Finding nearest neighbour along a network

Hi, Alice,

 

 

As Gio mentioned, you can use the FeatureMerger to create From-To lines for every combination of base and candidate.

 

But I'm worried that it consumes very long time and huge memory in your case, since there are 2000 bases and several thousands candidates.

 

2000 x 5000 = 10,000,000 !

 

 

If you can restrict maximum straight distance between base and candidate that should be found the shortest path, the NeighborFinder could be used to increase efficiency.

 

(1) Create points of all bases and candidates with the VertexCreator. (alternatively, you can also generate points from x and y values directly by the Excel reader parameter setting)

 

(2) Send base points to the Base port; send candidate points to the Candidate port of the NeighborFinder.

 

Maximum Distance: <maximum straight distance restriction>

 

Close Candidate List Name: <list attribute name. e.g. "_list">

 

(3) Use the ListExploder to explode Matched features (i.e. base features) on the list.

 

(4) Add a neighbor candidate point to each matched base feature with the VertexCreator, to transform them into From-To lines for the ShortestPathFinder input.

 

Mode: Add Point

 

X Value: closest_candidate_x

 

Y Value: closest_candidate_y

 

 

However, the river network should have node points that match with every base and candidate point (i.e. end nodes of From-To lines) when finding shortest paths using the ShortestPathFinder.

 

One possible way to make such a network is:

 

a. Before the step (2), snap all the base/candidate points to lines or existing nodes of the network. You can use another combination of NeighborFinder and VertexCreator to do that.

 

- Send all the points to the Base port; send river lines to the Candidate port.

 

- Set a certain maximum distance.

 

Every Matched feature (point) will have coordinate on the closest line as its attributes, named "_closest_candidate_x" and "_closest_candidate_y".

 

Then, move the point to the coordinate using the VertexCreator.

 

Mode: Replace with Point

 

X Value: _closest_candidate_x

 

Y Value: _closest_candidate_y

 

b. Send the points and the river lines to a PointOnLineOverlayer. The set of resulting lines will be a network that has the snapped base/candidate points as its nodes.

 

 

Hope this helps.

 

Takashi

hmm. I remember, when I learned about the word "several" in junior high, the English teacher said it usually indicates from 5 to 7, 8...

 

Natural language is more difficult than computer program language!

 

Anyway, it's better to avoid generating such many features as much as possible.

 

Thanks very much for all your help.  I have managed to solve the problem using various bits of what you said and some other things.  I've attached my workspace in case anyone is interested.  I've attached it as an image so don't know whether you'll be able to zoom in and view the detail.

 

 

Process as follows:

 

 

(1)  Use Densifier to create extra nodes on my river network to increase the precision of snapping

 

(2)  Use Anchored Snapper to snap both sets of monitoring sites to the river network

 

(3)  Use Point on Line Overlayer to cut river network up into lots of lines with points at ends/beginnings so works in Shortest Path Finder

 

(4)  Cut down number of potential site pairs by using Neighbor Finder and List Exploder.

 

(5) Create From-To paths for Shortest Path Finder using Vertex Creator on Closest-x and Closest-Y

 

(6) Shortest Path Calculator to identify sites that are connected via river network, Lenght Calculator to measure how long the paths are, and then a tester to identify those lines less than 1.5km.