[gdal-dev] 3D extent

[Even Rouault]

(re-adding the list)

Le 23/06/2023 à 11:34, B. De Mezzo a écrit :
>
> Thanks!
>
> I will try this sql request to handle this specific case.
>
> Do you think it could be possible to have a OGR_L_GetExtent3D() 
> function which returns, as a default implementation, the 
> OGR_L_GetExtent() result and with 0.0 (or NaN) for the Z coordinates? 
> Future works can re-implement the OGR_L_GetExtent3D driver function to 
> fit the real data.
>
That's technically possible, but at bit odd. I'd say that while at it, 
it would be much better to have a default generic implementation in the 
base OGRLayer class that does the iteration, just like the 2D version at 
https://github.com/OSGeo/gdal/blob/master/ogr/ogrsf_frmts/generic/ogrlayer.cpp#L230 
. Driver specializations could indeed come afterwards
>
> Benoit.
>
> Le 23/06/2023 à 11:25, Even Rouault a écrit :
>>
>> Benoit,
>>
>> Indeed OGR_L_GetExtent() will never fill the Z fields, since it has 
>> no idea they are there. So a 3D specific function would be needed.
>>
>> But in the case of GeoPackage, as many/most other formats, layer 
>> extent metadata doesn't include the Z component either. The generic 
>> option is to iterate over all features and use OGR_G_GetEnvelope3D() 
>> on their geometry.
>>
>> In the specific case of GeoPackage, you could also issue a 
>> ExecuteSQL("SELECT MIN(ST_MinZ(geometry_column_name)), 
>> MAX(ST_MaxZ(geometry_column_name)) FROM layer_name") which should be 
>> faster on big layers
>>
>> Even
>>
>> Le 23/06/2023 à 11:14, B. De Mezzo a écrit :
>>>
>>> Hi,
>>>
>>> I was looking for a solution to retrieve a 3D extent (in my case 
>>> from a gpkg). Currently, the OGR_L_GetExtent function uses an 
>>> OGREnvelope and when I pass a OGREnvelope3D parameter, it does not 
>>> fill the Z fields.
>>>
>>> What should be the best approach to the minZ and maxZ for a layer?
>>>
>>> Regards.
>>>
>>>
>>> _______________________________________________
>>> gdal-dev mailing list
>>> gdal-dev at lists.osgeo.org
>>> https://lists.osgeo.org/mailman/listinfo/gdal-dev
>> -- 
>> http://www.spatialys.com
>> My software is free, but my time generally not.

-- 
http://www.spatialys.com
My software is free, but my time generally not.
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