I've a very large linear shapefile wich represents pipes. I need to determine the position of every intersection between lines in this shape, only where no vertices already exists (I think with 0,-1 vertices) to create a new punctual layer. I've already tried some methods with lines intersection and validity checker with no luck.
In the following image I need to find the point indicated with the blue arrow, not the red circles. The red line (and the pink line intersected) is continuous.
Line Intersections to find points where different lines cross
Extract vertices to extract all existing vertices
Extract by expression Line intersection points that have no vertice nearby
array_length(array:= overlay_nearest(layer:= @Extract_vertices_OUTPUT , expression:=1, max_distance:=1))=0
Replace @Extract_vertices_OUTPUT with your vertice layer name.
This python script which you can run from the console with create points where 2 lines intersect and one or both does not have a vertex at the intersection points. It does not look for self-intersection.
# create point layer with points where either intersecting line or both do not have a vertex
from qgis.core import (
QgsProject, QgsGeometry, QgsFeature, QgsPointXY, QgsSpatialIndex
)
LAYER_NAME = "pipes"
pipes = QgsProject.instance().mapLayersByName(LAYER_NAME)[0]
epsg = pipes.crs().authid()
out = QgsVectorLayer(f"Point?crs={epsg}", f"{LAYER_NAME}_ints_one_or_none_vertices", "memory")
prov = out.dataProvider()
out.updateFields()
# Build vertex dictionary: { feature_id : set((x,y),...) }
vertex_dict = {}
for f in pipes.getFeatures():
verts = set()
for v in f.geometry().vertices():
verts.add((v.x(), v.y()))
vertex_dict[f.id()] = verts
index = QgsSpatialIndex(pipes.getFeatures())
added = 0
for f in pipes.getFeatures():
geomA = f.geometry()
bbox = geomA.boundingBox()
candidates = index.intersects(bbox)
for cid in candidates:
# skip self-intersections
if cid == f.id():
continue
# ensure pair only processed once
if cid < f.id():
continue
f2 = pipes.getFeature(cid)
geomB = f2.geometry()
inter = geomA.intersection(geomB)
if inter.isEmpty():
continue
pts = inter.asMultiPoint() if inter.isMultipart() else [inter.asPoint()]
for p in pts:
pt = (p.x(), p.y())
# Count how many of the two lines have a vertex at this point
has_vertex_A = pt in vertex_dict[f.id()]
has_vertex_B = pt in vertex_dict[cid]
count_vertices = has_vertex_A + has_vertex_B
# 0 -> no vertex on either line (add)
# 1 -> exactly one line has a vertex (add)
# 2 -> both lines have a vertex (skip)
if count_vertices == 2:
continue
# Add the point
feat = QgsFeature(out.fields())
feat.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(p)))
prov.addFeature(feat)
added += 1
QgsProject.instance().addMapLayer(out)
print(f"Done — added {added} intersection points (where 0 or 1 lines have vertices).")
