[GRASSLIST:6083] dissolve common boundary

GRASS GRASS user
1

Dear users,
I have a reclassified vector map which have a lot of adiacent area with
the same category number ... (no database connection... only category)
now I would like to obtain the fusion of the adiacent areas with the
same category number...
can you help me with some ideas??
thank you very much...
ivan

--
Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a
06125
Perugia (Italy)
e-mail: marchesini@unipg.it
        ivan.marchesini@gmail.com
tel: +39(0)755853760
fax: +39(0)755853756

2

I have a reclassified vector map which have a lot of adiacent area
with the same category number ... (no database connection... only
category) now I would like to obtain the fusion of the adiacent areas
with the same category number...

v.extract -d

Hamish

3

On Thu, Mar 10, 2005 at 02:43:27PM +1300, Hamish wrote:

> I have a reclassified vector map which have a lot of adiacent area
> with the same category number ... (no database connection... only
> category) now I would like to obtain the fusion of the adiacent areas
> with the same category number...

v.extract -d

Would be nice to have this a tool in v.clean (also v.reclass).

Markus

4

Dear Hamish, dear Markus...
I have still problem to dissolve boundaries...
I will try to explain better the problem...
I have a lot of areas (a reclassified landuse map) in a vector map...
some of these poligon have the same values in a column of the
database...
for example: two touching areas have the same code=31
I would like that these two ares will became one single area .... and
the same for the other touching areas which have equal code values....

I have tried
v.extract -d input=landuse output=landuse_diss type=area new=-1

but the output is exactly the same map as the input

where I'm wrong???
can you help me??
thank you very much

ivan

Il giorno gio, 10-03-2005 alle 14:43 +1300, Hamish ha scritto:

> I have a reclassified vector map which have a lot of adiacent area
> with the same category number ... (no database connection... only
> category) now I would like to obtain the fusion of the adiacent areas
> with the same category number...

v.extract -d

Hamish

--
Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a
06125
Perugia (Italy)
e-mail: marchesini@unipg.it
        ivan.marchesini@gmail.com
tel: +39(0)755853760
fax: +39(0)755853756

5

I have tried
v.extract -d input=landuse output=landuse_diss type=area new=-1

but the output is exactly the same map as the input

if you zoom in do the borders of the two areas not exactly overlap?

Hamish

6

ivan marchesini wrote:

Dear Hamish, dear Markus...
I have still problem to dissolve boundaries...
I will try to explain better the problem...
I have a lot of areas (a reclassified landuse map) in a vector map...
some of these poligon have the same values in a column of the
database...
for example: two touching areas have the same code=31
I would like that these two ares will became one single area .... and
the same for the other touching areas which have equal code values....

I have tried v.extract -d input=landuse output=landuse_diss type=area new=-1

"new Enter -1 to keep original category ..."

How do you want to dissolve the boundaries and keep different categories?

Radim

but the output is exactly the same map as the input

where I'm wrong???
can you help me??
thank you very much

ivan

Il giorno gio, 10-03-2005 alle 14:43 +1300, Hamish ha scritto:

I have a reclassified vector map which have a lot of adiacent area
with the same category number ... (no database connection... only
category) now I would like to obtain the fusion of the adiacent areas
with the same category number...

v.extract -d

Hamish

7

On Thu, March 10, 2005 19:56, ivan marchesini said:

Dear Hamish, dear Markus...
I have still problem to dissolve boundaries...
I will try to explain better the problem...
I have a lot of areas (a reclassified landuse map) in a vector map...
some of these poligon have the same values in a column of the
database...
for example: two touching areas have the same code=31
I would like that these two ares will became one single area .... and
the same for the other touching areas which have equal code values....

I have tried
v.extract -d input=landuse output=landuse_diss type=area new=-1

but the output is exactly the same map as the input

where I'm wrong???
can you help me??

It dissolves, if the category values are equal, not any value in the attribute
table. So, you will first have to use v.reclass with the 'column' option to
take new category values from the desired column and then v.extract -d on the
resulting map.

Moritz

8

Dear all...
I try to answer all your questions and remarks...

-The areas are obtained from overlay operations and are perfectly
overlapping (also zooming in....)

- I have tried to search the "column" option in v.category, but I didn't
find it

- I didn't understand how the new parameter works... if I put new=1 the
table is not created... and if I put new=1 the original category are
mantained (boundary not dissolved)... which value is better???

how can I solve the problem???

thank you very much...

ivan

Il giorno ven, 11-03-2005 alle 10:28 +0100, Moritz Lennert ha scritto:

On Thu, March 10, 2005 19:56, ivan marchesini said:
> Dear Hamish, dear Markus...
> I have still problem to dissolve boundaries...
> I will try to explain better the problem...
> I have a lot of areas (a reclassified landuse map) in a vector map...
> some of these poligon have the same values in a column of the
> database...
> for example: two touching areas have the same code=31
> I would like that these two ares will became one single area .... and
> the same for the other touching areas which have equal code values....
>
> I have tried
> v.extract -d input=landuse output=landuse_diss type=area new=-1
>
>
> but the output is exactly the same map as the input
>
> where I'm wrong???
> can you help me??

It dissolves, if the category values are equal, not any value in the attribute
table. So, you will first have to use v.reclass with the 'column' option to
take new category values from the desired column and then v.extract -d on the
resulting map.

Moritz

--
Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a
06125
Perugia (Italy)
e-mail: marchesini@unipg.it
        ivan.marchesini@gmail.com
tel: +39(0)755853760
fax: +39(0)755853756

9

On Fri, March 11, 2005 12:49, ivan marchesini said:

Dear all...
I try to answer all your questions and remarks...

-The areas are obtained from overlay operations and are perfectly
overlapping (also zooming in....)

- I have tried to search the "column" option in v.category, but I didn't
find it

v.reclass, not v.category

- I didn't understand how the new parameter works... if I put new=1 the
table is not created... and if I put new=1 the original category are
mantained (boundary not dissolved)... which value is better???

how can I solve the problem???

thank you very much...

ivan

Il giorno ven, 11-03-2005 alle 10:28 +0100, Moritz Lennert ha scritto:

On Thu, March 10, 2005 19:56, ivan marchesini said:
> Dear Hamish, dear Markus...
> I have still problem to dissolve boundaries...
> I will try to explain better the problem...
> I have a lot of areas (a reclassified landuse map) in a vector map...
> some of these poligon have the same values in a column of the
> database...
> for example: two touching areas have the same code=31
> I would like that these two ares will became one single area .... and
> the same for the other touching areas which have equal code values....
>
> I have tried
> v.extract -d input=landuse output=landuse_diss type=area new=-1
>
>
> but the output is exactly the same map as the input
>
> where I'm wrong???
> can you help me??

It dissolves, if the category values are equal, not any value in the
attribute
table. So, you will first have to use v.reclass with the 'column' option to
take new category values from the desired column and then v.extract -d on
the
resulting map.

Moritz

--
Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a
06125
Perugia (Italy)
e-mail: marchesini@unipg.it
        ivan.marchesini@gmail.com
tel: +39(0)755853760
fax: +39(0)755853756

10

Sorry moritz,
I have just seen that you said v.reclass....
yes... I did this....
and I obtained a map where, if I ask with d.what.vect, I obtain only:

map: 'prova'
mapset: 'provincia'
feature type: Centroid

Layer: 1
category: 31
Database connection not defined

I think it is good for v.extract -d !!!!

Then I have tryed to execute v.extraxt -d

v.extract -d input=prova output=prova_diss type=area

and all is working very well!!!!!!!

thank you to all....
ivan

Il giorno ven, 11-03-2005 alle 10:28 +0100, Moritz Lennert ha scritto:

On Thu, March 10, 2005 19:56, ivan marchesini said:
> Dear Hamish, dear Markus...
> I have still problem to dissolve boundaries...
> I will try to explain better the problem...
> I have a lot of areas (a reclassified landuse map) in a vector map...
> some of these poligon have the same values in a column of the
> database...
> for example: two touching areas have the same code=31
> I would like that these two ares will became one single area .... and
> the same for the other touching areas which have equal code values....
>
> I have tried
> v.extract -d input=landuse output=landuse_diss type=area new=-1
>
>
> but the output is exactly the same map as the input
>
> where I'm wrong???
> can you help me??

It dissolves, if the category values are equal, not any value in the attribute
table. So, you will first have to use v.reclass with the 'column' option to
take new category values from the desired column and then v.extract -d on the
resulting map.

Moritz

--
Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a
06125
Perugia (Italy)
e-mail: marchesini@unipg.it
        ivan.marchesini@gmail.com
tel: +39(0)755853760
fax: +39(0)755853756