[R-sig-Geo] write.asciigrid

[Roger Bivand]

On Tue, 9 May 2006, Zev Ross wrote:

> Hi Roger and Andy,
> 
> Thanks for the help. I'm using ArcGIS 9.1. writeGDAL works as promised.
> The one odd behavior was the initial display in ArcGIS once I first added
> the two bands. Using the "stretched" classification, the map initially
> looked all black. Under properties, I changed the symbology to
> "Classified" and it looked fine -- then I changed back to "Stretched" and
> again it looked fine. Quirky behavior like this from ArcGIS is nothing
> new.

Did you do the:

ArcToolbox | Data Management Tools | Raster | Calculate Statistics

trick too? I think that is what Arc (sometimes) does on the fly when 
changing symbology (dreadful term!). But when NAs are present, it can get 
stuck.

> 
> I tried the suggested write ascii command from maptools on my own data
> set and it didn't work initially due to the fact that my grid cells
> apparently are not perfect squares (perhaps this is a rounding issue). No
> need to keep fiddling with that, though, as writeGDAL does the trick.
> Thanks again,
> 

Yes, they need to be equal for the Arc ASCII grid route to work. If they 
are, it works (when the decimal point in FLOAT is correct too).

Roger

> Zev
> 
> Roger Bivand wrote:
> 
>  On Thu, 4 May 2006, Zev Ross wrote:
> 
>   
> 
>  Hi All,
> 
> I'd like to write the results of a kriging call to an ascii grid using
> GSTAT -- but I would like to write BOTH the predictions and the variances
> to grids. Is there a more elegant (and less dangerous) way to do it than
> what I have below?
> 
>     
> 
>  Dangerous for whom? Elegant, would be nice but life is short? The answer 
> depends on the software that is going to read the output grids, and how it 
> treats locales, etc., since both predictions and variances will be 
> floating point.
> 
>   
> 
>  depth_uk <- krige(DEPTH~slope.asc, depth, slope, vgm_depth_r)
> 
> #  write the predictions
> 
> write.asciigrid(depth_uk "c:/junk/rk/predictions.asc")
> 
> # replace predictions with variances and then write the variances
> 
> depth_uk$var1.pred<-depth_uk$var1.var
> write.asciigrid(depth_uk, "c:/junk/rk/.asc")
> 
>     
> 
>  If the software on the other side reads GeoTiff, my preference would be:
> 
> library(rgdal)
> writeGDAL(depth_uk, "depth_uk.tif")
> 
> which I have seen work with ENVI, but not with ArcGIS 9.1; this preserves 
> coordinate reference system metadata if set.
> 
> In a forthcoming release of rgdal, you should be able to pass options= to 
> writeGDAL() - specifically INTERLEAVE=PIXEL, see:
> 
> http://grass.itc.it/grass61/manuals/html61_user/r.out.gdal.html
> 
> and I have seen this help with ArcGIS 9.1, although it wasn't predictable
> (the legend scale showed correct values but the visualisation was wrong
> sometimes - I tried on a Wednesday if that helps!). ArcGIS only accepted 
> single band GeoTiff files, it thought 3-band were coloured images. ENVI 
> simply read the GDAL-generated GeoTiffs (with 4 bands in the case we 
> tried - point pattern kernel densities at different bandwidths) correctly 
> without making any assumptions.
> 
> Depending on your locales, the ASCII grid route is being maintained in the 
> maptools package and functions in the sp package will be deprecated. So
> 
> library(maptools)
> writeAsciiGrid(depth_uk, "preds.txt", attr="var1.pred", dec=<your choice>)
> writeAsciiGrid(depth_uk, "vars.txt", attr="var1.var", dec=<your choice>)
> 
> should get the values into ArcGIS 9.1 through the Toolbox (it is very 
> sensitive to the "."/"," dec= setting). [The intention is to gather 
> input/output functions in maptools and rgdal, freeing the other packages 
> from having often older, duplicate copies of functions that do not get 
> maintained.]
> 
> Again, how to do it does depend on what software is going to read the 
> output ASCII grids, and what assumptions (often undocumented) it makes 
> about the files.
> 
> Please let us know how you get on,
> 
> Roger
> 
>   
> 
>  PS this sample code comes from Tomislav Hengl's page
> (http://spatial-analyst.net/regkriging.php)
> 
>     
> 
>  Nice link!
> 
>   
> 
>  Zev
> --
> Zev Ross
> ZevRoss Spatial Analysis
> 303 Fairmount Ave
> Ithaca, NY 14850
> (607) 277-0004 (phone)
> (866) 877-3690 (fax toll-free)
> zev at zevross.com
> www.zevross.com
> 
> 
>     
> 
> 
> --
> Zev Ross
> ZevRoss Spatial Analysis
> 303 Fairmount Ave
> Ithaca, NY 14850
> (607) 277-0004 (phone)
> (866) 877-3690 (fax toll-free)
> zev at zevross.com
> www.zevross.com
> 
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no