[GRASS-dev] Network Analysis

[Daniel Bundala]

Hello Markus,

Thanks for the comments. I will definitely add your suggestion to the
code. I should have some time to do it this or next week.

Regarding the bug: It is definitely a bug and I will have a look at
it. But I think that it would be better if dglib supported multiple
edges between nodes. Not only it is probably intended behaviour if
there are multiple lines between nodes, but in some cases (e.g.,
v.net.flow module), you do not want the minimum but maximum cost edge.
In fact, you want all edges. There should not be any substantial
problem with multiple edges, but I am not sure whether dglib supports
them. What do you think?

Daniel

On Mon, Sep 14, 2009 at 12:31 PM, Markus Metz
<markus.metz.giswork at googlemail.com> wrote:
> Hi Daniel,
>
> nice job you did with the new network analysis modules! Obviously you have
> understood dglib, this is very good news :-) Maybe you could have a look at
> BUG2 [1] for network analysis? I have an idea but am not sure if it is
> correct. There is also a wish to have costs as type double instead of int,
> but it seems that this means a lot of modification of dglib. What do you
> think?
>
> Regarding the new modules, I have a suggestion: all modules use
>
>   nlines = Vect_get_num_lines(&In);
>   for (i = 1; i <= nlines; i++) {
>       int type = Vect_read_line(&In, Points, Cats, i);
>       ...
>   }
>
> or similiar. Vect_read_line exits with a fatal error for dead lines, adding
>
>   if (!Vect_line_alive(&In, i))
>       continue;
>
> before Vect_read_line() would avoid that. See e.g. Vect_copy_map_lines() in
> Vlib/map.c.
>
> Best,
>
> Markus M
>
> [1] https://trac.osgeo.org/grass/ticket/584
>
>
> Daniel Bundala wrote:
>>
>> Hello everyone,
>>
>> during the past few months I worked on a Google Summer of Code project
>> to extend GRASS network functionality. I sent a final summary report
>> to OSGeo GSoC mailing list. Since there are people not subscribed to
>> that mailing list who might be interested in the project, I was asked
>> to sent the report to this list and stress the paragraph on inclusion
>> into the main GRASS....
>>
>>
>>
>>
>> The goal of my project, which I have successfully accomplished, was to
>> implement modules for network analysis. This includes basic methods
>> such as: strongly and weakly connected components, minimum spanning
>> trees, bridges and articulation points as well as more complicated and
>> advanced tools for calculating maximum flow, minimum cut or
>> k-connectivity in a network. There is also a bunch of modules finding
>> shortest paths in a network. One module computes all-pairs shortest
>> paths, another finds the shortest paths between nodes and a given set
>> of features and, finally, there is a module that finds fastest paths
>> using timetables.
>> All module follow standard GRASS conventions. This holds both for the
>> code and user interface. I also tried to make the modules as flexible
>> as possible -- each of them accepts a wide range of parameters, which
>> can alter the behaviour. Moreover, the algorithms are separated from
>> the modules and stored in a library. An effect of this is that the
>> modules are mostly straightforward (only exception is v.net.timetable)
>> and consist only of reading the input, calling a few library functions
>> and writing an appropriate output. Another advantage of this approach
>> is that the “core functionality” can be reused in other modules. Much
>> more about the modules (a lot of pictures and link to code) can be
>> found at mi wiki: http://grass.osgeo.org/wiki/GSoC_Network_Analysis.
>>
>> I have learnt a lot about GRASS and its vector architecture however
>> this was my second summer working on vector modules. This was the
>> first time I really had to work with attributes data and so I have
>> learnt a lot about the data management. At the beginning, I found the
>> system with many layers and multiple categories a bit complicated but
>> in the process of developing the modules I have discovered its
>> expressiveness and enormous power.
>>
>> At the moment, my code is stored in add-ons repository. I already know
>> about several people using the modules for their work and I hope that
>> the modules will eventually be integrated into the main distribution
>> and bring eternal joy to all GRASS users.
>>
>> Finally, I want to thank my mentor (Wolf Bergenheim), OSGEO project
>> coordinator (Wolf Bergenheim) and the whole GRASS, OSGeo and Google
>> Summer of Code community for support, T-shirts and for doing a
>> wonderful job! Thanks!
>> Daniel
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>>
>>
>