[GRASS-user] Create a raster starting from a coordinate pair

GRASS GRASS user
1

Hi all,
is there some grass raster command to create a raster starting from a
coordinate pair?

Something like r.createraster input=x,y output=myraster

Thank you,

Andrea

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2

What do you mean exactly with creating a raster from a coordinate pair?

If you want to align a raster to your coordinates you might have a look into g.region
and set appropriate resolution and extend coordinates.

To create a raster based on coordinates, eg. set a raster value at a specific coordinate
pair to a specific value you could use r.mapcalc:

E.g. Set the value 1 at the cell x=52, y=10
r.mapcalc “newmap = if(abs(x()-52.0)<0.001 && abs(y()-10.00)<0.001, 1)”

If you know the specific row and column and resolution you could also use:
r.mapcalc “newmap = if(row()-1 == int(($n-10.0)/$nsres) && col()-1 == int((52.0-$w)/$ewres), 1)”

Thanks to Glynn who taught me these things some time ago on the mailing list :slight_smile:

/Johannes

···

On Tue, Dec 10, 2013 at 1:02 PM, aborruso <aborruso@gmail.com> wrote:

Hi all,
is there some grass raster command to create a raster starting from a
coordinate pair?

Something like r.createraster input=x,y output=myraster

Thank you,

Andrea

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3

Hi Johannes,
thank you.

Johannes Radinger wrote

What do you mean exactly with creating a raster from a coordinate pair?

You are rigth, I have to be more understandable.

I have defined region, with a defined extent and a defined resolution.
Starting from a coordinate pair I would like to create a boolean raster
(with the same extent and resolution of my region) that "register" my pair
(in example 1 for my pixel and 0 for all the rest).

Best regards,

Andrea

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4

Hi Andrea,
may be you need something like that:
http://grass.osgeo.org/grass65/manuals/r.in.xyz.html

I'm not sure if that was the problem.

all the best

Ivan

On Tue, 2013-12-10 at 05:01 -0800, aborruso wrote:

Hi Johannes,
thank you.

Johannes Radinger wrote
> What do you mean exactly with creating a raster from a coordinate pair?

You are rigth, I have to be more understandable.

I have defined region, with a defined extent and a defined resolution.
Starting from a coordinate pair I would like to create a boolean raster
(with the same extent and resolution of my region) that "register" my pair
(in example 1 for my pixel and 0 for all the rest).

Best regards,

Andrea

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5

Ciao Ivan,
thank you.

ivan.marchesini wrote

may be you need something like that:
http://grass.osgeo.org/grass65/manuals/r.in.xyz.html

Not exactly. I would like to use as inpunt only a coordinate pair and not
another file.

Best regards

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6

Here a short example for a subregion of the North Carolina Sample Dataset with resolution 10x10 m

g.region -p
projection: 99 (Lambert Conformal Conic)
zone: 0
datum: nad83
ellipsoid: a=6378137 es=0.006694380022900787
north: 224820
south: 224450
west: 641120
east: 641660
nsres: 10
ewres: 10
rows: 37
cols: 54
cells: 1998

When I run following command I get a raster map with the value 1 for the coordinate pair 641335.0/224515.00 (cell center). All other cell have the value 0.

r.mapcalc “newmap = if(abs(x()-641335.0)<0.001 && abs(y()-224515.00)<0.001, 1, 0)”

/Johannes

···

On Tue, Dec 10, 2013 at 2:21 PM, Ivan Marchesini <ivan.marchesini@gmail.com> wrote:

Hi Andrea,
may be you need something like that:
http://grass.osgeo.org/grass65/manuals/r.in.xyz.html

I’m not sure if that was the problem.

all the best

Ivan

On Tue, 2013-12-10 at 05:01 -0800, aborruso wrote:

Hi Johannes,
thank you.

Johannes Radinger wrote

What do you mean exactly with creating a raster from a coordinate pair?

You are rigth, I have to be more understandable.

I have defined region, with a defined extent and a defined resolution.
Starting from a coordinate pair I would like to create a boolean raster
(with the same extent and resolution of my region) that “register” my pair
(in example 1 for my pixel and 0 for all the rest).

Best regards,

Andrea

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7

Hi Johannes,
thank you, thank you, thank you.

I'll try

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8

On 10/12/13 14:44, aborruso wrote:

Hi Johannes,
thank you, thank you, thank you.

Another solution:

- create a vector point with v.in.ascii or v.edit
- transform that into a raster with v.to.rast

Moritz

9

On Tue, Dec 10, 2013 at 1:02 PM, aborruso <aborruso@gmail.com> wrote:

Hi all,
is there some grass raster command to create a raster starting from a
coordinate pair?

Something like r.createraster input=x,y output=myraster

Hi Andrea,

maybe this comes pretty close:
http://grass.osgeo.org/grass64/manuals/r.in.poly.html

Markus