[gdal-dev] Extracting keys & values from OSM Planet

[Nikos Alexandris]

* Even Rouault <even.rouault at spatialys.com> [2017-11-20 15:59:51 +0100]:

>On lundi 20 novembre 2017 15:48:20 CET Nikos Alexandris wrote:
>> * Even Rouault <even.rouault at spatialys.com> [2017-11-07 22:37:02 +0100]:
>> >> 2. Is OGR handling well the conversion from .osm to ESRI Shapefiles?
>> >
>> >Yes, but within the limits ot the shapefile, and particularly .dbf format:
>> >limitation to 254 characters for field values, 10 characters for field
>> >names... which are easily violated by OSM extracts.
>> >
>> >Spatialite, GeoPackage, PostGIS etc. would be better choices as output
>> >format>
>> >> 3. What is the way to split "other_tags" in multiple new fields *when*
>> >> knowing exactly which tags are contained and should be obtained?
>> >
>> >Edit osmconf.ini to add in the attributes= settings the tag names you're
>> >interested in.
>> >
>> >Even
>>
>> Dear List,
>>
>> in a custom .ini file, under the [points] layer, an `attributes=`
>> instruction set of values that includes `natural,cave_entrance` (key and
>> value under OSM's Natural key), well extracts for the points layer some
>> existing nodes which bear the tag `natural:cave_entrance`.
>>
>> It is not required, as far as I understand the documentation, to include
>> both the parent key and any values (under it) of interest. Perhaps it may
>> be practical to have the attributes of interest split in a separate column.
>>
>> The command I tested, for example, is:
>>
>> ```
>> ogr2ogr --config OSM_CONFIG_FILE custom.ini -f SQLite -dsco SPATIALITE=YES
>> -gt 65536 -progress output.sqlite source.osm ```
>>
>> While this is sufficient for the work I am doing (I can filter
>> `cave_entrance`s out from the `natural` column in the `output.sqlite` file),
>> I wonder why the entries for some nodes correctly bear the string
>> `cave_entrance` in the `natural` column, yet the `cave_entrance` column
>> itself is empty for the same entries.
>
>The attributes keyword in osmconf.ini will select OSM tags whose *key* is one of the item
>specified in attributes.
>If you want to filter by value, you may add a -where or -sql clause  with something like
>"natural = 'cave_entrance'"

This works!

Yet, I can't seem to find an answer on the web, nor a solution by trying. I'd
like to perform SQL queries in one go: one querying the points layer and another
one the lines layer.

This is certainly not a JOIN operation, as far as I understand. And
UNION only works in data sourced from the same table/layer. Is it doable
to merge an 

SELECT *
FROM points
WHERE ...

and an

SELECT *
FROM lines
WHERE ...

query?

Thank you, Nikos
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