[gdal-dev] Internal Metadata Management

[Frank Broniewski]

Am 15.12.2010 16:47, schrieb Howard Butler:
>
> On Dec 15, 2010, at 9:30 AM, Ari Jolma wrote:
>
>> On 12/15/2010 05:11 PM, Frank Broniewski wrote:
>>>
>>> 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.
>>
>> GDAL has support for GeoJSON too. And it seems to support projections.
>
> GeoJSON explicitly supports projections, and OGR's implementation tries its best to deal with them.  GeoJSON's original intent is as a slightly-more-up-to-date, Javascript-consumable interchange format.  A better WKT, if you will.  With a light concept of features and feature collections.  It's a great way to interchange geometries and (sometimes) features between softwares of the Python world, the Javascript world, and the PostGIS world.
>
> There are some gotchas with GeoJSON as far as features are concerned though.  A GeoJSON feature object is essentially free-standing, and an array of them need not have a common schema to describe the layout of all of the features in that array.  In practice, the features of an array typically have a common schema, but this requirement is not enforced in any way.  This property of GeoJSON can cause some leakage in that respect.
>
> ESRI's JSON output is not GeoJSON, and AFAIK there is no interchange capability there.
>
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Hello Howard,

thank you very much for your detailed answer. I know that GeoJSON 
supports projections, the before mentioned python package (from Sean 
Gillies and Matt Russel) doesn't: "Version 1.0 does not consider 
coordinate systems." [1]

I am doing database based CAD to GIS conversions and therefore I was 
looking for an easy to use interchange format. Having used GeoJSON 
before with a number of OpenLayers Web applications, I know this format 
well and the really pleasant way to create this format from a number of 
different data sources. My only concern was actually if it wouldn't be 
more efficient to use OGRs internal data format directly. But I will be 
using GeoJSON as my transport format now. So I don't have to deal too 
much with OGRs C-API which I don't understand very well. I am just a 
geographer, not a programmer.

Luckily I won't have to deal with ESRIs data formats - apart from 
Shapefiles of course :-)


Frank

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