Does not show shortest path in networkx (in QGIS)

[Kasun Ramanayake]

I used the following commands (in qgis console) to get the shortest path with astar algorithm. But the result shows just '[]' every time. Why was that? Please help me to find a solution to this problem.

>>> import networkx as nx
>>> G = nx.read_shp(str(iface.mapCanvas().currentLayer().source()))
>>> route = nx.shortest_path(G, G.nodes()[1], G.nodes()[10])
[]
>>> route = nx.shortest_path(G, G.nodes()[20], G.nodes()[30])
[]

[Tim Sutton]

Hi

Have you tried working through the tutorial here?

http://docs.qgis.org/1.8/en/docs/pyqgis_developer_cookbook/12_network_analysis.html

Are you trying to implement your own director pattern implementation?

Regards

Tim

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[Kasun Ramanayake]

Hi,
   I tried that tutorial.Here I wanted to use the A* algorithm since it finds the shortest path avoiding obstacles. I coded the algorithm (without using the direct command-shortest_path/astar_path) but it always shows, 'no path found' for me. Then I tried using networkx (in qgis console and in code too), and found that it returns nothing. Why is that ? Is that a problem with networkx or my layer?

Thank You

[Tim Sutton]

Hi

On Sat, May 31, 2014 at 11:30 AM, Kasun Ramanayake <kasun.ra...@gmail.com> wrote:

Hi,
   I tried that tutorial.Here I wanted to use the A* algorithm since it finds the shortest path avoiding obstacles. I coded the algorithm (without using the direct command-shortest_path/astar_path) but it always shows, 'no path found' for me. Then I tried using networkx (in qgis console and in code too), and found that it returns nothing. Why is that ? Is that a problem with networkx or my layer?

Hmm I havent tried using networkx before. Can you share your layer? Did you try using a layer imported using the InaSAFE OSM downloader tool?

Regards

Tim

 

Thank You

On Saturday, May 31, 2014 9:15:11 AM UTC+5:30, Kasun Ramanayake wrote:

I used the following commands (in qgis console) to get the shortest path with astar algorithm. But the result shows just '[]' every time. Why was that? Please help me to find a solution to this problem.

>>> import networkx as nx
>>> G = nx.read_shp(str(iface.mapCanvas().currentLayer().source()))
>>> route = nx.shortest_path(G, G.nodes()[1], G.nodes()[10])
[]
>>> route = nx.shortest_path(G, G.nodes()[20], G.nodes()[30])
[]

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[Kasun Ramanayake]

No, I jsut checked. It doesn't work for any layer. I used that popular 'jakarta jalan' layer. By the way, is there any other method I can use for this purpose?
Thank You
(I attached the layer.Can you please check whether it's working..)

On Saturday, May 31, 2014 9:15:11 AM UTC+5:30, Kasun Ramanayake wrote:

[Tim Sutton]

Hi

So I made the a simple script (using Dijkstra) which I have attached which successfully routes across the network.

Can you confirm if this works for you? (it works for me)

If it does work, do you still need to use networkx?

Regards

Tim

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[Dil]

Hi,
     I used that code earlier. It worked for me too. But I wanted to use astar algorithm, which finds path by avoiding obstacles.That's why I thought to use networkx. By the way, I found that I can make a new layer by using Geoprocessing tools->difference option. So that I can remove the obstacles or impassable ares on map.Then I could use these algorithms to find a path on new layer. Is there a way to access those Geoprocessing tools in my code?
Thank you

[Tim Sutton]

Hi

On Mon, Jun 2, 2014 at 6:08 PM, Dil <dilvit...@gmail.com> wrote:

Hi,
     I used that code earlier. It worked for me too. But I wanted to use astar algorithm, which finds path by avoiding obstacles.That's why I thought to use networkx. By the way, I found that I can make a new layer by using Geoprocessing tools->difference option. So that I can remove the obstacles or impassable ares on map.Then I could use these algorithms to find a path on new layer. Is there a way to access those Geoprocessing tools in my code?

Yes - see my reply to this thread:

https://groups.google.com/forum/?hl=en#!topic/inasafe-dev/kAM1mcht8mM

May I again cordially request that you do not post the same question to multiple lists at once - it wastes effort as multiple people end up answering the same question and threads become very hard to follow as they are spread across different lists.

Thanks!

Tim

 

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