QGIS-Atlas get feature with multiple values

Question

I am looking for an expression to get_feature with two values from two different fields.

At its core is the question: How can I transform a chain of values which define a point into a valid geometry expression? For example for Point B:

?? geometry ("obj_art" = 'Ansicht' and "ptnr" = 'B') ??

Kasper has given us the answer to the question how a geometry can be defined over several values. You can use the aggregate ( ) expression. On the last position (filter:=), an arbitrarily long chain of values or conditions can be placed. The expression is unfortunately not self explanatory, but there are plenty of examples.

aggregate(layer:=' ', aggregate:=' ', expression:= , 
filter:="prof_nr"= @atlas_pagename and "obj_art"='Ansicht' and "ptnr" ='B' and so on and so on )

My Goal is to plot archaeological profiles via QGIS Atlas. Therefore I want to use Point A and Point B to filter page name. enter image description here As coverage layer I have a point layer in which point A and B are located. Both points have the same value in field "prof_nr" so that is page name. Both points are defined by two other values from two different fields (Image 1).

My approach is to make_line out of both points, so that I always get only one Atlas feature per archaeological profile on which the map zooms in the middle. Both points can be easily called by CASE WHEN but with the expression I do not succeed in creating a line (Image 1)

CASE WHEN "obj_art" = 'Ansicht' and "ptnr" = 'A' or "obj_art" ='Ansicht' and "ptnr" = 'B' THEN "prof_nr" END

Therefore I select only point A for page name and moved the make_line to the extents of the map (Image2, 3) enter image description here enter image description here

x_min( 
bounds( 
 make_line(
 start_point(@atlas_geometry),geometry(
 get_feature('E_Point', 'ptnr','B') 
 )
 )
 )
 )

Here I can connect both points with make_line, but with get_feature I can only assign a value from one field but to define the point I need two values from two fields for each point.

Does anyone have a solution?

• Babel: Sharing a project with sample data could help understanding the problem. Otherwise, one has first to try re-creating a similar project what quite takes some time that would be better spent on finding a solution.
• Al rl: Why not use the line generated from the point as your atlas layer? Or even group the points in a multipoint geometry?
• Janko: In my coverage layer there are other points to which the filter 'E_Point', 'ptnr','B' applies. Therefore I need to add another value from another field to specify the filter (and the point).
• Kasper: Have a look at the 'aggregate' function and it's examples, you will be able to get your feature thanks to an appropriate filter (ptnr = B and prof_nr = whatever needed)
• Janko: Tried a lot with something like: aggregate (layer:='E_Point',aggregate:='collect',expression:=bounds($geometry),filter:= "ptnr" ='B'and"obj_art"='Ansicht'). But its always a geometrie: emtpy, NULL or in this case a geometry: Multipolygon?

Answer 1

The Solution ist to override the x_Extents of the map!

For x_min I call point A

x_min(
aggregate (layer:='E_Point',aggregate:='collect',
expression:=bounds($geometry)
,filter:="prof_nr"= @atlas_pagename and "obj_art"='Ansicht' and "ptnr" ='A' )
 )

For x_max I call point B

x_max(
aggregate (layer:='E_Point',aggregate:='collect',
expression:=bounds($geometry)
,filter:="prof_nr"= @atlas_pagename and "obj_art"='Ansicht' and "ptnr" ='B' )
 )

Filter for pagename is to call Point A (or Point B, it doesn't matter)

CASE WHEN "obj_art" = 'Ansicht' and "ptnr" = 'A' THEN "prof_nr" END

That's it