[GRASS-user] Re: r.fillnulls for large area

[Nick Jachowski]

Dear All,

Thanks for all the help on this matter. Sorry for the late reply (fieldwork
and vacation got in the way...)!

I ended up solving the problem by (1) filling the ocean nulls, (2)
splitting the region into subregions, and (3) running it on a more powerful
machine.

Best,
Nick

On Fri, Dec 2, 2011 at 11:39 PM, pkscwc <pkscwc at gmail.com> wrote:

> Dear Nick,
>
> I am working on SRTM rasters of resolution 1km, 500m, 250m and recently 90m
> using GRASS for long and had countered the problem being faced by you.
>
> My workaround is given below and as a by-product you may get a very nice
> coastline vector/raster also.
>
> 1. I have converted  all the nulls with r.mapcalc to -160 using the formula
> C=if(A, if(isnull(B),-160,B))
> Where,
> A: region of interest
> B: original srtm raster with nulls for sea and holes
> C: Output map in which nulls have been converted to -160.
>
> (Why -160, because in my map, as from my human memory, the lowest value was
> -70. I just chose a value lower than this value. We will need it later on
> to
> convert back them as holes for r.fillnulls to work upon.)
>
> A sample from the history file of the raster is produced below:
>
> Sun Aug  1 17:49:10 2010
> test5
> PERMANENT
> pks
> raster
>
>
> generated by r.mapcalc
> if(test_nL_region at PERMANENT, if(isnull(ib2 at PERMANENT), -160, ib2 at PERMANENT
> ))
>
>
> A: test_nL_region
>
> This raster map is a region of my interest out the big srtm raster
> converted
> from a vector. Grass has a command , which converts the current region to a
> vector file.
> Again, the sample from the history file of the raster is produced below:
>
> ed Jul 28 10:09:42 2010
> test_nL_region
> PERMANENT
> pks
> raster
> Vector Map: nL_region at PERMANENT in mapset PERMANENT
> Original scale from vector map: 1:1
> generated by v.to.rast
> v.to.rast input="nL_region at PERMANENT" output="test_nL_region" use="c\
> at" type="point,line,area" layer=1 value=1 rows=4096
>
> nL_region:
> Again, the sample from the history file of the vector is produced below:
> COMMAND: v.in.region output="nL_region" type="area" cat=1
> GISDBASE: /home/pks/renamed_grassdata
> LOCATION: newLocation MAPSET: PERMANENT USER: pks DATE: Wed Jul 28 09:53:43
> 2010
>
> So, now we have -160s all around , i.e. the sea and holes on land.
>
> Now use the r.reclass.area feature to differentiate sea from  holes on
> land.
> A sample from my recent work is given below:
>
> Tue Nov  8 13:55:47 2011
> bi_reclassed3_area.recl
> work2
> rdcgis1
> reclass
> Reclassified map based on:
>  Map [bi_reclassed3.clump.bi_reclassed3_area] in mapset [work2]
> generated by r.reclass
>
> I am using GRASS7 and in the history given above , all the parameters are
> not available.
> In my case , I used 1 billion hectare as "greater than area" parameter to
> bring out the sea , land , and holes in land in different categories.
>
> Thereafter, use mask and pick up the landmass with holes in land , which
> you
> want to fill.
> Just remember to convert back the -160 to null again.
>
> I felt that r.fillnulls works best when the nulls have values around them.
>
> By the way, CGIAR provides holes-filled-SRTM-raster.You may like to read
> their literature for understanding the algorithms used to fill the nulls.
> It's good and useful.
>
> Try this link for downloading clean rasters of your area of interest:
>
> http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp
>
> Hope, it helps.
>
> Some of my observations are listed below:
> 1. If the system lacks RAM, then  increase patience.
> 2. If the system lacks hard-disk space, don't go for GIS.
> 3. Learn python.
>
> --
> View this message in context:
> http://osgeo-org.1803224.n2.nabble.com/r-fillnulls-for-large-area-tp7047337p7057352.html
> Sent from the Grass - Users mailing list archive at Nabble.com.
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>
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