[Qgis-user] Atlas: Filter Empty Pages

[Albin Blaschka]

Hello!

So, finally, I was successful: The idea with the virtual layer made it 
simple, as the point data is a postgis layer anyway, after storing the 
grid in the database, I created a view, where I have my grid and the 
count of points per cell, which I use for the creation of the atlas. 
Brings other advantages as well... (...wondering why I had this idea not 
earlier...)
The only caveat was that QGIS did not want to load the view as layer 
directly - It said, the layer is not valid. But after doing a "select * 
from myview" in the DB-Manager and adding the result as layer, it 
worked. Will look into it later...
(Postgres 9.4.6, PostGIS 2.1, pretty standard Ubuntu server - QGIS 2.14 
on Win7 - maybe somebody has an idea on that, too?)

Thank you all for your help and specially Andreas!
best regards,
Albin

Am 21.03.2016 um 17:00 schrieb Andreas Neumann:
> hm - actually, I was wrong.
>
> It is not so easy to filter dynamically - as $geometry equals 
> @atlas_geometry and you don't have a relation with the points.
>
> My next try would be to use a "Virtual Layer" and add a spatial 
> relationship between your atlas coverage layer (the grid) and a column 
> containing the count of points within the atlas feature.
>
> See 
> https://www.qgis.org/en/site/forusers/visualchangelog214/index.html#feature-virtual-layers
>
> You need QGIS 2.14 to use the virtual layers.
>
> You can add a virtual column to the atlas coverage layer that uses a 
> spatial relation, group by and count. If the count is zero you can 
> filter that coverage feature away.
>
> This should hopefully work. Let us know if you are stuck.
>
> Andreas
>
> On 21.03.2016 16:41, Andreas Neumann wrote:
>> Hi Albin,
>>
>> You can do this dynamically. The Atlas filter also accepts geometry 
>> relationship functions. Have a look at the QGIS expression editor.
>>
>> You can try with the intersects / within / overlaps tests and test 
>> $geometry against @atlas_geometry.
>>
>> Your filter could look like:
>>
>> within( $geometry,  @atlas_geometry )
>>
>> Can you please report back if that works?
>>
>> Greetings,
>> Andreas
>>
>>
>>
>> On 21.03.2016 14:47, Albin Blaschka wrote:
>>> Am 21.03.2016 um 14:20 schrieb Bernd Vogelgesang:
>>>> sounds maybe to easy, but why don't you just make a spatial query 
>>>> on your coverage grid to select and save those elements which do 
>>>> have points inside (Grid Layer Contains Points Layer e.g.) and then 
>>>> use that new coverage layer to produce your Atlas?
>>>>
>>>> Or do you search for a more clever approach?
>>>>
>>>> Cheers
>>>> Bernd
>>>
>>> Hello Bernd, Joris & List!
>>>
>>> Ah, yes - that would be a possibility, which I did not think of - 
>>> Thank you both!
>>> ...but in general I was on the quest for a "more clever" meaning 
>>> here "dynamic" approach, I have to admit: So, the aim would be in 
>>> future, just opening the project, printing the atlas without further 
>>> intervention and getting an "up-to-date" atlas...
>>> But in the meanwhile, it should be ok with the "manual" approach.
>>>
>>> Thanks and greetings!
>>> Albin
>>>
>>>> Am 21.03.2016, 13:53 Uhr, schrieb Albin Blaschka 
>>>> <albin.blaschka at standortsanalyse.net>:
>>>> Hello List!
>>>>
>>>> I am starting to use the Atlas feature for the first time and had 
>>>> the following problem:
>>>> I have a coverage-layer (a vector grid) and a point layer 
>>>> (collection sites). At the moment, there are grid cells in which no 
>>>> site (point) is located.
>>>> My problem is: I would like to filter those "empty" 
>>>> atlas-elements/pages out. In other words, if the atlas-page 
>>>> contains no element of the point layer, it should not get 
>>>> printed/produced.
>>>> I tried myself and failed, I googled and failed...
>>>>
>>>> Is this possible and if yes, how?
>>>>
>>>> Thanks in advance,
>>>> Albin
>>>
>>
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