[GRASS-user] Re: Help - Output difference between ARCGIS enviroment settings and GRASS g.region function

[Markus Metz]

On Tue, May 8, 2012 at 9:41 PM, Alejandro Coca Castro <acocac at gmail.com> wrote:
> Hi Mark, i followed your instructions, so i put in command-line
>
This
> g.region rast=MASK at default nsres=0:00:07.5 ewres=0:00:07.5

will adjust, i.e. modify the resolution in order to fit into the
extents. The extents are not modified. In GRASS, the extents have
precedence over resolution, unless you use the -a flag, in which case
the extents are aligned to the desired resolution. Thus use either

g.region rast=MASK at default nsres=0:00:07.5 ewres=0:00:07.5 -a

to align the current region to the desired resolution and enforcing
this resolution, or

g.region rast=MASK at default

You can check if the current region is all right with g.region -p or
g.region -g, before doing any processing.

I tried to set the region with the gdalinfo output of the ArcMap
raster fileASC_ARCMAP.asc:

g.region w=-60.9250001 e=-49.9979167 n=-0.0000001 s=-10.0000001
res=0.00208333333

Output of g.region -g:
n=-1e-07
s=-10.0000001
w=-60.9250001
e=-49.9979167
nsres=0.00208333333333333
ewres=0.00208333334604385
rows=4800
cols=5245
cells=25176000

As you can see, the resolution needed to be adjusted, i.e. there are
floating point rounding errors in fileASC_ARCMAP.asc. Using rounded
DD:MM:SS.S format:

g.region w=60:55:30W e=49:59:52.5W n=0 s=10S res=00:00:07.5

Output of g.region -g:
n=0
s=-10
w=-60.925
e=-49.9979166666667
nsres=0.00208333333333333
ewres=0.00208333333333333
rows=4800
cols=5245
cells=25176000

This is probably the desired extents and resolution, the resolution
did not need to be adjusted (0.00208333333333333 = 00:00:07.5) .

Markus M

>
> Now, I get the same number of columns and rows. However, the cell size isn't
> the same that ArcMAP output file...so i think it can be the reason of
> non-similar extend and origin....
>
> Below i show you the output gdalinfo,
>
> Driver: AAIGrid/Arc/Info ASCII Grid
> Files: D:\gras_data\temp\test5.asc
>
> Size is 5245, 4800
> Coordinate System is `'
> Origin = (-60.924999999999997,-0.001600000000000)
> Pixel Size = (0.002083000000000,-0.002083000000000)
> Corner Coordinates:
> Upper Left  ( -60.9250000,  -0.0016000)
> Lower Left  ( -60.9250000, -10.0000000)
> Upper Right ( -49.9996650,  -0.0016000)
> Lower Right ( -49.9996650, -10.0000000)
> Center      ( -55.4623325,  -5.0008000)
> Band 1 Block=5245x1 Type=Int32, ColorInterp=Undefined
>   NoData Value=-9999
>
> Do you have others ideas?
> ------
>
> Jacquie, thanks for your comments, i hope the next SPs versions fix these
> kind of bugs.
>
> regards,
>
> 2012/5/8 Alejandro Coca Castro <acocac at gmail.com>
>>
>> Hi, i tried to convert the following enviroments settings to GRASS
>> g.region and r.mask for the next ARCGIS output (ASCII file):
>>
>>     fileTIF = r"x:\test\fileTIF.tif"
>>     MASK = r"x:\test\mask_file"
>>     env.extent = fileTIF
>>     env.snapRaster = MASK
>>     env.mask = MASK
>>     fileGRD = r"x:\test\fileGRD"
>>     outCon = Con(fileTIF, fileTIF, "", "VALUE >= 0")
>>     outCon.save(fileGRD)
>>     fileASC = r"x:\test\fileASC.asc"
>>     env.workspace = fileGRD
>>     RasterToASCII_conversion(fileGRD,fileASC)
>>
>> So, i put on the GRASS command-line:
>>
>> r.mask input=mask_file at default
>> g.region rast=fileTIF at default res=0.00208333333 align=MASK at default
>> r.mapcalc fileGRD = if(fileTIF at default  < 0 , null(), fileTIF at default)
>> r.out.arc input= fileGRD at default output=x:\test\fileASC_grass.asc
>>
>> However, the ArcGIS and GRASS outputs had a different extend and curiously
>> the GRASS output didn't snap their cells with the MASK. Also, when i observe
>> the GRASS output cellsize, it only has the first 6 decimals (f.e.
>> 0.002083)....
>>
>> Finally i tried to setup the parameters of g.region with the ArcGIS output
>> but GRASS output definetly didnt have the same properties of ArcGIS output
>> (cellsize, columns and rows, extend)
>>
>> If somebody knows how can i fix it, i'll be grateful,
>>
>> Thanks in advance,
>>
>> Alejandro
>
>
>
>
> --
> Alejandro Coca Castro