[Qgis-developer] Reading GEOJSON from string using GDAL

[Nyall Dawson]

On 19 February 2016 at 11:35, Even Rouault <even.rouault at spatialys.com> wrote:
> Le vendredi 19 février 2016 01:30:59, Nyall Dawson a écrit :
>> On 15 January 2016 at 06:57, Even Rouault <even.rouault at spatialys.com>
> wrote:
>> >> I've got a question regarding the geojson driver you may be able to
>> >> assist with. Is there any method in the OGR libraries which allow
>> >> direct parsing of a string to a  layer? (Ie, without first writing it
>> >> out to a file).
>> >>
>> >> I'd like to add the ability to directly paste geojson text into QGIS and
>> >> have it inserted as a feature in the current layer (like how you can
>> >> currently paste WKT text as a feature). I don't want to have to manually
>> >> parse the json (that would be a nightmare).
>> >
>> > Well, the GeoJSON driver support "filenames" which are in fact GeoJSON
>> > content:
>> >
>> > $ ogrinfo
>> > '{"type":"Feature","properties":{"foo":"bar"},"geometry":{"type":"Point"
>> > ,"coordinates":[2,49]}}' -ro -al
>> >
>> > Layer name: OGRGeoJSON
>> > Geometry: Point
>> > Feature Count: 1
>> > Extent: (2.000000, 49.000000) - (2.000000, 49.000000)
>> > Layer SRS WKT:
>> > GEOGCS["WGS 84",
>> >
>> >     DATUM["WGS_1984",
>> >
>> >         SPHEROID["WGS 84",6378137,298.257223563,
>> >
>> >             AUTHORITY["EPSG","7030"]],
>> >
>> >         AUTHORITY["EPSG","6326"]],
>> >
>> >     PRIMEM["Greenwich",0,
>> >
>> >         AUTHORITY["EPSG","8901"]],
>> >
>> >     UNIT["degree",0.0174532925199433,
>> >
>> >         AUTHORITY["EPSG","9122"]],
>> >
>> >     AUTHORITY["EPSG","4326"]]
>> >
>> > foo: String (0.0)
>> > OGRFeature(OGRGeoJSON):0
>> >
>> >   foo (String) = bar
>> >   POINT (2 49)
>> >
>> > Works also with FeatureCollections.
>> > Alternatively, you could also put the content in a in-memory GDAL file
>> > (/vsimem/ virtual file system) and open it.
>> >
>> > So you could likely instanciate a temporary layer and get a QGIS feature
>> > from that.
>>
>> Hi Even,
>>
>> I'm currently exploring this approach (in memory file), but I'm stuck
>> on how to actually write the string contents to a memory file prior to
>> opening to it with GDAL. I gather for the python bindings I could
>> utilise FileFromMemBuffer, but I can't find any similar replacement in
>> the c api.
>
> VSIFileFromMemBuffer :
> http://www.gdal.org/cpl__vsi_8h.html#a86b6b1c37bb19d954ee3c4a7e910120c
>
> And some code snippet here :
> http://www.gdal.org/cpl__vsi_8h.html#a66e2e6f093fd42f8a941b962d4c8a19e

Perfect - works great!!

Coming in QGIS 2.16... paste copied geojson text directly into a layer
as features :)

Nyall