Looking to do a basic Hex analyis with some random points within the Gulf of Mexico.
I created a hex grid from MMQGIS
Under my Vector tool – Analysis tools, I dont have Points in Polygon.
Is it missing on 2.16.3 (2.16.x)?
[GIS] Points in Polygon missing from QGIS 2.16.x
hexagon-binninghexagonal gridqgis-2.16qgis-plugins
Related Solutions
My solution involves a PyQGIS script that is faster and more effective than a workflow involving snapping (I gave it a try too). Using my algorithm I've obtained these results:
You can run the following code snippets in sequence from within QGIS (in the QGIS Python console). At the end you get a memory layer with the snapped routes loaded into QGIS.
The only prerequisite is to create a multipart road Shapefile (use Processing->Singleparts to multipart, I used the field fictitiuos as Unique ID field parameter). This will give us a roads_multipart.shp file with a single feature.
Here is the algorithm explained:
Get the nearest hexagon sides where routes cross. For each hexagon we create 6 triangles between each pair of neighbour vertices and the corresponding centroid. If any road intersects a triangle, the segment shared by the hexagon and the triangle is added to the final snapped route. This is the heavier part of the whole algorithm, it takes 35 seconds running on my machine. In the first two lines there are 2 Shapefile paths, you should adjust them to fit your own file paths.
hexgrid = QgsVectorLayer("/docs/borrar/hex_grid_question/layers/normal-hexgrid.shp", "hexgrid", "ogr") roads = QgsVectorLayer("/docs/borrar/hex_grid_question/layers/roads_multipart.shp", "roads", "ogr") # Must be multipart! roadFeat = roads.getFeatures().next() # We just have 1 geometry road = roadFeat.geometry() indicesHexSides = ((0,1), (1,2), (2,3), (3,4), (4,5), (5,0)) epsilon = 0.01 # Function to compare whether 2 segments are equal (even if inverted) def isSegmentAlreadySaved(v1, v2): for segment in listSegments: p1 = QgsPoint(segment[0][0], segment[0][1]) p2 = QgsPoint(segment[1][0], segment[1][1]) if v1.compare(p1, epsilon) and v2.compare(p2, epsilon) \ or v1.compare(p2, epsilon) and v2.compare(p1, epsilon): return True return False # Let's find the nearest sides of hexagons where routes cross listSegments = [] for hexFeat in hexgrid.getFeatures(): hex = hexFeat.geometry() if hex.intersects( road ): for side in indicesHexSides: triangle = QgsGeometry.fromPolyline([hex.centroid().asPoint(), hex.vertexAt(side[0]), hex.vertexAt(side[1])]) if triangle.intersects( road ): # Only append new lines, we don't want duplicates!!! if not isSegmentAlreadySaved(hex.vertexAt(side[0]), hex.vertexAt(side[1])): listSegments.append( [[hex.vertexAt(side[0]).x(), hex.vertexAt(side[0]).y()], [hex.vertexAt(side[1]).x(),hex.vertexAt(side[1]).y()]] )Get rid of disconnected (or 'open') segments by using Python lists, tuples, and dictionaries. At this point, there are some disconnected segments left, i.e., segments that have one vertex disconnected but the other one connected to at least other 2 segments (see red segments in the next figure). We need to get rid of them.
# Let's remove disconnected/open segments lstVertices = [tuple(point) for segment in listSegments for point in segment] dictConnectionsPerVertex = dict((tuple(x),lstVertices.count(x)-1) for x in set(lstVertices)) # A vertex is not connected and the other one is connected to 2 segments def segmentIsOpen(segment): return dictConnectionsPerVertex[tuple(segment[0])] == 0 and dictConnectionsPerVertex[tuple(segment[1])] >= 2 \ or dictConnectionsPerVertex[tuple(segment[1])] == 0 and dictConnectionsPerVertex[tuple(segment[0])] >= 2 # Remove open segments segmentsToDelete = [segment for segment in listSegments if segmentIsOpen(segment)] for toBeDeleted in segmentsToDelete: listSegments.remove( toBeDeleted )Now we can create a vector layer from the list of coordinates and load it to the QGIS map:
# Create a memory layer and load it to QGIS map canvas vl = QgsVectorLayer("LineString", "Snapped Routes", "memory") pr = vl.dataProvider() features = [] for segment in listSegments: fet = QgsFeature() fet.setGeometry( QgsGeometry.fromPolyline( [QgsPoint(segment[0][0], segment[0][1]), QgsPoint(segment[1][0], segment[1][1])] ) ) features.append(fet) pr.addFeatures( features ) vl.updateExtents() QgsMapLayerRegistry.instance().addMapLayer(vl)
Another part of the result:
Should you need attributes in the snapped routes, we could use a Spatial Index to rapidly evaluate intersections (such as in https://gis.stackexchange.com/a/130440/4972 ), but that's another story.
Hope this helps!
This was really an easy solution. I had to do spatial join with the hexagon grid layer and polygon layer (which had the residential density data). The tool join attributes by location is used.
Best Answer
You can find it in the Processing > Toolbox > search for Count Points in Polygon
Not sure why it's missing from the Vector menu...