Re: [GRASS-user] v.rast.stats with mode?

[Moritz Lennert]

On 31/03/16 10:32, patrick s. wrote:

Following Anna's suggestion I had to find out that r.mode has to option
to handle NULL values, i.e. exclude it from calculation? I need to
aggregate rasters to polygons, with rasters covering only a small part
of the polygon. As I realized now r.mode returns NULL in such case.



I cannot reproduce this issue with grass7. Try the following in the NC 
demo dataset:


g.region vector=census_wake2000@PERMANENT res=500 -a
v.random -a output=points npoints=5 restrict=census_wake2000@PERMANENT 
column_type=integer --o

v.kcv map=points@user1 npartitions=3
v.to.rast input=census_wake2000@PERMANENT output=census use=attr 
attribute_column=ID --o
v.to.rast input=points@user1 output=points use=attr 
attribute_column=part --o

r.mode base=census@user1 cover=points@user1 output=census_points_rmode --o

The results seem correct: even though there are just 5 points in each 
census area, and most pixels are thus NULL in the points map, the mode 
corresponds to 1, 2 or 3.


> Setting NULL with r.null null= it will return  for all of these.

If you have more NULL cells than others, and you replace the NULL value 
by an integer value, you will obviously get that value as mode...


Moritz
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Re: [GRASS-user] v.rast.stats with mode?

[Anna Petrášová]

On Thu, Mar 31, 2016 at 4:32 AM, patrick s.  wrote:
> Following Anna's suggestion I had to find out that r.mode has to option to
> handle NULL values, i.e. exclude it from calculation? I need to aggregate
> rasters to polygons, with rasters covering only a small part of the polygon.
> As I realized now r.mode returns NULL in such case. Setting NULL with r.null
> null= it will return  for all of these.
>
> Is there a solution to that problem?

I am not sure I understand, is this related to this?
https://lists.osgeo.org/pipermail/grass-dev/2015-October/076654.html

Could you provide more details?

Thanks
Anna

> Patrick
>
>
>
>
> On 16.03.2016 13:59, Anna Petrášová wrote:
>
>
>
> On Wed, Mar 16, 2016 at 6:23 AM, patrick s.  wrote:
>>
>> Dear list
>>
>> Is it possible to get the "mode" (most common occurring value) in a
>> polygon for discrete classes? It appears that v.rast.stats does not have
>> this option.
>
>
> v.rast.stats uses r.univar and r.univar doesn't have mode implemented (it's
> a TODO in manual). You can look at r.mode but it returns raster map, not one
> number.
>
> Anna
>
>>
>> Thanks for a short feedback,
>> Patrick
>>
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>
>
>
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Re: [GRASS-user] v.rast.stats with mode?

[patrick s.]

Following Anna's suggestion I had to find out that r.mode has to option 
to handle NULL values, i.e. exclude it from calculation? I need to 
aggregate rasters to polygons, with rasters covering only a small part 
of the polygon. As I realized now r.mode returns NULL in such case. 
Setting NULL with r.null null= it will return  for all of these.


Is there a solution to that problem?
Patrick




On 16.03.2016 13:59, Anna Petrášová wrote:



On Wed, Mar 16, 2016 at 6:23 AM, patrick s. > wrote:


Dear list

Is it possible to get the "mode" (most common occurring value) in
a polygon for discrete classes? It appears that v.rast.stats does
not have this option.


v.rast.stats uses r.univar and r.univar doesn't have mode implemented 
(it's a TODO in manual). You can look at r.mode but it returns raster 
map, not one number.


Anna


Thanks for a short feedback,
Patrick

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Re: [GRASS-user] v.rast.stats with mode?

[Anna Petrášová]

On Wed, Mar 16, 2016 at 6:23 AM, patrick s.  wrote:

> Dear list
>
> Is it possible to get the "mode" (most common occurring value) in a
> polygon for discrete classes? It appears that v.rast.stats does not have
> this option.
>

v.rast.stats uses r.univar and r.univar doesn't have mode implemented (it's
a TODO in manual). You can look at r.mode but it returns raster map, not
one number.

Anna


> Thanks for a short feedback,
> Patrick
>
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Re: [GRASS-user] v.rast.stats with mode?

[patrick s.]

Thanks, Anna. That helps!

Cheers, Patrick



On 16.03.2016 13:59, Anna Petrášová wrote:



On Wed, Mar 16, 2016 at 6:23 AM, patrick s. > wrote:


Dear list

Is it possible to get the "mode" (most common occurring value) in
a polygon for discrete classes? It appears that v.rast.stats does
not have this option.


v.rast.stats uses r.univar and r.univar doesn't have mode implemented 
(it's a TODO in manual). You can look at r.mode but it returns raster 
map, not one number.


Anna


Thanks for a short feedback,
Patrick

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[GRASS-user] v.rast.stats with mode?

[patrick s.]

Dear list

Is it possible to get the "mode" (most common occurring value) in a 
polygon for discrete classes? It appears that v.rast.stats does not have 
this option.


Thanks for a short feedback,
Patrick

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