier to use internally a format like geojson and use 
> this as a starter for converting to other formats? Can OGR always 
> transfer the attributes of my geospatial data to other formats?
>
> I am sorry that my question is somewhat unclear, but I have some 
> difficulties to find the right form for my question. But I hope that I 
> could state my problem in an understandable way :-)
>
> Many thanks for any tipps
>
> Frank
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