[GRASS-user] Loss of data using v.net

GRASS GRASS user
1

I’m trying to build a network in GRASS in order to find the shortest path from any settlement out of 1120 (points), to one waste treatment facility out of 27 (points). I plan to use v.net.distance which is designated to this purpose, and to define source and destination points using a column called “type”. In that column I have assigned the settlements layer with the number 5 and the treatment facilities with 1.

My problem occurs when I try to create the network using v.net; If I define nodes layer (nlayer=2) to be 2, I lose all the points and can’t find it, even by using v.extract. Otherwise (when nlayer=1) the attributes describing type are being auromatically changed to 4, which is the type attribute for roads.

Since I have 1120 I find that using from_cat instead of a SQL restriction will be too hard.

Any one has an idea why I’m losing this crucial data and how can I prevent it from happening?

Thanks in advanced,

Dor

2

On Wed, Jan 23, 2013 at 8:22 PM, דור פרידמן <dof1985@gmail.com> wrote:

I'm trying to build a network in GRASS in order to find the shortest path
from any settlement out of 1120 (points), to one waste treatment facility
out of 27 (points). I plan to use v.net.distance which is designated to this
purpose, and to define source and destination points using a column called
"type". In that column I have assigned the settlements layer with the number
5 and the treatment facilities with 1.

My problem occurs when I try to create the network using v.net; If I define
nodes layer (nlayer=2) to be 2, I lose all the points and can't find it,
even by using v.extract.

What is the output of v.category op=report using the output of v.net?

Markus M

Otherwise (when nlayer=1) the attributes describing
type are being auromatically changed to 4, which is the type attribute for
roads.

Since I have 1120 I find that using from_cat instead of a SQL restriction
will be too hard.

Any one has an idea why I'm losing this crucial data and how can I prevent
it from happening?

Thanks in advanced,

Dor

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3

On 23/01/13 20:22, דור פרידמן wrote:

I'm trying to build a network in GRASS in order to find the shortest
path from any settlement out of 1120 (points), to one waste treatment
facility out of 27 (points). I plan to use v.net.distance which is
designated to this purpose, and to define source and destination points
using a column called "type". In that column I have assigned the
settlements layer with the number 5 and the treatment facilities with 1.

My problem occurs when I try to create the network using v.net
<http://v.net>; If I define nodes layer (nlayer=2) to be 2, I lose all
the points and can't find it, even by using v.extract.

What is the exact comman line for v.extract that you used ? Did you set layer=2 ?

What does v.category option=report give you on the file resulting from v.net ?

Which version of GRASS are you using ?

Otherwise (when
nlayer=1) the attributes describing type are being auromatically changed
to 4, which is the type attribute for roads.

v.net certainly should not (and AFAIK does not) change attribute data. Actually attribute data of points connected to the network with v.net operation=connect is not kept. As mentioned in the man page you have to reconnect your points to the attribute data by hand after running v.net.

Any one has an idea why I'm losing this crucial data and how can I
prevent it from happening?

It would help if you could give a reproducible case description, including data (possibly from the NC demo dataset), so that we can see exactly what is going wrong where.

Moritz

4

[please keep discussions on the mailing list]

On 23/01/13 22:23, דור פרידמן wrote:

I forgot to mention that I am using GRASS 6.4.2

These is an issue with some of the v.net.* modules (incl v.net.distance) in 6.4.2: you cannot correctly input arcs in layer 1 and nodes in layer 2. You, therefore, have to use layer 1 for everything, making sure that category values of arcs and nodes do not overlap.

I would really recommend that for serious network analysis you use grass7 in which Markus Metz has not only made the interfaces of the modules more consistent, but also increased their efficiency.

Moritz

2013/1/23 Moritz Lennert <mlennert@club.worldonline.be
<mailto:mlennert@club.worldonline.be>>

    On 23/01/13 20:22, דור פרידמן wrote:

        I'm trying to build a network in GRASS in order to find the shortest
        path from any settlement out of 1120 (points), to one waste
        treatment
        facility out of 27 (points). I plan to use v.net.distance which is
        designated to this purpose, and to define source and destination
        points
        using a column called "type". In that column I have assigned the
        settlements layer with the number 5 and the treatment facilities
        with 1.

        My problem occurs when I try to create the network using v.net
        <http://v.net>
        <http://v.net>; If I define nodes layer (nlayer=2) to be 2, I
        lose all

        the points and can't find it, even by using v.extract.

    What is the exact comman line for v.extract that you used ? Did you
    set layer=2 ?

    What does v.category option=report give you on the file resulting
    from v.net <http://v.net> ?

    Which version of GRASS are you using ?

        Otherwise (when
        nlayer=1) the attributes describing type are being auromatically
        changed
        to 4, which is the type attribute for roads.

    v.net <http://v.net> certainly should not (and AFAIK does not)
    change attribute data. Actually attribute data of points connected
    to the network with v.net <http://v.net> operation=connect is not
    kept. As mentioned in the man page you have to reconnect your points
    to the attribute data by hand after running v.net <http://v.net>.

        Any one has an idea why I'm losing this crucial data and how can I
        prevent it from happening?

    It would help if you could give a reproducible case description,
    including data (possibly from the NC demo dataset), so that we can
    see exactly what is going wrong where.

    Moritz