[GRASSLIST:1115] How to make vector data network on raster map

[Hayashi Shin-ichiro]

Dear GRASS Users

I want to make vector data network on raster map
like this.
http://ryuiki.agbi.tsukuba.ac.jp/~forest/network.png

Vector data need to satisfy following condition.
1)  These are node of vector data on the point which has raster data.
2)  These is one node of vector data in the center of raster data's grid.
3)  link connects from node to node.
(Please look at my png file)

My question are
1) What command does GRASS have to make vector data which is mentioned above?
2) If GRASS has no command to make vector data which is mentioned above, 
  How way can I have?

Please give me your suggestion.
Thank you in advance.
Sincerely yours. 




----
Hayashi Shin'ichiro  
mail:forest at bres.tsukuba.ac.jp URL:http://ryuiki.agbi.tsukuba.ac.jp/~forest
Watershed Management Lab., University of TSUKUBA