QGIS – Creating Points Along Geometry in QGIS

qgis

I'm relatively new to QGIS, I have past experience with ArcGIS.

I am trying to place 9 equally spaced points along a line, including one at each vertex. The points represent posts along a trellis wire in an orchard.

I have tried both the answers in this post…
Creating specific amount of points along line in QGIS

First I used "Points along geometry"; changing the 'Distance' to $length/9
Next I used Geometry By Expression with the following code…

with_variable (
'no',
9,
collect_geometries (
array_foreach (
generate_series (0,@no-1,1),
line_interpolate_point(
$geometry,
length($geometry) / @no * @element
))))

My results are that 9 points are placed on each line, with a point on one vertex. However, I would like 9 points equally placed on each line with a point on both vertices.

QGIS version 3.22.10-Białowieża.
Windows 10.0.19044 Build 19044
Project Coordinate Reference System: EPSG: 2927 "NAD83 (HARN) /
Washington South (ftUS)
Project Units: Feet
Layer Coordinate Reference System: Same as the project.

Best Answer

Try this geometry by expression. It will place 9 points along the line length. For some reason I had to subtract 0.0001 or some lines didnt get the end point.

collect_geometries(
array_foreach(
generate_series(0, $length, $length/8-0.0001),
line_interpolate_point( $geometry, @element)))

Related Solutions

QGIS – How to Create Random Points Along Polyline

This code will work on the lastest dev build of QGIS.

from qgis.utils import iface
from qgis.core import *
from PyQt4.QtCore import QVariant
import random

def createRandomPoints(count):       
    # Create a new memory layer to store the points.
    vl = QgsVectorLayer("Point", "distance nodes", "memory") 
    pr = vl.dataProvider()  
    pr.addAttributes( [ QgsField("distance", QVariant.Int) ] )
    layer = iface.mapCanvas().currentLayer()

    # For each selected object
    for feature in layer.selectedFeatures():
        geom = feature.geometry()
        length = geom.length()
        feats = []
        # Loop until we reach the needed count of points.
        for i in xrange(0,count):
            # Get the random distance along the line.
            distance = random.uniform(0, length)
            # Work out the location of the point at that distance.
            point = geom.interpolate(distance)

            # Create the new feature.
            fet = QgsFeature()
            fet.setAttributeMap( { 0 : distance } )
            fet.setGeometry(point)
            feats.append(fet)

        pr.addFeatures(feats)
        vl.updateExtents()  

    QgsMapLayerRegistry.instance().addMapLayer(vl)

I know you said you are not very familiar with Python code but you should be able to run this pretty easy. Copy the above code into a file (mine is called locate.py) and place it in your ~/.qgis/python if you are on Windows 7 that will be in C:\Users\{your user name}\.qgis\python\ or on Windows XP C:\Documents and Settings\{your user name}\.qgis\python\

Once the file is in the python folder open QGIS and select some line objects.
Layer selection

Then open the Python console and run the following code:

import locate.py 
locate.createRandomPoints(10)

Python Console

The result should look something like this

Results

If you want to run it again just select some more lines and run locate.createRandomPoints(10) in the Python console again.

Note: locate.createRandomPoints(10) the 10 here is the number of points to generate per line

QGIS – Creating Points Along Geometry with Start and End Offsets

There are two problems in your approach:

$length calculates ellipsoidal distances. So you might want to use length($geometry) to get planimetric distances. Depending on what CRS you use and what distances you have, that might play a role or not.
Generate a series from 0 to 35 (36 points) and multiply this with the interval. Be aware: there are 35 intervals for 36 points. So the length of the interval is: line's length minus 3 (for 1.5 offset at start and end), divided by 35. Then add to this the start offset of 1.5 and multiply the @element for each point with the interval.

This is the expression to use:

collect_geometries( 
    array_foreach( 
        generate_series(0,35), 
        line_interpolate_point ($geometry,1.5+@element*(length($geometry)-3)/35)
    )
)

Demonstration for 26 points and offset of 15 from start-/endpoints:

Variant:

To easily change the no. of points and the offset, use variables.Change the values of 36 and 1.5 on lines 1 and 2 and the expression will automatically adapt:

with_variable('no_of_points',36,  -- change here
with_variable('offset',1.5,  -- change here
collect_geometries( 
    array_foreach( 
        generate_series (0,@no_of_points-1), 
        line_interpolate_point (
            $geometry,
            @offset + @element * (length ($geometry) - 2 * @offset) / (@no_of_points-1))
    )
)))

Best Answer

Related Solutions

QGIS – How to Create Random Points Along Polyline

QGIS – Creating Points Along Geometry with Start and End Offsets

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