[GRASS-user] Creating Raster Subsets in GRASS 7.0.0

[Jake Chila]

Hi Micha,

No worries, thanks for the headsup re: creating subsets. I noticed that
resolution thing also, and just thought that it was because that scene is
from a different path/row and the g.region command actually sets the region
on the edge of this scene, so there are null values from this scene in the
processing region. I have since gotten rid of this scene, but I figure that
might explain it?

JDC

On Tue, May 12, 2015 at 1:52 PM, Micha Silver <micha at arava.co.il> wrote:

>  Hi Jake
> Excuse for butting in...
>
> On 05/12/2015 05:23 PM, Jake Chila wrote:
>
> Hi Moritz,
>
> I definitely did mean 'g.region -p', sorry for that. I ended up getting it
> to work using 'r.mapcalc' after setting the region. I saw someone online
> had used it with the simple expression newmap=oldmap. Then, when I export
> the newmap it is only of the subset. This small workaround was easy to set
> up, but I don't have any idea why it didn't work in the first place.
>
>
> It's not a "workaround". The correct way to clip a section of a raster is
> two steps: define the new region with g.region, then run r.mapcalc (which
> honors the region settings) to get a new raster, at the new region
> settings, with values equal to the original.
>
> However, in your r.info output below, something seems wrong with the
> resolution. The landsat imagery is at 30 meters resolution. WHere did the
> (very small) values below come from? And why is the N-S 6 times smaller
> than the E-W ??
>
>
>
> r.info returns:
>
> (Tue May 12 11:19:01 2015)
>
> r.info map=L5_2007_ATCOR_COMP at Jacob
>
>
>  +----------------------------------------------------------------------------+
>  | Map:      L5_2007_ATCOR_COMP at Jacob       Date: Mon May 04 14:31:43
> 2015    |
>  | Mapset:   Jacob                          Login of Creator: Jacob
>     |
>  | Location: FordingRiver
>     |
>  | DataBase: C:\Users\Jacob\Documents\grassdata
>     |
>  | Title:     ( L5_2007_ATCOR_COMP )
>    |
>  | Timestamp: none
>    |
>
>  |----------------------------------------------------------------------------|
>  |
>    |
>  |   Type of Map:  raster               Number of Categories: 0
>     |
>  |   Data Type:    CELL
>     |
>  |   Rows:         11374
>    |
>  |   Columns:      12191
>    |
>  |   Total Cells:  138660434
>    |
>  |        Projection: UTM (zone 11)
>     |
>  |            N:     557000    S:     554300   Res: 0.23738351
>    |
>  |            E:     659000    W:     642200   Res: 1.37806579
>    |
>  |   Range of data:    min = 0  max = 32767
>     |
>  |
>    |
>  |   Data Description:
>    |
>  |    generated by r.composite
>    |
>  |
>    |
>  |   Comments:
>    |
>  |    r.composite red="GRASS_ATCOR_2007_B3 at Jacob"
> green="GRASS_ATCOR_2007_\   |
>  |    B2 at Jacob" blue="GRASS_ATCOR_2007_B1 at Jacob" levels=32
> output="L5_2007\   |
>  |    _ATCOR_COMP"
>    |
>  |
>    |
>
>  +----------------------------------------------------------------------------+
> (Tue May 12 11:19:02 2015) Command finished (0 sec)
>
>
> However, I have encountered a new problem. On one of my ETM+ images, the
> subset is returned as an empty raster. The process runs fine on the other
> ETM+ image from one year earlier but for some reason, the subset from the
> scene one year later has a min and max data range of 'NULL'. This range
> appears to be constant across all the other scenes, so is there a way for
> me to quickly edit this scene so it has the correct data?
>
>
> As before, I would double check "g.region -p", and "r.info" for both the
> original Landsat image, and the clipped image that comes out NULL.
>
>
>  Thanks,
>
> JDC
>
> On Tue, May 12, 2015 at 3:33 AM, Moritz Lennert <
> mlennert at club.worldonline.be> wrote:
>
>> On 08/05/15 19:13, Jake Chila wrote:
>>
>>> Hey all,
>>>
>>> I am currently working with some landsat data in Grass 7.0.0 on windows
>>> 7, and am trying to hone in on my study area (much smaller than the
>>> whole scene). From what I can tell, the best way to do this is through
>>> the 'g.region' command however, I am having significant problems getting
>>> this module to run correctly.
>>>
>>> my input is:
>>>
>>> g.region n=5572425 s=5536865 e=655050 w=626350 res=30
>>>
>>> One thing is that it runs in '0 seconds' so I think that is a little odd.
>>>
>>
>>  It's normal as the command just changes a few entries in a text file, so
>> it is really fast.
>>
>>
>>> When I use the 'g.region -d' command I can see that everything is set
>>> properly,
>>>
>>
>>  Did you maybe mean g.region -p ? At least this is the command you should
>> use to check current region settings.
>>
>>  however when I update the map display nothing changes. Also,
>>> when I export the file using 'r.out.gdal' it exports nothing.
>>>
>>>
>>> ('r.out.gdal -t -f --overwrite input=LT5_2007_ATCORRCOMP at May_Project
>>> output=C:\Users\Jacob\Desktop\GRASS_Trials\exportattempt5 format=GTiff
>>> type=Uint16 nodata=0)
>>>
>>
>>  That should normally respect the region settings.
>>
>> What does
>>
>> r.info LT5_2007_ATCORRCOMP
>>
>> give you ?
>>
>> Moritz
>>
>
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