Using PyQGIS, I desperately need help on creating a buffer around a point in a node layer and then selecting features from a trails layer that fall within the buffer. When I load the shape files without OpenLayers, it works. If I load a base map from OpenLayers like Bing Aerial or Google Satellite, the buffer no longer finds any features from the trails layer.
Also, zoom to location works great without OpenLayers, but when I bring in the map, it zooms in so far that all I see is a blank screen, and I have to manually zoom out quite a bit to see the shape files.
The base map is critical for the project or I would just do without.
Here is the code for selecting the trail features within the node buffer. If the feature we are looking for is not part of the selection, the code then zooms to the buffer bounding box around the node so the user can manually select a new trail. The base map is necessary in order to manually make a proper selection.
def check_trail(self, node_id):
# Check if trail record has changed.
found = 0
canvas = self.iface.mapCanvas()
request = QgsFeatureRequest().setFilterFid(node_id)
feature = self.nodes_layer.getFeatures(request).next()
pntGeom = feature.geometry()
pntBuf = pntGeom.buffer(canvas.mapUnitsPerPixel()*30, 0)
rect = pntBuf.boundingBox()
# Convert the rectangle coordinates to the layer CRS.
layerRect = canvas.mapRenderer().mapToLayerCoordinates(self.trailfile, rect)
# save currently select trailfile
trail_current = self.trailfile.selectedFeaturesIds()
# remove current trailfile selection
self.trailfile.removeSelection()
# Select the features that are in the rectangle and return their fids.
self.trailfile.select(layerRect, False)
# get selected trails
trails_found = self.trailfile.selectedFeaturesIds()
for trail in trails_found:
self.trailfile.removeSelection()
self.trailfile.select(trail)
temp_trail_name = self.trailfile.selectedFeatures()[0].attribute('name')
# compare buffered trail name with the most recent trail name obtained
if temp_trail_name == self.trails[-1]["name"]:
# add trail
found = -1
break
if not found:
# Zoom to location where there is a new trail
self.trailfile.removeSelection()
selectList=[node_id]
self.nodes_layer.setSelectedFeatures(selectList)
box = self.nodes_layer.boundingBoxOfSelected()
self.iface.mapCanvas().setExtent(box)
self.iface.mapCanvas().refresh()
self.trailfile.select(trail_current)
# select trail to attach to segment
while not self.selectFeatureResult and not self.cancelProdUnits:
# Set the canvas click response to select a trail.
self.clickResponse = select_trail
self.selectTrail.show()
self.selectTrail.exec_()
self.selectFeatureResult = 0
