[GIS] How to measure the distance of multiple points to a line

distanceqgisqgis-pluginsvector

I have two shapefiles in QGIS to which I am trying to find the distances between. I have a shoreline which is a vector line and then I have hundreds of data points in the ocean.

What I am trying to find is measuring the distance of each point to the corresponding place horizontally on the shoreline thus giving me a distance of each point from the shore. I have tried the distance matrix plugin which seems to only deal with point to point distances and have tried the mmqgis hub distance which only measures distances to a central fixed point on the line. Is there a plugin or way to find the distances I am looking for?

Best Answer

Try this: from the attribute table of your point file add a new field (real number) and use the following formula:

distance( $geometry , geometry ( get_feature( 'line-file','field',name-of-line))))

Were 'line-file' is the file where the line is stored, 'field' is a field in the line-file table, and name-of-line is the values of that field for your line. This formula gives only positive distance.

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If you can't get v.distance to work (it should be available through the GRASS plugin), you could try the NNJoin plugin that I uploaded to the QGIS plugin repository recently.

~~The NNJoin plugin does not use spatial indexes for line layers, so it is not practical if you have large datasets.~~

Edit: The current version of the NNJoin plugin can use spatial indexes also for polygon and line layers, so its performance has improved for large line and polygon datasets.

[GIS] NNJoin, MMQGIS and Nearest Neighbor QGIS failed to measure shortest distance

If you have to measure the distances once again, the following Python code may save you some time.

Have your points and lines loaded as map layers. Change the names 'point' and 'line' in line 4 and 5 resp. to the names of your layers. Copy the code into the Python console.

The function iterates over all points and finds the closest segment of all lines, and writes the closest position along the segment to a list. Then takes the position with the minimum distance to a points and builds a connecting line. The length of the line goes to the field distance.

d_lyr = QgsVectorLayer('LineString?field=distance:float', 'dist', 'memory')
QgsMapLayerRegistry.instance().addMapLayer(d_lyr)

p_lyr = QgsMapLayerRegistry.instance().mapLayersByName('point')[0]
l_lyr = QgsMapLayerRegistry.instance().mapLayersByName('line')[0]
d_lyr = QgsMapLayerRegistry.instance().mapLayersByName('dist')[0]
prov = d_lyr.dataProvider()
feats = []      
for p in p_lyr.getFeatures():
    minDistPoint = min([l.geometry().closestSegmentWithContext(QgsPoint(p.geometry().asPoint())) for l in l_lyr.getFeatures()])[1]
    feat = QgsFeature()
    feat.setGeometry(QgsGeometry.fromPolyline([QgsPoint(p.geometry().asPoint()), QgsPoint(minDistPoint[0], minDistPoint[1])]))
    feat.setAttributes([feat.geometry().length()])
    feats.append(feat)

prov.addFeatures(feats)
d_lyr.updateExtents()
d_lyr.triggerRepaint()

To test the code initiate 2 memory layers, a point layer named 'point' and a line layer named 'line', digitize some features, and run the code.

An example:

Best Answer

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