Cannot query vector network nodes

[cmbarton]

After trying various things I can now describe more of what is happening.

Main symptom: you cannot query with a mouse (v.what) nodes on a vector network. You can only query the arcs.

Underlying issues:

In creating network nodes (v.net nodes) from an existing network map (like roads major in the nc_08 demo data), the node points get written to layer 2 and a set of arcs get written to layer 1. (I'm not sure why it is not JUST creating nodes with the v.net node operator. This may be a bug or perhaps a "feature"). No attribute info is assigned to nodes created in this way, but they must have cats stored in the vector database.

Trying to query nodes, either 1) query is still not recognizing vectors that do not have linked attribute tables (likely a problem here) and/or 2) query will not query layer 2.

So problem 1 is the creation of nodes using v.net on vector lines/boundaries. Shouldn't this just be creating nodes in layer 1 rather than nodes in layer 2 and arcs in layer 1? v.net connect should then connect nodes (i.e., points) with lines/boundaries to create a network.

Problem 2 is the inability of querying (is this a v.what or a wxgui issue?) to return information about points in layer 2 that lack an attribute table. Is this a query + layer problem, query + lack of attribute table problem or a combination of both?

The combination of problems 1 and 2 results in the inability to query nodes on a network. I'm listing this as a vector problem, but wxgui querying may also be involved.

Michael

[cmbarton]

Here is additional information.

v.net does not create an attribute table for nodes, even if they are created from a set of points that DO have an attribute table. For example (using the sc_08 demo data):

v.net input=streets_wake@grass7vect_sqlite points=firestations@grass7vect_sqlite output=firestation_network operation=connect alayer=1 nlayer=2 thresh=100

creates a network of streets and firestations. The attributes from the streets_wake file get copied over into the arcs of the new forestation_network vector network file. But the attributes from the firestations do not. This is the cause of the inability to query the nodes. If I manually run v.db.connect to connect the nodes of forestation_network to the forestations attribute table (connected to nodes in layer 2), then I CAN query the nodes.

So the main problem is in how v.net creates networks not how v.what (and wxgui) queries the network. In fact, there is no problem querying nodes in layer 2 once they have an attribute table.

BUT, querying nodes still should at least show the cat values, even if there is no attribute table. So there is still a query issue here.

Michael

[annakrat]

The query problem is known - see #1703 (the last one from the list of problems). I would prefer refactoring the raster and vector querying to trying to fix this particular case. However, it would need some time.

[mmetz]

Replying to cmbarton:

Here is additional information.

v.net does not create an attribute table for nodes, even if they are created from a set of points that DO have an attribute table.

Attached to which layer in the original input vector?

I have long thought about updating the v.net module with regard to layer management, but did not yet get to do it: for v.net, it should be possible to specify the input arc and node layer, default to 1 for each. Output arc layer is 1, output node layer is 2 (current behaviour and required by the default settings of most of the v.net.* modules). Any attribute tables attached would be copied, and the vector feature attributes changed accordingly.

creates a network of streets and firestations. The attributes from the streets_wake file get copied over into the arcs of the new forestation_network vector network file. But the attributes from the firestations do not. This is the cause of the inability to query the nodes. If I manually run v.db.connect to connect the nodes of forestation_network to the forestations attribute table (connected to nodes in layer 2), then I CAN query the nodes.

This is a problem of the wxGUI. v.what from the command line works just fine, same in the tcl/tk GUI. The wxGUI, in all versions, queries the attribute tables rather than the vector features. This is not conforming to GRASS vector design.

So the main problem is in how v.net creates networks not how v.what (and wxgui) queries the network. In fact, there is no problem querying nodes in layer 2 once they have an attribute table.

BUT, querying nodes still should at least show the cat values, even if there is no attribute table. So there is still a query issue here.

Please file a bug for the wxGUI in this regard.

Markus M

[cmbarton]

The wxGUI query issue is already known and reported.

For v.net, GRASS should be treating node creation like it treats arc creation. If the operation is "connect", then the attribute table of the input points map should be copied and connected to the nodes layer; if the operation is "nodes" than at least a minimal table with the cat value in it should be created so that node values can be added later by the user.

Michael