[SoC] GRASS - Network Analysis - report

Daniel Bundala bundala at gmail.com
Fri Jul 3 18:13:17 EDT 2009

Dear List,

I have finished v.net.connectivity module this week. The module
computes the vertex connectivity of a graph (minimum cardinality set
of vertices separating two given sets of vertices of the graph). The
module also supports "node capacities". More precisely, as the edge
capacities can be specified in the min-cut problem, node capacities
are used to determine vertex connectivity. To have a better idea,
please read my last week report that also has a couple of nice images.

Also, I have done v.net.centrality module that computes several vertex
centrality measures. Namely, degree, closeness, betweenness and
eigenvector measure. Similar functionality is already present in
v.generalize module. However, this module is more general. Firstly, it
stores the measures in the database and secondly, it also takes edge
lengths/costs into the account. (v.generalize assumes edge costs to be
1). The main difference is that v.generalize computes edge centrality
measures. However, with code computing vertex measures already
available, it is easy to extend the module to compute edge measures as
well. Here is a couple of fancy pictures:
http://people.ksp.sk/~dano/grass/betw.png. The pictures show closeness
and betweenness measures respectively. The meaning of colours should
be obvious: red-"nodes in the centre according to the measure",
green-"middle", blue-"boundary".

Also, I have begun to work on v.net.distance module that will be a
hybrid of v.distance and v.net.path modules. The module will compute
the shortest path(length as well as the path itself) along the network
between a set of "to" features and every "from" feature. I hope to
finish it (early) next week, as I already know about one guy awaiting
the module.

For the blocking issues: uploading centrality measures into the
database takes an awful lot of time as I am doing it in a very naive
way... I will look more into this next week.

Finally, I apologise that this report is too late. It is already 13
minutes past midnight in my timezone....,

[1] - http://grass.osgeo.org/wiki/GSoC_Network_Analysis

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