rasterize vector layer (string column)

[christophe]

hello

i would like to rasterize a vector layer i guess within: v.to.rast

but the type of the column to use in the rasterization is string not numeric.

is it possible to do it in  grass 6.4 ?

thank you

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[Markus Neteler]

On Thu, Sep 4, 2014 at 4:56 PM, christophe joey
<[hidden email]> wrote:
> hello
>
> i would like to rasterize a vector layer i guess within: v.to.rast
> but the type of the column to use in the rasterization is string not
> numeric.
>
> is it possible to do it in  grass 6.4 ?

Yes.
- use v.db.addcol to add a new numeric column
- then cast the string numbers to numeric with v.db.update:
  http://grass.osgeo.org/grass64/manuals/v.db.update.html
  --> see last example (that's for the SQLite or other true SQL
drivers only, not the DBF backend)

Markus
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[christophe]

thank you markus for the reply

well, in vector layer i don't have a field containing numbers in string field, here is my attribute table:

objectID   Type

1               A

2               A

3               B

4               A

5               C

so, i have to rasterize it using the type field wich is not numeric.

How can i do it ?

thank you

On Thu, Sep 4, 2014 at 7:00 PM, Markus Neteler <[hidden email]> wrote:

On Thu, Sep 4, 2014 at 4:56 PM, christophe joey
<[hidden email]> wrote:
> hello
>
> i would like to rasterize a vector layer i guess within: v.to.rast
> but the type of the column to use in the rasterization is string not
> numeric.
>
> is it possible to do it in  grass 6.4 ?

Yes.
- use v.db.addcol to add a new numeric column
- then cast the string numbers to numeric with v.db.update:
  http://grass.osgeo.org/grass64/manuals/v.db.update.html
  --> see last example (that's for the SQLite or other true SQL
drivers only, not the DBF backend)

Markus

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[Helmut Kudrnovsky]

christophe wrote

thank you markus for the reply

well, in vector layer i don't have a field containing numbers in string
field, here is my attribute table:

objectID   Type
1               A
2               A
3               B
4               A
5               C


so, i have to rasterize it using the type field wich is not numeric.
How can i do it ?

thank you

something like this should do it:

- use v.db.addcol to add a new numeric column (e.g. column name: typenumeric)

- use v.db.update with WHERE conditions to 'translate' e.g. all A to 1, all B to 2 and so on (e.g. v.db.update map=yourvectordata column=typenumeric value=1 where="Type =  A", v.db.update map=yourvectordata column=typenumeric value=2 where="Type = B", etc.)

- use v.to.rast to rasterize the vector and label your raster map with the type information (e.g. v.to.rast input=yourvectordata column=typenumeric labelcolumn=Type)

[Markus Neteler]

On Fri, Sep 5, 2014 at 3:00 PM, christophe joey
<[hidden email]> wrote:

> thank you markus for the reply
>
> well, in vector layer i don't have a field containing numbers in string
> field, here is my attribute table:
>
> objectID   Type
> 1               A
> 2               A
> 3               B
> 4               A
> 5               C
>
>
> so, i have to rasterize it using the type field wich is not numeric.
> How can i do it ?

You can either do it as Helmut suggested or take a look at Example 3

http://grass.osgeo.org/grass70/manuals/v.to.rast.html#examples
3. Convert a vector polygon map to raster including descriptive labels

Markus
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