[GRASS-user] Re: [GRASSLIST:1115] Re: layers in vector datasets

[M S]

more questions on layers (perhaps overflowing into v.patch)...

i did a v.patch of some points, street lines, and lines that connect the
points to streets.  then i did the v.clean to snap and break the new node
points.

when i query by mouse on the display, the streets from the v.patch output, i
get somethings i dont understand:

1) it doesnt seem that v.clean is doing any snapping or breaking.  i click
on a street line (in the v.patch output file) and it shows one line where
the other line feature was patched in to connect to the streets.  i would
have expected a node and a break in the line to occur?  i used v.clean with
the point and line features and a threshhold of .1.

2) in the v.patch output, when i click on the street lines, it comes up in
the FORM box (under the map, mapset, feature type, length) Layer: 1,
category: 75, Database connection not defined.  at this point i
intentionally dont have any database connections defined, as i'm just trying
to get a simple geometric network to run through v.net.steiner.

3) in the v.patch output, when i click on the lines connecting the points to
the streets, there is no information in the FORM that comes up.  I do get
the map, mapset, feature type, length).  in QGIS this shows as line feature,
layer 0.  the streets show as line feature, layer 1.

any reason why after v.patch i get the lines on different layers?


On 6/19/06, M S <mseibel at gmail.com> wrote:
>
> after i work through this problem and understand whats going on, i would
> love to add to the wiki page for arc users.  its grinding out the function
> now for v.net.steiner, with a county wide dataset for streets, and 208
> steiner points its got some computing to do!  Go GRASS & Linux!
>
> can anyone explain why one would want or use arcs on different layers in
> the same grass vector dataset?  i cant think of how this would be used.
>
>
> On 6/19/06, Hamish <hamish_nospam at yahoo.com> wrote:
> >
> > M S wrote:
> > > so you have layers that can be linked to various tables.  if one does
> > > a v.patch command and now has two "layers" of lines, how can they both
> > > be put on the same layer, or does that not even matter?  i guess its
> > > like if you have a polygon coverage in workstation.  then u can build
> > > it for lines (the .aat) and polygons (the .pat).  then u can add
> > > attributes and manipulate them for the different attribute tables.
> > > however, since u cant have various "layers" of the same datatype in a
> > > coverage, i think that is where i get confused.
> >
> >
> >
> > if you have two vectors with dissimilar tables, v.patch won't/can't do
> > it.
> >
> > The "-e" flag was recently added to v.patch to try.
> >
> > see also the v.append script on the GRASS Wiki Add-ons page:
> >    http://grass.gdf-hannover.de/wiki/GRASS_AddOns#Vector_add-ons
> >
> > v.append was written before the v.patch "-e" flag.
> >
> >
> > There's an example of a module which will result in 2 layer output, but
> > I can't remember what it is right now.
> >
> >
> > Hamish
> >
>
>
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