4

I have a line file and a polygon file in QGIS.

Primarily I am looking for any polygon that has a line intersecting it - easy, sorted.

From these intersects, I then want to pull out just the polygons that have a line going all the way through them and ignore those where the line ends within the polygon. See the below diagram for an explanation: I only want polygons 2 and 3.

Example

Does that make sense? I haven't managed to find any predefined tools thus far.

Taras
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JClarkson
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1 Answers1

6

There is a possibility using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer...

Let's assume we have two layers, namely 'lines_test' and 'polygons'

Input

With using this query it is possible to differentiate between line ending within polygon and line passing all the way through polygon.

SELECT *
FROM polygons
WHERE polygons.id NOT IN (
    SELECT polygons.id
    FROM polygons, lines_test
    WHERE ST_Within(ST_StartPoint(lines_test.geometry), polygons.geometry)
          OR ST_Within(ST_EndPoint(lines_test.geometry), polygons.geometry)
)

Output

References:

Taras
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