[GRASS-stats] gstat error

[Edzer Pebesma]

Jarek has sent me the data off-line, and it turns out that the data are
three-dimensional, but lack variability in the third dimension:

> summary(p)
Object of class SpatialPointsDataFrame
Coordinates:
              min     max
coords.x1 3560158 3575935
coords.x2 5636873 5653748
coords.x3       0       0
Is projected: TRUE
proj4string :
[+proj=stere +lat_0=51.67083333333333 +lon_0=16.67222222222222
+k=0.999800 +x_0=3703000 +y_0=5627000 +no_defs +a=6378245 +rf=298.3
+towgs84=33.4,-146.6,-76.3,-0.359,-0.053,0.844,-0.84 +to_meter=1]
Number of points: 200
Data attributes:
...

Using the "degree=1" way of trend analysis, a first order linear trend
is computed in the coordinates, meaning in z as well, and this is the
cause of failure. Ignoring z, one can e.g. do

p$x=coordinates(p)[,1]
p$y=coordinates(p)[,2]
r$x=coordinates(r)[,1]
r$y=coordinates(r)[,2]
pg=gstat(id="p_1", formula=rzedna~x+y,data=p)
p_1=predict(pg,r)
spplot(p_1)

of course, no standardization of coordinates takes place here, so this
approach will fail for high order trends.
--
Edzer

Jarek Jasiewicz wrote:
>
>
> Edzer Pebesma pisze:
>> Jarek Jasiewicz wrote:
>>  
>>> Hi
>>> during trend calculation I recive following error:
>>>
>>> R
>>> library(spgrass6)
>>> library(gstat)
>>>
>>> raster=readRAST6("rzedna")
>>> p=readVECT6("punkty")
>>> p at proj4string=raster at proj4string
>>>
>>> pg_1=gstat(id="p_1", formula=rzedna~1,data=p, degree=1)
>>> p_1=predict(pg_1,raster)
>>> [ordinary or weighted least squares prediction]
>>>
>>> "solve.c", line 87: singular matrix in function Usolve()
>>> Error in predict.gstat(pg_1, raster) : Usolve
>>>     
>> There are several situations why this can happen that are hard to
>> distinguish from the point where the error happens. The most likely in
>> your case (first order trend surface estimation) is that your data are,
>> geographically, on a line, i.e. one-dimensionally. Or similary, that you
>> have less than 3 observations. Is that the case?
>> -- 
>> Edzer
>>   
>
> Thanks for answer,  but none of that case. Tt is regular data file
> with 200 random observations generated with v.random in GRASS and
> stored as SpatialPointDataFrame.
> before I  posted to the list  I had tried to reproduce it on my
> archive data with archive scripts (which worked  in older R
> compilation) and it ALWAYS fail (on every data I tested).
>
> In general, the possible problem on my side coud be that I
> (experientally) installed R from CRAN ubuntu repository instead to
> compile from source. The ubuntu CRAN-R packages do not include lapack.
> This is the only difference I noticed.
>
> If you need I can send you sample R file (is small, no more than 2MB)
>
> Jarek
>
>>> my system information:
>>>
>>> Ubuntu 8.04
>>> R 2.8.1
>>> gstat 0.9.59
>>> the error have appeared first time on gstat 0.9.49
>>>
>>> Errors apears on all my data, even these, where trend was calculated
>>> some times ago. Commads coming from old data
>>>
>>> The error is also reproducible on spearfish dataset with elevation.dem
>>> and random points generated by v.random
>>>
>>> Jarek
>>> _______________________________________________
>>> grass-stats mailing list
>>> grass-stats at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/grass-stats
>>>     
>>
>>   
> _______________________________________________
> grass-stats mailing list
> grass-stats at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-stats

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/
http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de