[GRASS-user] Grass Graphic Model v.net.distance Not Accepting point layer in From or To fields

Moritz Lennert mlennert at club.worldonline.be
Sun Nov 21 23:32:24 PST 2021

Hi Joshua,

Le 21 novembre 2021 22:12:42 GMT+01:00, Joshua Geoghegan <joshua.geoghegan at mornpen.vic.gov.au> a écrit :
>Hi there,
>I have been stuck on a problem and I was hoping you could help, as I had no luck on GIS Stack Exchange.
>I have a point and network layer connected in Grass GIS via the graphic modeler.

What exactly do you mean by 'the graphic modeler'. I assume you connect the two using v.net ? 

> I am trying to find the shortest path between the first point (ROUND=0) and every other point (ROUND != 0) on the same point layer. For some reason I can select this layer (layer 2) in both From and To tabs and add category 1-500 (which is more than the number of points), but when I try the where clause and test for values in the ROUND field on the SQL Builder the results show up as '', even though the imported shp file has values. When I hit OK and come back into the form it has reverted back to layer 1 in the From and To tabs, which is road network layer.
>What could be the issue here?

As the v.net man page states: "While the arcs created with v.net will retain any attribute information associated with the input vector line/boundary file in data layer 1, nodes created and stored in data layer 2 will not have any associated attribute information."

You have two options:

1) Find out what to the category number of the point is that has ROUND=0 and use that as from_cats, and all the others as to_cats.

This could be done with v.db.select using columns=cat (assuming the column containing the cat values is called 'cat') and where=ROUND=0.

2) Connect the attribute table of your original point map to the point layer of the connected network map using v.db.connect and the use the from_where and to_where parameters as you did.

If any of that is not clear, don't hesitate to come back to us.


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