[GRASS-dev] v.net.alloc / v.net.iso: very long running time

GRASS GRASS developer
1

Hello,

I'm testing some of the vector network features and am confronted with an extremely long running time.

Using the North Carolina data set, I start out by adding the schools into the street network:

v.net input=streets_wake@PERMANENT points=schools_wake@PERMANENT output=streets_schools_net operation=connect alayer=1 nlayer=2 thresh=200

Then trying either

v.net.alloc input=streets_schools_net output=subnets alayer=1
nlayer=2 ccats=37,127,135,59,38-39,159

or a similar v.net.iso command, I get

Building graph...
Registering arcs...
  100%
Flattening the graph...
Graph was built
Number of centres: [7] (nlayer: [2])
Calculating costs from centres...

and then a percentage indication which stays at 0% for a very long time... I actually let the module run for a night and it still hadn't advanced much.

Cutting the network to a small region makes the programs run. So there seems to a severe efficiency problem in the algorithms used which grows very quickly with file size...

Moritz

2

On Wed, Jul 9, 2008 at 1:07 PM, Moritz Lennert
<mlennert@club.worldonline.be> wrote:

Hello,

I'm testing some of the vector network features and am confronted with an
extremely long running time.

...

and then a percentage indication which stays at 0% for a very long time... I
actually let the module run for a night and it still hadn't advanced much.

AFAIK the cache is still disabled in the graph engine (DGLib). That's why
it is so slow:
lib/vector/dglib/BUGS

http://www.nabble.com/-GRASS5--Grass-5.1's-Directed-Graph-Library-CVS-snapshot-td8581688.html#a8581693
http://www.nabble.com/v.net.path-td4210952.html#a4217671
http://www.nabble.com/-GRASS5--dgtable-vector-library-td8582331.html#a8582342

Not sure how hard it would be to fix this problem (outstanding for years
meanwhile).

Markus

3

Hi,

to memorize I have create trac ticket for that

http://trac.osgeo.org/grass/ticket/224

Martin

2008/7/9 Markus Neteler <neteler@osgeo.org>:

On Wed, Jul 9, 2008 at 1:07 PM, Moritz Lennert
<mlennert@club.worldonline.be> wrote:

Hello,

I'm testing some of the vector network features and am confronted with an
extremely long running time.

...

and then a percentage indication which stays at 0% for a very long time... I
actually let the module run for a night and it still hadn't advanced much.

AFAIK the cache is still disabled in the graph engine (DGLib). That's why
it is so slow:
lib/vector/dglib/BUGS

http://www.nabble.com/-GRASS5--Grass-5.1's-Directed-Graph-Library-CVS-snapshot-td8581688.html#a8581693
http://www.nabble.com/v.net.path-td4210952.html#a4217671
http://www.nabble.com/-GRASS5--dgtable-vector-library-td8582331.html#a8582342

Not sure how hard it would be to fix this problem (outstanding for years
meanwhile).

Markus
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