Identifying the two points ending a line in QGIS

proximityqgisqgis-3

Project : footpath going from point to point
I have two layers
Layer 1 points, each point is corresponding to a stake showing a unique number (the unique id of this layer
Layer 2 lines, the route going between each point. Between each point is a single line.

I want to create a field in layer 2 that will be populated with the unique number of the 2 points (start and end)
Example:
layer points : 3 points 1,2,3
layer line, 3 lines : point 1 to 2, 2 to 3, 3 to 1
the field should be respectively populated with 1-2, 2-3, 3-1

The points are exactly at the start/end of lines, snapping was used to create them

How can I do this using
QGIS version 3.16.16? I have no idea how to make this.

Best Answer

You can use Field Calculator.

function aggregate Returns an aggregate value calculated using features from another layer.

aggregate(layer:='checkpoint', aggregate:='concatenate', expression:="checkpointid", filter:=intersects($geometry, geometry(@parent)), concatenator:=',')

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[GIS] Creating points along line according to attribute data using QGIS

Here's a quick PyQGIS script which should do the trick

from qgis.core import QgsFeature, QgsVectorFileWriter, QgsGeometry

def create_points(feat,writer):
    geometry = feat.constGeometry()
    if not geometry:
        return
    length = geometry.length()
    # -----------------
    # change 'num_points' to match your field name for the number of points field
    # -----------------
    num_points = feat['num_points']
    delta = length / ( num_points + 1.0 )
    distance = 0.0
    for i in range(num_points):
        distance += delta
        output_feature = QgsFeature(feat)
        output_feature.setGeometry( geometry.interpolate(distance) )
        writer.addFeature(output_feature)

layer = iface.activeLayer()

# ---------------
# change 'd:/test_points.shp' to desired output file name
# ---------------

writer = QgsVectorFileWriter('d:/test_points.shp',None, layer.fields(), QGis.WKBPoint, layer.crs())

for f in layer.getFeatures():
    create_points(f,writer)

del writer

Just change the num_points field name and output file name to match your data, select the input layer, and run it in the python console.

[GIS] Creating a line from two points in QGIS

You might like the following process. Be aware it doesn't create a physical line layer in a different shapefile but a visual line layer from your data only visible within your QGIS project.

Load in your table data (via the Spreadsheet Layers plugin for example), and make the point geometry from the X and Y start column.
For the moment you will have your starting point data on screen.
Right click on the point layer and go to properties
Open the Style tab
Choose Single symbol, then geometry generator

Geometry generator

Choose LineString type in the list
Enter the following command, X_Start, Y_Start, X_End, Y_End being your 4 start and end fields :

make_line( make_point( "X_Start","Y_Start"),make_point( "X_End","Y_End"))

Line generator

Instead of seeing point, you will see lines going from the starting point to the end point.

Best Answer

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[GIS] Creating points along line according to attribute data using QGIS

[GIS] Creating a line from two points in QGIS

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