[GRASS-user] Raster addition

GRASS GRASS user
1

Hello.

I am trying to add some raster maps. I thought I could do this in r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where the maps overlap and ignoring areas where only on of the maps have values. I would like to do something similar to "v.overlay operator=or".

Anyone who knows how to do this?

Martin Ytre-Eide

2

On 14/04/11 13:54, Martin Album Ytre-Eide wrote:

Hello.

I am trying to add some raster maps. I thought I could do this in
r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where
the maps overlap and ignoring areas where only on of the maps have
values.

This is due to the way r.mapcalc handles NULL values. See the man page, section NULL support for an explanation.

I would like to do something similar to "v.overlay
operator=or".

Anyone who knows how to do this?

It depends on what you want the new map to contain as values. If you want to add the value of old_1 to old_2 in places where they overlap, one way would be to transform your null values to 0 using r.null null= and then applying your formula.

If you just want a (any) value where one of the maps is non-null, then you can use if. Something like this (untested):

new_map = if(!isnull(old_1) || !isnull(old_2), 1, null())

which should give you 1 where any of the two contains a value and a NULL value elsewhere.

Moritz

3

I would like the NULL values that overlap with none NULL values to be treated as 0, and still have NULL values where both maps have NULL values. The combined map would be a large map with NULL values and added values.

Maybe the best way is to use r.null and set NULL values to 0. Add the maps and then convert the 0 values to NULL values?
Or could one set the value in the if statement to be a the sum of maps somehow? I guess my biggest problem is summing with NULL values - maybe there is a way to treat NULL values as 0? I'll have a look at the man page

Thanks,

Martin

-----Opprinnelig melding-----
Fra: Moritz Lennert [mailto:mlennert@club.worldonline.be]
Sendt: 14. april 2011 14:15
Til: Martin Album Ytre-Eide
Kopi: grass-user@lists.osgeo.org
Emne: Re: [GRASS-user] Raster addition

On 14/04/11 13:54, Martin Album Ytre-Eide wrote:

Hello.

I am trying to add some raster maps. I thought I could do this in
r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where
the maps overlap and ignoring areas where only on of the maps have
values.

This is due to the way r.mapcalc handles NULL values. See the man page, section NULL support for an explanation.

I would like to do something similar to "v.overlay operator=or".

Anyone who knows how to do this?

It depends on what you want the new map to contain as values. If you want to add the value of old_1 to old_2 in places where they overlap, one way would be to transform your null values to 0 using r.null null= and then applying your formula.

If you just want a (any) value where one of the maps is non-null, then you can use if. Something like this (untested):

new_map = if(!isnull(old_1) || !isnull(old_2), 1, null())

which should give you 1 where any of the two contains a value and a NULL value elsewhere.

Moritz

4

On 14/04/11 14:31, Martin Album Ytre-Eide wrote:

I would like the NULL values that overlap with none NULL values to be
treated as 0, and still have NULL values where both maps have NULL
values. The combined map would be a large map with NULL values and
added values.

Maybe the best way is to use r.null and set NULL values to 0. Add the
maps and then convert the 0 values to NULL values?

I think this is probably the easiest.

Or could one set
the value in the if statement to be a the sum of maps somehow? I
guess my biggest problem is summing with NULL values - maybe there is
a way to treat NULL values as 0? I'll have a look at the man page

If you chose to do it all directly in r.mapcalc, then I guess the only option is nested if statements

new_map = if(!isnull(old_1) && !isnull(old_2), old_1+old_2, if(!isnull(old_1) && isnull(old_2), old_1, etc)

Moritz

Thanks,

Martin

-----Opprinnelig melding----- Fra: Moritz Lennert
[mailto:mlennert@club.worldonline.be] Sendt: 14. april 2011 14:15
Til: Martin Album Ytre-Eide Kopi: grass-user@lists.osgeo.org Emne:
Re: [GRASS-user] Raster addition

On 14/04/11 13:54, Martin Album Ytre-Eide wrote:

Hello.

I am trying to add some raster maps. I thought I could do this in
r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map
where the maps overlap and ignoring areas where only on of the maps
have values.

This is due to the way r.mapcalc handles NULL values. See the man
page, section NULL support for an explanation.

I would like to do something similar to "v.overlay operator=or".

Anyone who knows how to do this?

It depends on what you want the new map to contain as values. If you
want to add the value of old_1 to old_2 in places where they overlap,
one way would be to transform your null values to 0 using r.null
null= and then applying your formula.

If you just want a (any) value where one of the maps is non-null,
then you can use if. Something like this (untested):

new_map = if(!isnull(old_1) || !isnull(old_2), 1, null())

which should give you 1 where any of the two contains a value and a
NULL value elsewhere.

Moritz

5

-------- Original-Nachricht --------

Datum: Thu, 14 Apr 2011 14:31:32 +0200
Von: Martin Album Ytre-Eide <Martin.Album.Ytre-Eide@nrpa.no>
An: \'Moritz Lennert\' <mlennert@club.worldonline.be>
CC: "grass-user@lists.osgeo.org" <grass-user@lists.osgeo.org>
Betreff: SV: [GRASS-user] Raster addition

I would like the NULL values that overlap with none NULL values to be
treated as 0, and still have NULL values where both maps have NULL values. The
combined map would be a large map with NULL values and added values.

that is possible with the r.mapcalc and a if condition like:

if(map A &&& map B, 0, null())

something like that (untested) might work. the null () provides NULL values where the condition is false. The triple &&& is the logic and (treats NULL values different from double &&).

see: http://grass.fbk.eu/gdp/html_grass64/r.mapcalc.html for more information.

/j

Maybe the best way is to use r.null and set NULL values to 0. Add the maps
and then convert the 0 values to NULL values?
Or could one set the value in the if statement to be a the sum of maps
somehow? I guess my biggest problem is summing with NULL values - maybe there
is a way to treat NULL values as 0? I'll have a look at the man page

Thanks,

Martin

-----Opprinnelig melding-----
Fra: Moritz Lennert [mailto:mlennert@club.worldonline.be]
Sendt: 14. april 2011 14:15
Til: Martin Album Ytre-Eide
Kopi: grass-user@lists.osgeo.org
Emne: Re: [GRASS-user] Raster addition

On 14/04/11 13:54, Martin Album Ytre-Eide wrote:
> Hello.
>
> I am trying to add some raster maps. I thought I could do this in
> r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where
> the maps overlap and ignoring areas where only on of the maps have
> values.

This is due to the way r.mapcalc handles NULL values. See the man page,
section NULL support for an explanation.

> I would like to do something similar to "v.overlay operator=or".
>
> Anyone who knows how to do this?

It depends on what you want the new map to contain as values. If you want
to add the value of old_1 to old_2 in places where they overlap, one way
would be to transform your null values to 0 using r.null null= and then
applying your formula.

If you just want a (any) value where one of the maps is non-null, then you
can use if. Something like this (untested):

new_map = if(!isnull(old_1) || !isnull(old_2), 1, null())

which should give you 1 where any of the two contains a value and a NULL
value elsewhere.

Moritz
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

--
GMX DSL Doppel-Flat ab 19,99 Euro/mtl.! Jetzt mit
gratis Handy-Flat! http://portal.gmx.net/de/go/dsl

6

Martin Album Ytre-Eide wrote:

I would like the NULL values that overlap with none NULL values to be
treated as 0, and still have NULL values where both maps have NULL values.
The combined map would be a large map with NULL values and added values.

hy,

i guess r.patch can do that for you ...
http://grass.osgeo.org/grass70/manuals/html70_user/r.patch.html r.patch ...
hope that i´m not wrong

cheers,
tim

--
View this message in context: http://osgeo-org.1803224.n2.nabble.com/Raster-addition-tp6272457p6272716.html
Sent from the Grass - Users mailing list archive at Nabble.com.

7

Don't know who of you led me in the right direction, but eventually the line:
"C=A + if(isnull(B),0,B)" in the manual solved my issue.

New_map = if(isnull(old_1),0,old_1) + if(isnull(old_2,0,old_2)) + etc and a following new_map=if(new_map>0,new_map,null())
I had four maps in my case, and that is why "new_map = if(!isnull(old_1) && !isnull(old_2), old_1+old_2,
if(!isnull(old_1) && isnull(old_2), old_1, etc)" would become to long (4!=24 statements?)

Thank you both Johannes and Moritz.

Martin

-----Opprinnelig melding-----
Fra: Johannes Radinger [mailto:JRadinger@gmx.at]
Sendt: 14. april 2011 15:13
Til: Martin Album Ytre-Eide; mlennert@club.worldonline.be
Kopi: grass-user@lists.osgeo.org
Emne: Re: SV: [GRASS-user] Raster addition

-------- Original-Nachricht --------

Datum: Thu, 14 Apr 2011 14:31:32 +0200
Von: Martin Album Ytre-Eide <Martin.Album.Ytre-Eide@nrpa.no>
An: \'Moritz Lennert\' <mlennert@club.worldonline.be>
CC: "grass-user@lists.osgeo.org" <grass-user@lists.osgeo.org>
Betreff: SV: [GRASS-user] Raster addition

I would like the NULL values that overlap with none NULL values to be
treated as 0, and still have NULL values where both maps have NULL
values. The combined map would be a large map with NULL values and added values.

that is possible with the r.mapcalc and a if condition like:

if(map A &&& map B, 0, null())

something like that (untested) might work. the null () provides NULL values where the condition is false. The triple &&& is the logic and (treats NULL values different from double &&).

see: http://grass.fbk.eu/gdp/html_grass64/r.mapcalc.html for more information.

/j

Maybe the best way is to use r.null and set NULL values to 0. Add the
maps and then convert the 0 values to NULL values?
Or could one set the value in the if statement to be a the sum of maps
somehow? I guess my biggest problem is summing with NULL values -
maybe there is a way to treat NULL values as 0? I'll have a look at
the man page

Thanks,

Martin

-----Opprinnelig melding-----
Fra: Moritz Lennert [mailto:mlennert@club.worldonline.be]
Sendt: 14. april 2011 14:15
Til: Martin Album Ytre-Eide
Kopi: grass-user@lists.osgeo.org
Emne: Re: [GRASS-user] Raster addition

On 14/04/11 13:54, Martin Album Ytre-Eide wrote:
> Hello.
>
> I am trying to add some raster maps. I thought I could do this in
> r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where
> the maps overlap and ignoring areas where only on of the maps have
> values.

This is due to the way r.mapcalc handles NULL values. See the man
page, section NULL support for an explanation.

> I would like to do something similar to "v.overlay operator=or".
>
> Anyone who knows how to do this?

It depends on what you want the new map to contain as values. If you
want to add the value of old_1 to old_2 in places where they overlap,
one way would be to transform your null values to 0 using r.null null=
and then applying your formula.

If you just want a (any) value where one of the maps is non-null, then
you can use if. Something like this (untested):

new_map = if(!isnull(old_1) || !isnull(old_2), 1, null())

which should give you 1 where any of the two contains a value and a
NULL value elsewhere.

Moritz
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

--
GMX DSL Doppel-Flat ab 19,99 Euro/mtl.! Jetzt mit gratis Handy-Flat! http://portal.gmx.net/de/go/dsl