[GRASSLIST:550] line to area

GRASS GRASS user
1

I created a line with v.digit and I now want to convert it to an area. Seems like a simple question, but how do I do it?

Thanks,
Rich

Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich@GreenwoodMap.com
(307) 733-0203
http://www.GreenwoodMap.com

2

Thanks to Erin O'Doherty and John Dougherty for the quick replies. My mistake was that I had not labeled my area in v.digit. All I wanted was a MASK, so I wasn't thinking about labels. But v.to.rast was expecting a label.

Thanks for the help guys.
Best regards,
Rich

At 12:41 PM 6/27/2003 -0700, you wrote:

On Friday 27 June 2003 11:12, Richard Greenwood wrote:
> I created a line with v.digit and I now want to convert it to
> an area. Seems like a simple question, but how do I do it?
>
> Thanks,
> Rich
>
Rich,

You need to snap the starting and ending nodes together. I have
not had much to do with digitizing in GRASS, however, v.digit is
probably the tool to use. The snap distance should be set to
force nodes together that are within the error of the map, which
for USGS maps is 0.002. Neteler and Mitasova discuss this in
their book.

John Dougherty

Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich@GreenwoodMap.com
(307) 733-0203
http://www.GreenwoodMap.com

3

Hi,
I don't know if this could help you but I hope...

if the line is snapped on itself, try v.line2area.....
then try v.alabel to assign a category number to the area and after this try
v.to.rast...
I think this can be a solution....
bye

Ivan

Alle 00:45, sabato 28 giugno 2003, Richard Greenwood ha scritto:

Thanks to Erin O'Doherty and John Dougherty for the quick replies. My
mistake was that I had not labeled my area in v.digit. All I wanted was a
MASK, so I wasn't thinking about labels. But v.to.rast was expecting a
label.

Thanks for the help guys.
Best regards,
Rich

At 12:41 PM 6/27/2003 -0700, you wrote:
>On Friday 27 June 2003 11:12, Richard Greenwood wrote:
> > I created a line with v.digit and I now want to convert it to
> > an area. Seems like a simple question, but how do I do it?
> >
> > Thanks,
> > Rich
>
>Rich,
>
>You need to snap the starting and ending nodes together. I have
>not had much to do with digitizing in GRASS, however, v.digit is
>probably the tool to use. The snap distance should be set to
>force nodes together that are within the error of the map, which
>for USGS maps is 0.002. Neteler and Mitasova discuss this in
>their book.
>
>John Dougherty

Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich@GreenwoodMap.com
(307) 733-0203
http://www.GreenwoodMap.com

--
Ivan Marchesini
University of Perugia
Italy

4

I created a line with v.digit and I now want to convert it to an area.
Seems like a simple question, but how do I do it?

v.line2area

5

All I wanted was a MASK, so I wasn't thinking about labels.

> > I created a line with v.digit and I now want to convert it to
> > an area. Seems like a simple question, but how do I do it?

r.in.poly might be an easier way to get what you want?

Hamish

6

I have a vector point dataset (ascii XYZ, the basis of a DEM).

I'm importing into GRASS5.7 with

cat <file> | v.in.ascii -Z output=nzxyz xcol=1 ycol=2 zcol=2 catcol=0

There are about 4,000,000 XYZ points.

The vector coor file is 150Mb. GRASS is now building the topology & index.
The topo file is almost 200Mb and the sidx is at 430Mb and growing.

Is this normal? It seems very excessive for a point dataset. A spatial
index & topology make more sense for line/polygon data, with over 4x the
actual data volume to store this extra info doesn't look right somehow...

The system is a SuSE Linux 9.1 23 bit OS on A64 3500 with 1Gb memory.
Swapped out 1.4Gb & still using 800Mb main memory.

Any advice appreciated....

  Brent Wood

7

It is normal.
Spatial index is important also for points, I think. Otherwise v.distance for example
must always go through all points. Say that you have another vector with 4,000,000
and you want to find the nearst in the first one. Withou spatial index it
must do 4,000,000 x 4,000,000 checks.
Spatial index is stored as tree of boxes, 6x8 bytes each, so 430 M is possible.

Any advice appreciated....

Brent Wood wrote:

I have a vector point dataset (ascii XYZ, the basis of a DEM).

I'm importing into GRASS5.7 with

cat <file> | v.in.ascii -Z output=nzxyz xcol=1 ycol=2 zcol=2 catcol=0

There are about 4,000,000 XYZ points.

The vector coor file is 150Mb. GRASS is now building the topology & index.
The topo file is almost 200Mb and the sidx is at 430Mb and growing.

Is this normal? It seems very excessive for a point dataset. A spatial
index & topology make more sense for line/polygon data, with over 4x the
actual data volume to store this extra info doesn't look right somehow...

The system is a SuSE Linux 9.1 23 bit OS on A64 3500 with 1Gb memory.
Swapped out 1.4Gb & still using 800Mb main memory.

Any advice appreciated....

Brent Wood