[SoC] GRASS - Network Analysis, 1st week report

Helena Mitasova hmitaso at unity.ncsu.edu
Sat May 16 19:47:18 EDT 2009

Hi Daniel,

welcome back!

Thanks for the feedback about the street and railroad data.
In fact, these data sets are updated every 6 months by law and Wake  
provides monthly updates - the latest has been posted April 29 and it  
looks like
the errors have been fixed.
The roadsmajor is just for orientation and the errors seem to be  
leftover segments of removed
roads. More detailed streets_wake should be better, but still can  
have some errors.

In the latest data set for major roads the interchanges have been  
removed and the data set seems to be pretty clean
(note that it is in feet)

Wake_streets has all the details with updates.

I can prepare a new release of the data set as nc_spm_09 (and the  
smaller nc_basic as well), if it would be worth the effort
(the data need to be projected/transformed from feet and clipped and  
above all tested at least with the GRASSbook examples
to make sure GRASS can handle whatever is in the updated data sets).

There are also LRS roads and integrated statewide road data from  
Department of Transportation
  that should be cleaned up and properly structured for routing

Railroad data might have been updated too - I haven't looked at them  

I am posting this to the developers list as well to get some feedback  
on whether
it  would be worth the effort to update the data set (there is huge  
amount of free data available and easy to get
from nconemap.com in case somebody wants them but I am not sure we  
need them in the data set so
I suggest to limit the update to fixing errors and adding more  
specific metadata links),


Helena Mitasova
Associate Professor
Department of Marine, Earth
and Atmospheric Sciences
1125 Jordan Hall, Campus Box 8208
North Carolina State University
Raleigh NC 27695-8208

On May 15, 2009, at 4:25 PM, Markus Neteler wrote:

> On Fri, May 15, 2009 at 10:15 PM, Daniel Bundala  
> <bundala at gmail.com> wrote:
>> Hello list,
>> I have agreed with my mentor, Wolf, to start working on my GSoC
>> project bit earlier so that I can concentrate more on the exams  
>> later.
>> Well, earlier means last Saturday and so this is my first week  
>> report.
>> Just a short introduction: I am Daniel, 3rd year at Oxford doing
>> Mathematics and Computer Science and some of you may remember me as
>> the student working on GRASS v.generalize module two years ago. My
>> project this year is about extending GRASS network/vector
>> functionality by writing a couple of modules. I have created a wiki
>> page: http://grass.osgeo.org/wiki/GSoC_Network_Analysis, which
>> contains some useful information such as this email and a link to the
>> abstract.
>> Anyway, after doing boring, but essential, tasks such as downloading
>> and compiling GRASS (I use 6.4 developer branch) I have done more
>> interesting stuff. I wrote a module for computing weakly and strongly
>> connected components. Using this module, I found errors in the
>> standard North Caroline datset. At least, I think that these are
>> errors. For example, if you zoom to [north: 232051.61663403  south:
>> 230521.9965903  east: 640369.10332306  west: 638669.65919416] and let
>> GRASS draw roadsmajor map for you, you get something like this:
>> http://people.ksp.sk/~dano/grass/wcc1.jpg. (colours correspond to
>> different components, which I obtained using my module). Or, the same
>> map, but different location [north: 239329.55684214  south:
>> 238882.80682937  east: 630466.77182694  west: 629997.32746966], and
>> you have another disconnected lines:
>> http://people.ksp.sk/~dano/grass/wcc2.jpg
>> Then, I have also written a module for computing bridges(edges whose
>> removal disconnects the graph) in the network and found another,
>> probably error. This time, it is in map "railroads". The location is
>> [north: 195851.98992388  south: 187604.09950596  east:  
>> 669691.16599023
>>  west: 663129.724274] and the picture is:
>> http://people.ksp.sk/~dano/grass/railroads.jpg. Note that the lines
>> are not connected at the point the red arrow points at. Also, it
>> seems, but I am not completely sure, that there is something wrong
>> with the red segment the green arrow points at. I think, that the
>> segment is not topologically connected to the network at both ends,
>> although, visually, it seems that it is.
> That's great - this tool will help a lot.
> Concerning the North Caroline dataset (I am coauthor [1])
> just the note that this are official governmental data...!
> Perhaps we can fix them in a future release of this dataset package.
> [1] http://www.grassbook.org/data_menu3rd.php  (NC in GRASS format)
>      http://grass.osgeo.org/download/data.php (NC Subsets and in
> common GIS formats)
>> Finally, here is a random picture from a module for computing  
>> bridges:
>> http://people.ksp.sk/~dano/grass/bridges.jpg. (The data is from
>> streets_wake map). The red edges are bridges. Strictly speaking, the
>> blue edges are bridges as well, but they are not the type of bridge
>> you usually look for/consider important. So I wrote another module
>> that can identify such chains hanging on the network and remove them.
>> The code should appear shortly in GRASS addons repository.
>> That is for the last week. I am not currently stuck at anything and I
>> plan to develop another modules over the next week. For exampe,  
>> module
>> for computing articulation points as the algorithm is almost the same
>> as for bridges.
> Excellent - please keep up the good work!
> Best,
> Markus

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