[GRASSLIST:9593] Re: v.buffer: area boundary around line? Wanted: howto!

[Otto Dassau]

Am Mittwoch, 21. Dezember 2005 15:17 schrieb Wolfgang Qual:
> Hello Otto,
> so you do not have the possibility to choose layer property "1_polygon" in
> the "add grass vector layer dialog" of QGIS? I just tried the same command
> (v.buffer in=roads out=roadsbuf buffer=20) and it looks ok. If I choose
> 0_polygon, only the area between the roads is drawn by QGIS.

Hi 

Sorry - I didn't use QGIS but GRASS to visualize the resulting map. QGIS 
visualizes those data differently. In GRASS the closed lines are displayed as 
an area but only exist as a boundary without any information. 

Some time ago there was a discussion about when to display a closed line as an 
area and when not. I still do not know (don't remember), why in GRASS those 
closed boundaries, in my opinion no areas, are displayed. 

Can someone help out again and explain? I think there was a good reason for 
this - right?

  thanks
   Otto

> Best regards,
> Wolfgang
>
>
> -----
>
> > --- Ursprüngliche Nachricht ---
> > Von: Otto Dassau <dassau at gdf-hannover.de>
> > An: "Wolfgang Qual" <Wolfgang.Qual at gmx.net>
> > Kopie: grasslist at baylor.edu
> > Betreff: [GRASSLIST:9591] Re: v.buffer: area boundary around line?
> > Wanted: howto!
> > Datum: Wed, 21 Dec 2005 13:45:47 +0100
> >
> > Am Mittwoch, 21. Dezember 2005 13:19 schrieb Wolfgang Qual:
> > > Hi Otto, hi list.
> >
> > Hi,
> >
> > the problems I described still exist with the spearfish dataset:
> >
> > v.buffer in=roads out=roadsbuf buffer=20 type=line
> > v.buffer in=roads out=roadsbuf buffer=20
> >
> > it doesn't make a difference in the result.
> >
> >   Otto
> >
> > > Sorry, I think I was too fast...:
> > > If I *do not specify "type"* in the command for v.buffer (v.buffer
> > > in=ausschnitt out=buff_ausschnitt bufcol=gesamtbr)
> > > I do get a correct result. I can add this vector to my QGIS-Map (Layer
> > > 1_polygon) - works.
> > > However: how can I display this in GRASS (d.mon, d.vect)? If I try
> >
> > d.vect,
> >
> > > the area inside the ring is also displayed!
> > >
> > > Wolfgang
> > >
> > > Buffer is drawn around the feature (line).
> > >
> > > > --- Ursprüngliche Nachricht ---
> > > > Von: Otto Dassau <dassau at gdf-hannover.de>
> > > > An: "Wolfgang Qual" <Wolfgang.Qual at gmx.net>
> > > > Kopie: grasslist at baylor.edu
> > > > Betreff: Re: [GRASSLIST:9588] v.buffer: area boundary around line?
> > > > Wanted: howto!
> > > > Datum: Wed, 21 Dec 2005 12:17:50 +0100
> > > >
> > > > Am Mittwoch, 21. Dezember 2005 11:22 schrieb Wolfgang Qual:
> > > > > Hi List,
> > > >
> > > > Hi,
> > > >
> > > > > I tried to create a new area boundary around a line theme. Thought
> >
> > it
> >
> > > > would
> > > >
> > > > > be easy to do it like this:
> > > > >
> > > > > v.buffer in=ausschnitt out=buff_ausschnitt bufcol=gesamtbr
> > > > > type=boundary
> > > >
> > > > I also tried with the spearfish location and a CVS snapshot from
> > > > today and got
> > > > similar strange results, where the lines (roads) describe a closed
> >
> > ring.
> >
> > > > v.buffer in=roads out=roadsbuf buffer=20 type=line
> > > >
> > > >
> > > >   Otto
> > > >
> > > > > But GRASS won't create a new theme. After that, I tried to first
> >
> > create
> >
> > > > a
> > > >
> > > > > line buffer theme (works fine) and then convert it to a area
> >
> > boundary
> >
> > > > theme
> > > >
> > > > > using v.type. However, the new area boundary theme does not have
> > > > > the
> > > >
> > > > shape
> > > >
> > > > > of the line buffer theme.
> > > > >
> > > > > BTW, the line theme looks like this (street network):
> > > > >
> > > > >   ------------------
> > > > >
> > > > >     |         |       ...but I get s.th.      XXXXXXXXXXXX
> > > > >     |         |       like this:              XXXXXXXXXXXX
> > > > >
> > > > >   --------------                              XXXXXXXXXXXX (area
> > > > > inside)
> > > > >
> > > > > I would greatly appreciate to receive some hints...
> > > > >
> > > > >
> > > > > Best wishes,
> > > > > Wolfgang
> > > >
> > > > --
> > > > GDF Hannover - Solutions for spatial data analysis and remote sensing
> > > > Office Hannover     -      Mengendamm 16d    -     D - 30177 Hannover
> > > > Internet: www.gdf-hannover.de,               Email:
> >
> > info at gdf-hannover.de
> >
> > > > Phone : ++49.(0)511.39088507,              Fax: ++49.(0)511.39088508
> >
> > --
> > GDF Hannover - Solutions for spatial data analysis and remote sensing
> > Office Hannover     -      Mengendamm 16d    -     D - 30177 Hannover
> > Internet: www.gdf-hannover.de,               Email: info at gdf-hannover.de
> > Phone : ++49.(0)511.39088507,              Fax: ++49.(0)511.39088508

-- 
GDF Hannover - Solutions for spatial data analysis and remote sensing
Office Hannover     -      Mengendamm 16d    -     D - 30177 Hannover
Internet: www.gdf-hannover.de,               Email: info at gdf-hannover.de
Phone : ++49.(0)511.39088507,              Fax: ++49.(0)511.39088508