[gdal-dev] Internal Metadata Management

[Frank Broniewski]

Hello Ari,

yes that is definitely helpful. But I still wonder if it might be 
easier/quicker to use GeoJSON as a interchange format and tranform from 
geojson to other formats than using OGRs internal structure. I already 
have some convenience classes for creating GeoJSON structures in Python. 
I know there is already a geojson python module [1], but onfortunately 
it doesn't deal with projections afaik.

Frank

[1] http://trac.gispython.org/lab/wiki/GeoJSON

Am 14.12.2010 09:40, schrieb 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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