qgis
I am trying to create midpoints for a set of polylines in QGIS. My python knowledge is poor and was wondering if there was a plugin that did if for me.
I have tried using the Mean Coordinates function suggested in Creating point to center of polyline? but this returns a centroid which is sometimes off the line (especially when lines are not straight). I am essentially looking for a point that is on the line half way along.
You can join the polylines by editing the layer, selecting all the lines (all of them or by attribute) and then click the 'Merge Features' tool:
To find the midpoint, calculate distance of lines, then use point along line tools to put a point at distance/2 along each line.
Well i want did the same but, i can´t find... this the way i solve it. Maybe can help to anybody
from qgis.core import *
import qgis.utils
canvas = qgis.utils.iface.mapCanvas();
layer = canvas.layer(1)
maxArea = 0
maxId = 0
selection =[]
uniquevalues = [];
dP= layer.dataProvider()
id = dP.fields().indexFromName('myColumn')
#i have the unique values from some column
uniquevalues = dP.uniqueValues( id )
#then i go for each value that is equal to my Unique value
for uv in uniquevalues:
exprec = QgsExpression( 'myColumn = ' + uv )
exprec.prepare( layer.pendingFields() )
for feature in layer.getFeatures():
value = exprec.evaluate( feature )
if bool( value ):
#areaDegs is the column what i want get the max value
if feature['areaDegs'] > maxArea :
maxArea = feature['areaDegs']
maxId = feature.id()
#here i store de Id´s width de Max values and unique values from myColumn
selection.append( maxId )
maxId =0
maxArea = 0
layer.setSelectedFeatures( selection )
Maybe there are a best way to do it, but for now, this is the way i do it.
Best Answer
There is a GDAL tool Points along lines (in
Processing Toolbox | GDAL | Vector geoprocessing).Start this tool, then set the
Distance from line start represented as fraction of line lengthparameter to0.5.This
0.5, being the fraction, puts a point at the middle of the line. For you most important part of this tool is that the points are placed on the line(s).