[Qgis-user] Geopagkage and "geom" in DBmanager

[DelazJ]

Hi,

I don't know how updated this is, but maybe
https://docs.qgis.org/testing/en/docs/user_manual/managing_data_source/create_layers.html#supported-query-language
from the docs could also shed some light.

Harrissou

Le jeu. 13 sept. 2018 à 12:43, Luigi Pirelli <luipir at gmail.com> a écrit :

> I dont' know in deep the detail of virtual layers, as far as I remember a
> virtual layer have a spatialite support of the virtualised layer. e.g. has
> all spatial operators. Geopackage, per definition ,if no spatialite
> extension has been loaded, is a simple container e.g. does not have any
> spatial operator => this should explain the mistery!
>
> Luigi Pirelli
>
>
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>
> On Thu, 13 Sep 2018 at 11:45, Bo Victor Thomsen <
> bo.victor.thomsen at gmail.com> wrote:
>
>> Hi Lene -
>>
>> I've made a few observations regarding the use of GeoPackage in
>> DBManager...
>>
>> I have a *GeoPackage* based table called "renhold" containing polygons.
>> Primary key column is an integer called "fid" and the geometry column is
>> called "geom" - It's pretty close to your setup
>>
>> If I use the *DBManager* with the *GeoPackage *dataprovider and execute
>> the following statement: *select fid, st_area (geom) from renhold , *it
>> returns a table with 2 columns as expected. However , column nr. 2 contains
>> only nulls. However, the statement does not result in an error. The
>> function "st_area" simply doesn't return a value besides null.
>>
>> An now the mystery!! :
>>
>> If I use the *DBManager* with the *Virtual Layers -> Project layers *dataprovider
>> and execute the following statement: *select fid, st_area (geometry)
>> from renhold , *it returns a table with 2 columns as expected. And
>> column nr. 2 do contain the expected area values. Go figure...
>>
>> NB! The "renhold" layer is visible in the map and named "renhold"
>> NBB! In the *Virtual Layers* dataprovider you have to use the standard
>> name "geometry" to represent the geometry column - not the real column name
>> ("geom" in this case)
>>
>> Actually I have a reasonable explanation: The 2 different dataproviders
>> uses different internal functions to calculate the area. However the
>> function used by the GeoPackage Dataprovider doesn't work !
>>
>>
>> Regards
>> Bo Victor Thomsen
>> LIFA Denamrk
>>
>> Den tor. 13. sep. 2018 kl. 09.27 skrev Alexandre Neto <
>> senhor.neto at gmail.com>:
>>
>>> Hi Lee,
>>>
>>> Can you try removing the quotation marks around geom?
>>>
>>> Best wishes,
>>>
>>> Alex Neto
>>>
>>> A qui, 13/09/2018, 02:04, Lene Fischer <lfi at ign.ku.dk> escreveu:
>>>
>>>> Hi,
>>>> Trying out a geopackage layer in DBManager asking a simple SQL
>>>> statement st_area
>>>> But when I try to write a statement like this
>>>>
>>>> SELECT "vandopland".* , st_area("vandopland"."geom") as areal_m2
>>>> FROM "vandopland"
>>>>
>>>>  "geom" is not found. Suggestions as geomfromexifgpsblob or geomfromfgf
>>>> or geomfromwkb . Then I get "an error occured"
>>>>
>>>> Any suggestions what I might have done wrong.
>>>>
>>>> Regards from a newbee Geopagkace/DBmanager
>>>>
>>>> Lene Fischer
>>>>
>>>>
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>>>
>>> --
>>> Alexandre Neto
>>> ---------------------
>>> @AlexNetoGeo
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>>
>>
>>
>> --
>> Med venlig hilsen
>>
>> Bo Victor Thomsen
>>
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