为QGIS 2空间连接（PyQGIS）创建空间索引

Question

I've written a bit of code to do a simple spatial join in QGIS 2 and 2.2 (points that lie within a buffer to take attribute of the buffer). However, I'd like to employ a QgsSpatialIndex in order to speed things up a bit. Where can I go from here:

pointProvider = self.pointLayer.dataProvider()
rotateProvider = self.rotateBUFF.dataProvider()

all_point = pointProvider.getFeatures()
point_spIndex = QgsSpatialIndex()
for feat in all_point:
    point_spIndex.insertFeature(feat)

all_line = rotateProvider.getFeatures()
line_spIndex = QgsSpatialIndex()
for feat in all_line:
    line_spIndex.insertFeature(feat)

rotate_IDX = self.rotateBUFF.fieldNameIndex('bearing')
point_IDX = self.pointLayer.fieldNameIndex('bearing')

self.pointLayer.startEditing()
for rotatefeat in self.rotateBUFF.getFeatures():
    for pointfeat in self.pointLayer.getFeatures():
        if pointfeat.geometry().intersects(rotatefeat.geometry()) == True:
            pointID = pointfeat.id()
bearing = rotatefeat.attributes()[rotate_IDX]
self.pointLayer.changeAttributeValue(pointID, point_IDX, bearing)
self.pointLayer.commitChanges()

Answer 1

To do this kind of spatial join, you can use the QgsSpatialIndex ( http://www.qgis.org/api/classQgsSpatialIndex.html ) intersects(QgsRectangle) function to get a list of candidate featureIDs or the nearestNeighbor (QgsPoint,n) function to get the list of the n nearest neighbours as featureIDs.

Since you only want the points that lie within the buffer, the intersects function seems most suitable. I have not tested if a degenerate bbox (point) can be used. If not, just make a very small bounding box around your point.

The intersects function returns all features that have a bounding box that intersects the given rectangle, so you will have to test these candidate features for a true intersection.

Your outer loop should be on the points (you want to to add attribute values to each point from their containing buffer).

# If degenerate rectangles are allowed, delta could be 0,
# if not, choose a suitable, small value
delta = 0.1
# Loop through the points
for point in all_point:
    # Create a search rectangle
    # Assuming that all_point consist of QgsPoint
    searchRectangle = QgsRectangle(point.x() - delta, point.y()  - delta, point.x() + delta, point.y() + delta)
    # Use the search rectangle to get candidate buffers from the buffer index
    candidateIDs = line_index.intesects(searchRectangle)
    # Loop through the candidate buffers to find the first one that contains the point
    for candidateID in candidateIDs:
        candFeature == rotateProvider.getFeatures(QgsFeatureRequest(candidateID)).next()
        if candFeature.geometry().contains(point):
            # Do something useful with the point - buffer pair

            # No need to look further, so break
            break