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

[Bo Victor Thomsen]

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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