[GRASS-user] create a mask to exclude plate area

GRASS GRASS user
1

Bonjour
Je travaille actuellement sur des problématiques liées à la viticulture
de montagne, qui répond a des critères bien précis (altitude supérieure
a 500, ou pente supérieure a 30%)à partir des données DRTM. J’ai donc
créé un masque qui permette de délimiter ces zones.
Maintenant je dois exclure les zones de plateau (par exemple les
plateaux espagnols) mais je n'arrive pas à visualiser quel critère
utiliser pour cela.
J’ai pensé faire une commande r.mapcalc avec une requête à la fois sur
la superficie, et sur la pente. Est-ce que vous pourriez m'aider à créer
ce masque?

Merci

Hello
I am currently working on issues related to mountain viticulture, which
responds to specific criteria (above a 500, or upper slope 30%) from
data SRTM. So I created a mask that allows to define these areas.
Now I have to exclude the plate areas (eg trays Spanish) but I can not
see any use for this test.
I thought r.mapcalc place an order with a request to both area and on
slope. Can you help me to create this mask, or give me an idea?
thank you

--
Cordialement

Etienne DELAY
Deust "Webmaster et gest. d'intranet" (IDSkype : etienne.delay.tic)
Master IUP "valorisation du patrimoine et aménagement du territoire"

2

Etienne DELAY wrote:

Bonjour

Bonjour Monsieur, mon francais est terrible :-O. Si’ll vous plait regardez ci-apres (en anglais).

Je travaille actuellement sur des problématiques liées à la viticulture

de montagne, qui répond a des critères bien précis (altitude supérieure

a 500, ou pente supérieure a 30%)à partir des données DRTM. J’ai donc

créé un masque qui permette de délimiter ces zones.

Maintenant je dois exclure les zones de plateau (par exemple les

plateaux espagnols) mais je n’arrive pas à visualiser quel critère

utiliser pour cela.

J’ai pensé faire une commande r.mapcalc avec une requête à la fois sur

la superficie, et sur la pente. Est-ce que vous pourriez m’aider à créer

ce masque?

Merci

Hello

I am currently working on issues related to mountain viticulture, which

responds to specific criteria (above a 500, or upper slope 30%) from

data SRTM. So I created a mask that allows to define these areas.

How? Which command(s) exactly? Using r.mapcalc? There is also r.mask [1]

Also, tres-important, did you define the “region” of your interest using “g.region”[2]?

Now I have to exclude the plate areas (eg trays Spanish) but I can not

see any use for this test.

I thought r.mapcalc place an order with a request to both area and on

slope.

That is right. r.mapcalc (or most of the raster modules) will ignore the MASKed-out cells by the raster map named MASK.

Radom example grepped from the grass-user list:

–%<— Re: How To use a raster MASK correctly? --17/10/2009 20:09 --%<—

Figured it out. Used the following r.mapcalc expression:

r.mapcalc “new_hillshade=if(europe_dem < 100, 180, europe_hillshade)”

–>%—

Cordialement, Nikos

[1] http://grass.osgeo.org/grass65/manuals/html65_user/r.mask.html

[2] http://grass.osgeo.org/grass65/manuals/html65_user/g.region.html

3

How? Which command(s) exactly? Using r.mapcalc? There is also r.mask [1]
Also, tres-important, did you define the "region" of your interest using
"g.region"[2]?

Now I have to exclude the plate areas (eg trays Spanish) but I can not
see any use for this test.
I thought r.mapcalc place an order with a request to both area and on
slope.

That is right. r.mapcalc (or most of the raster modules) will ignore the
MASKed-out cells by the raster map named MASK.

Radom example grepped from the grass-user list:

--%<--- Re: How To use a raster MASK correctly? --17/10/2009 20:09 --%<---
Figured it out. Used the following r.mapcalc expression:
r.mapcalc "new_hillshade=if(europe_dem < 100, 180, europe_hillshade)"
-->%---

Cordialement, Nikos

---
[1] <http://grass.osgeo.org/grass65/manuals/html65_user/r.mask.html&gt;
[2] <http://grass.osgeo.org/grass65/manuals/html65_user/g.region.html&gt;

Hello Nikos
sorry for the French, I need to think in my language :slight_smile:
So I have no problem using r.mapcalc for 1st and 2nd criteria, and to
assemble the two masks. The region is also parameterize, but now, it has
become a 3rd test, I must arrive in isolating the flat portions of the
mountain in Spain, if not that is reflected in part authorize my mask,
but not know structural problems in they vineyards ...

I want to use something like:

r.mapcalc "Maskplate= if((Area>100000ha && slope<=10%), 1, null())

mais l'utilisation de aire ne me satisfait pas vraiment.... parce quelle
peut changer en longueur et largeur...

but the use of area does not really satisfy me .... because what can
change in length and width ...

Is there a solution would be to make visual grade, to define the
geomorphological unite?

thank you very much :wink:

--
Cordialement

Etienne DELAY
Deust "Webmaster et gest. d'intranet" (IDSkype : etienne.delay.tic)
Master IUP "valorisation du patrimoine et aménagement du territoire"

4

Bonsoir Étienne,
Je crois comprendre que ton problème se rapporte à l'identification de
zones sur des critères géomorphologiques. Peut-être pourrais-tu partir
sur un traitement avec r.mapcalc ou des outils comme r.reclass pour
"lisser" ta topo ou du moins discrétiser ta carte des pentes, afin
d'identifier des zones homogènes. Puis transformer ces zones en
polygones (r.to.vect) et faire des ratios entre périmètre et
superficie...

I guess your problem is related to a geomorphological identification
process. I suggest you to try and make a kind of slopes reclassification
in order to discretize and aggregate homogenous slope areas, then turn
these areas into a polygon vector map. After that you can compute ratios
between perimeters, areas, X/Y extension, and so on...

Amuse-toi bien

Enjoy it !

Vincent.

Le lundi 19 juillet 2010 à 21:39 +0200, Etienne DELAY (deust 2010) a
écrit :

> How? Which command(s) exactly? Using r.mapcalc? There is also r.mask [1]
> Also, tres-important, did you define the "region" of your interest using
> "g.region"[2]?
>
>> Now I have to exclude the plate areas (eg trays Spanish) but I can not
>> see any use for this test.
>> I thought r.mapcalc place an order with a request to both area and on
>> slope.
>
> That is right. r.mapcalc (or most of the raster modules) will ignore the
> MASKed-out cells by the raster map named MASK.
>
> Radom example grepped from the grass-user list:
>
> --%<--- Re: How To use a raster MASK correctly? --17/10/2009 20:09 --%<---
> Figured it out. Used the following r.mapcalc expression:
> r.mapcalc "new_hillshade=if(europe_dem < 100, 180, europe_hillshade)"
> -->%---
>
> Cordialement, Nikos
>
> ---
> [1] <http://grass.osgeo.org/grass65/manuals/html65_user/r.mask.html&gt;
> [2] <http://grass.osgeo.org/grass65/manuals/html65_user/g.region.html&gt;
>

Hello Nikos
sorry for the French, I need to think in my language :slight_smile:
So I have no problem using r.mapcalc for 1st and 2nd criteria, and to
assemble the two masks. The region is also parameterize, but now, it has
become a 3rd test, I must arrive in isolating the flat portions of the
mountain in Spain, if not that is reflected in part authorize my mask,
but not know structural problems in they vineyards ...

I want to use something like:

r.mapcalc "Maskplate= if((Area>100000ha && slope<=10%), 1, null())

mais l'utilisation de aire ne me satisfait pas vraiment.... parce quelle
peut changer en longueur et largeur...

but the use of area does not really satisfy me .... because what can
change in length and width ...

Is there a solution would be to make visual grade, to define the
geomorphological unite?

thank you very much :wink:

5

Le 19/07/10 22:25, Vincent Bain a écrit :

Bonsoir Étienne,
Je crois comprendre que ton problème se rapporte à l'identification de
zones sur des critères géomorphologiques. Peut-être pourrais-tu partir
sur un traitement avec r.mapcalc ou des outils comme r.reclass pour
"lisser" ta topo ou du moins discrétiser ta carte des pentes, afin
d'identifier des zones homogènes. Puis transformer ces zones en
polygones (r.to.vect) et faire des ratios entre périmètre et
superficie...

I guess your problem is related to a geomorphological identification
process. I suggest you to try and make a kind of slopes reclassification
in order to discretize and aggregate homogenous slope areas, then turn
these areas into a polygon vector map. After that you can compute ratios
between perimeters, areas, X/Y extension, and so on...

Amuse-toi bien

Enjoy it !

Vincent.

Hello Vincent
first thank you for putting the good word on my request (though I
searched long), and thank you for french :-). In fact my brain is broke
down, si can you, or others give me an example with r.mapcalc or
r.reclass, for this request?
thank you :wink:

Bonjour Vincent
en premier merci d'avoir mis les bons mots sur ma demande (j'ai pourtant
cherché longtemps). En fait, mon cerveau fait un blocage. Est-ce que
toi ou un autre pourriez me donner un exemple avec r.mapcalc, ou r.reclass?
Parce que je ne vois pas comment fonctionne ce type de requête.
merci :wink:

--
Cordialement

Etienne DELAY
Deust "Webmaster et gest. d'intranet" (IDSkype : etienne.delay.tic)
Master IUP "valorisation du patrimoine et aménagement du territoire"

6

Etienne,

if the main difficulty is about how to combine two criteria in one "r.mapcalc"
command, then, I recommend to go through the r.mapcalc manual [1]. There are
many examples. Also read the old (but very good) tutorial [2] (which is
referenced in the manual).

Nikos

---
[1] <http://grass.osgeo.org/grass64/manuals/html64_user/r.mapcalc.html&gt;
[2] <http://grass.osgeo.org/gdp/raster/mapcalc-algebra.pdf&gt;