QGIS: alternative to add/edit virtual layer. With python?

Question

Following a previous question (Select polygons with other polygons layer?), I select some polygons using the query in the answer to create a virtual layer:

SELECT greens.*  FROM greens, purples
WHERE st_area(st_intersection(greens.geometry, purples.geometry)) 
      > 0.5 * st_area(greens.geometry)

It works really well, but my layers contain 1.800.000 (and sometimes more) polygons. So that QGIS freezes and virtual layers only appears few days later. When I am trying to record it, it takes again several days to do that. Since I have to do the operation on several layers, it takes an incredible amount of time (that I do not have). Does someone know an alternative to use that kind of query in an other way to select the right polygons?

What do you mean by "select the right polygons"? Is the query not producing correct results? — artwork21, Dec 18 '17 at 14:19
I meant selecting the polygons with more than 50% overlapping for example. But I think I have found the solution elsewhere: link — francois, Dec 18 '17 at 15:06

score 1 · Accepted Answer · answered Dec 18 '17 at 15:09

1

When I was thinking how to formulate the question, I thought a different way to look for in already-existing answers: I found a solution here: Programmatically finding polygons which are >90% overlapped by another vector polygon layer using QGIS?

answered Dec 18 '17 at 15:09

francois

195
7

QGIS: alternative to add/edit virtual layer. With python?

1 Answers1