[GRASS-user] generate a grid with sequential numbers

GRASS GRASS user
1

Hi all,
does anyone know how to generate a grid where the numbers are sequential?
i have used r.random.cells to create a grid, but grids are numbered, well, randomly.
thanx,
Janet

2

On 17/09/12 16:05, Janet Choate wrote:

Hi all,
does anyone know how to generate a grid where the numbers are sequential?
i have used r.random.cells to create a grid, but grids are numbered,
well, randomly.

Maybe r.mapcalc with a combination of the row() and col() functions ? Depending on the number of cells you have you can do something like this: row()*10000+col(). This will give you an ordered sequence, but numbers from one line to the next will have a gap. If you need perfectly sequenced numbers, I imagine it's possibly to find a formula that gives you that...

Moritz

3

On 17/09/12 17:46, Moritz Lennert wrote:

On 17/09/12 16:05, Janet Choate wrote:

Hi all,
does anyone know how to generate a grid where the numbers are sequential?
i have used r.random.cells to create a grid, but grids are numbered,
well, randomly.

Maybe r.mapcalc with a combination of the row() and col() functions ?
Depending on the number of cells you have you can do something like
this: row()*10000+col(). This will give you an ordered sequence, but
numbers from one line to the next will have a gap. If you need perfectly
sequenced numbers, I imagine it's possibly to find a formula that gives
you that...

Try

r.mapcalc sequential_grid=(row()*NumberOfColumns+col())-NumberOfColumns

You can get the number of columns in your region with g.region -p ("cols").

Moritz

4

Here you go - see screenshot:

# get rows and cols as environment variables
eval `g.region -g`
r.mapcalc "grid_seq = col() * $rows + row() + $cols - ($rows + $cols)"

d.mon x0
d.rast.num grid_seq

Markus

(attachments)

raster_grid_seq.png

5

On 17/09/12 21:32, Markus Neteler wrote:

Here you go - see screenshot:

# get rows and cols as environment variables
eval `g.region -g`
r.mapcalc "grid_seq = col() * $rows + row() + $cols - ($rows + $cols)"

This can be simplified to

r.mapcalc "grid_seq = col() * $rows + row() - $rows"

and gives you a "vertical" sequence.

My solution

r.mapcalc "grid_seq = row() * $cols + col() - $cols"

gives you a "horizontal" sequence.

I added a FAQ at http://grass.osgeo.org/wiki/Sequential_Grid.

Moritz

6

On Tue, Sep 18, 2012 at 3:11 PM, Moritz Lennert
<mlennert@club.worldonline.be> wrote:
...

I added a FAQ at http://grass.osgeo.org/wiki/Sequential_Grid.

Now we have two :slight_smile: From yesterday...
http://grass.osgeo.org/wiki/Generate_a_grid_with_sequential_numbers

Markus

7

On 18/09/12 15:14, Markus Neteler wrote:

On Tue, Sep 18, 2012 at 3:11 PM, Moritz Lennert
<mlennert@club.worldonline.be> wrote:
...

I added a FAQ at http://grass.osgeo.org/wiki/Sequential_Grid.

Now we have two :slight_smile: From yesterday...
http://grass.osgeo.org/wiki/Generate_a_grid_with_sequential_numbers

Sorry, overlooked that. I can fusion the two and redirect from one to the other, unless you have already done that :wink:

Moritz