[GRASS-user] Export specific shapes from a vector file

GRASS GRASS user
1

I need to export specific shapes from a grass vector file to another grass
vector file.
Also, I need to convert specific polygons from a vector grass file to a
raster grass file.
How can I do that?
Thanks, Leonidas
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2

On Mon, 2009-02-16 at 12:55 -0800, leonidas wrote:

I need to export specific shapes from a grass vector file to another grass
vector file.

v.extract in=VectorMap out=ExtractedFeatures ...
# you can use "list=" to extract specific categories (the "cat" column)
# or an SQL where clause, e.g. something like
"where='SomeColumn="SomeString"'

Also, I need to convert specific polygons from a vector grass file to a
raster grass file.

I assume by polygons you mean areas.

v.to.rast in=VectorMap out=RasterMap type=area ...
# "use=???" You need to decide which values you will assign to your
pixels.

How can I do that?
Thanks, Leonidas

Regards, Nikos

3

Thank you Niko,
well I understand the first one (using v.extract).
-Is it possible to do something like that using v.out.ogr and export to
shapefile?
-As far as concerns the second question using v.to.rast, how can I export
only specific areas using sql where clause or list for specific categories?
Thanks again, Leonidas

Nikos Alexandris wrote:

On Mon, 2009-02-16 at 12:55 -0800, leonidas wrote:

I need to export specific shapes from a grass vector file to another
grass
vector file.

v.extract in=VectorMap out=ExtractedFeatures ...
# you can use "list=" to extract specific categories (the "cat" column)
# or an SQL where clause, e.g. something like
"where='SomeColumn="SomeString"'

Also, I need to convert specific polygons from a vector grass file to a
raster grass file.

I assume by polygons you mean areas.

v.to.rast in=VectorMap out=RasterMap type=area ...
# "use=???" You need to decide which values you will assign to your
pixels.

How can I do that?
Thanks, Leonidas

Regards, Nikos

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4

On Mon, 2009-02-16 at 13:14 -0800, leonidas wrote:

Thank you Niko,
well I understand the first one (using v.extract).
-Is it possible to do something like that using v.out.ogr and export to
shapefile?

AFAIK, no. The way to do it is: v.extract + v.out.ogr

-As far as concerns the second question using v.to.rast, how can I export
only specific areas using sql where clause or list for specific categories?

Apologies, I overlooked the word "specific" before. Here (again) I think
you would need v.extract + v.to.rast. An example:

Let's say you have the CORINE map in whose attribute table you have a
column named "level3" of type integer (with a lentgh of 3) which
contains the CORINE land cover class codes (111,112,113, etc.).

And now you need to extract specific classes, that is areas with
specific "level3" codes (i.e. 111, 112, 122, 123, 141, 142). Then you
could do:

v.extract in=corine_ellas_v2 out=corine_ellas_v2_subset
where='"level3"="111" or "level3"="112" or "level3"="112" or
"level3"="122" or "level3"="123" or "level3"="141" or "level3"="142"'
--o

then

v.to.rast in=corine_ellas_v2_subset out=corine_ellas_v2_subset use=attr
column=level3

Hope that helps
Cheers, Nikos

5

Yes that was what exactly I need.Thanks again

Nikos Alexandris wrote:

On Mon, 2009-02-16 at 13:14 -0800, leonidas wrote:

Thank you Niko,
well I understand the first one (using v.extract).
-Is it possible to do something like that using v.out.ogr and export to
shapefile?

AFAIK, no. The way to do it is: v.extract + v.out.ogr

-As far as concerns the second question using v.to.rast, how can I export
only specific areas using sql where clause or list for specific
categories?

Apologies, I overlooked the word "specific" before. Here (again) I think
you would need v.extract + v.to.rast. An example:

Let's say you have the CORINE map in whose attribute table you have a
column named "level3" of type integer (with a lentgh of 3) which
contains the CORINE land cover class codes (111,112,113, etc.).

And now you need to extract specific classes, that is areas with
specific "level3" codes (i.e. 111, 112, 122, 123, 141, 142). Then you
could do:

v.extract in=corine_ellas_v2 out=corine_ellas_v2_subset
where='"level3"="111" or "level3"="112" or "level3"="112" or
"level3"="122" or "level3"="123" or "level3"="141" or "level3"="142"'
--o

then

v.to.rast in=corine_ellas_v2_subset out=corine_ellas_v2_subset use=attr
column=level3

Hope that helps
Cheers, Nikos

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6

Λεωνίδα,

you might be interested in this tutorial:
Αναπαραγωγή του χάρτη CORINE με το GRASS-GIS
(http://users.hol.gr/~dzach/tilaphos/corine_grass-gis_el.pdf)

published at http://tilaphos.blogspot.com/2009/02/gis-corine.html

Χαιρετίσματα, Νίκος

7

Thanks, very interesting and useful job,
Καλό Τσίκνισμα, Λεωνίδας:-D
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