[gdal-dev] New behaviour of "PROMOTE_TO_MULTI" ?

Mon Aug 1 08:03:32 PDT 2022

Bo Victor,

there's an important mention in the email you quote: "The effect of this 
option is that when a layer is of type Polygon, it will be
converted in the target format as MultiPolygon,".    In your situation, 
the original layer geometry type is Geometry. There's no way that -nlt 
promote_to_multi can know that your geometries will actually be all 
polygon, or all linestring, and thus change the target layer geometry type.

We would probably a new option to ogr2ogr that would generalize the 
following open option of the shapefile driver:

ADJUST_GEOM_TYPE=NO/FIRST_SHAPE/ALL_SHAPES. Defines how layer geometry 
type is computed, in particular to distinguish shapefiles that have 
shapes with significant values in the M dimension from the ones where 
the M values are set to the nodata value. By default (FIRST_SHAPE), the 
driver will look at the first shape and if it has M values it will 
expose the layer as having a M dimension. By specifying ALL_SHAPES, the 
driver will iterate over features until a shape with a valid M value is 
found to decide the appropriate layer type.

You may file an enhancement ticket about that if you wish

Even

Le 31/07/2022 à 10:00, Bo Victor Thomsen a écrit :
>
> Thanks to Hugues and Richard for responding to my questions.
>
> However, I'm using the ogr2ogr inside a DOS .cmd file like this:
>
> for /R D:\tmp %%f in (*.tab) do ogr2ogr --config PG_USE_COPY yes 
> -progress -lco OVERWRITE=YES -lco SCHEMA=mat -dim XY -a_srs EPSG:25832 
> -f "PostgreSQL" PG:"host=localhost port=5432 user=*** password=*** 
> dbname=geodata" "%%f"
>
> I.e. iterating through a directory plus sub-directories and converting 
> every found tab file into a table into schema "mat" using ogr2ogr
>
> The tab files contains either points, linestrings or polygons. 
> Polygons and linestrings can be a mix of simple and multi-objects. 
> Each tab-file contains only one main type.
>
> So I can't use "-nlt multipolygons". And the point of this project was 
> to get rid of a fairly complex postgres based function that checks an 
> uploaded table and change its geometry type using "alter table ... 
> using st_multi(geom)" type of commands.
>
> That was why I tried to use "-nlt promote_to_multi". According to this 
> mail:
>
> https://lists.osgeo.org/pipermail/gdal-dev/2012-September/034128.html
>
> Even Rouault describes the exact behaviour I'm looking for: Simple 
> linestrings / polygons will be changed to multi types and points will 
> be left alone. And the geometry type will be set to a "multi*" as needed.
>
> What actually happens is that linestrings, polygons /and/ points all 
> are changed to multi type, but the geometry type remains "Geometry".
>
>
> Med venlig hilsen / Kind regards
>
> Bo Victor Thomsen
> Den 25-07-2022 kl. 15:52 skrev Hugues François:
>> Hi,
>>
>> I guess you should either
>> => drop the created table prior to launch the ogr2ogr command with 
>> the -nlt PROMOTE_TO_MULTI switch
>> => or maually alter the existing table: ALTER TABLE schema.table 
>> ALTER COLUMN geom TYPE geometry(MultiPolygon, SRID) using ST_MULTI(geom)
>>
>> HTH,
>> Hug
>>
>>
>> ------------------------------------------------------------------------
>> *De: *"Richard Greenwood" <richard.greenwood at gmail.com>
>> *À: *"Bo Victor Thomsen" <bo.victor.thomsen at gmail.com>
>> *Cc: *"gdal dev" <gdal-dev at lists.osgeo.org>
>> *Envoyé: *Lundi 25 Juillet 2022 15:32:35
>> *Objet: *Re: [gdal-dev] New behaviour of "PROMOTE_TO_MULTI" ?
>>
>> Have you tried -nlt MultiPolygon?
>>
>> On Mon, Jul 25, 2022 at 2:54 AM Bo Victor Thomsen 
>> <bo.victor.thomsen at gmail.com> wrote:
>>
>>     I have a MapInfo .tab file containing polygons, both simple and
>>     multipolygons (and only polygons).
>>
>>     Using this command: (all ogr2ogr commands are one-liners, but
>>     examples are split for lucidity)
>>
>>     ogr2ogr
>>       --config PG_USE_COPY yes
>>       -progress
>>       -lco OVERWRITE=YES
>>       -dim XY
>>       -f "PostgreSQL" PG:"host=localhost port=5432 user=***
>>     password=*** dbname=geodata"
>>       FREDSKOV.TAB
>>
>>     will (correctly) create a table in Postgres of PostGIS type
>>     "Geometry"
>>
>>     If I change the command to:
>>
>>     ogr2ogr
>>       --config PG_USE_COPY yes
>>       -progress
>>       -lco OVERWRITE=YES
>>       -dim XY
>>     *  -nlt PROMOTE_TO_MULTI*
>>       -f "PostgreSQL" PG:"host=localhost port=5432 user=***
>>     password=*** dbname=geodata"
>>       FREDSKOV.TAB
>>
>>     I would expect the table to change the PostGIS type to
>>     "MultiPolygon". However it still is registered as "Geometry".
>>
>>     Checking the table using SQL command:
>>
>>     SELECT ST_geometrytype(wkb_geometry), count(*) FROM mat.fredskov
>>     group by 1
>>
>>     affirms, that all geometries now is of type "ST_MultiPolygon".
>>
>>     AFAIK, this is a new behaviour. Or what ?
>>
>>     Postgres/Postgis version : 13.2,  3.1
>>
>>     OGR2OGR version:  both 3.4 andf 3.6 dev.
>>
>>
>>
>>
>>     -- 
>>     Med venlig hilsen / Kind regards
>>
>>     Bo Victor Thomsen
>>
>>     _______________________________________________
>>     gdal-dev mailing list
>>     gdal-dev at lists.osgeo.org
>>     https://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
>>
>>
>> -- 
>> Richard W. Greenwood
>> www.greenwoodmap.com <http://www.greenwoodmap.com>
>>
>>
>> [Fichier texte:ATT00001]
>
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