[SoC v.autokrige2.py] autoKrige() and projected data
If newdata is created automatically (and this makes sense), it should recieve the projection information of data. On another issue: what happens if both are provided but have different projection attributes? And what happens if data has long/lat coordinates (is.projected(data) == FALSE)? In that case I would prefer an error -- the current interpolation methods (covariances) used are not appropriate. Best regards, -- Edzer
Anne Ghisla wrote:
Hello Paul, Edzer, the integration of automap package in v.autokrige2 is quite completed [0], thanks Paul for this clean interface to gstat! Sadly, I'm getting an error when autoKrige() receives no new_data argument. Examples in documentation all involve meuse dataset, that has no projection information. I browsed the Web for this situation with little success. I don't know precisely where the error occurs, so I send this report to Edzer too. Here is the code and a traceback of the error: ---code--- require(spgrass6) require(automap) # rs in a vector map containing locations with relative elevation value, in GRASS spearfish60 dataset. Obtained following this tutorial [1]
rsmap <- readVECT6('rs', type='point')
Exporting 300 points/lines... 100% 300 features written OGR data source with driver: ESRI Shapefile Source: "/home/anne/gis/spearfish60/PERMANENT/.tmp/galadriel", layer: "rs" with 300 rows and 2 columns Feature type: wkbPoint with 2 dimensions
str(rsmap)
Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots [cut] ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots .. .. ..@ projargs: chr " +proj=utm +zone=13 +ellps=clrk66 +datum=NAD27 +units=m +no_defs +nadgrids=@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat" # not shown: meuse object has the same structure and contents but projargs==NA.
autoKrige(elev~1, rsmap)
Errore in predict.gstat(g, newdata = newdata, block = block, nsim =
nsim, :
var1 : data item in gstat object and newdata have different coordinate
reference systems
Then I had a look into autoKrige code and found these lines:
if (missing(new_data))
new_data = create_new_data(input_data)
krige_result = krige(formula, input_data, new_data,
variogram_object$var_model,
block = block, ...)
My guess is that create_new_data() creates non-projected grid, and
krige() calls predict.gstat() with input_ and new_data, checks if they
have the same projection and in this case fails.
In v.autokrige.py code, Mathieu Grelier workarounded this autogeneration
of new_data creating a correctly projected grid and passing it as
parameter.
Shall I do the same or is it possible to get create_new_data() to keep
input_data's projection?
many thanks in advance,
Anne
[0] http://grass.osgeo.org/wiki/V.autokrige_GSoC_2009
[1] http://casoilresource.lawr.ucdavis.edu/drupal/node/438
Edzer Pebesma Institute for Geoinformatics (ifgi), University of M?nster Weseler Stra?e 253, 48151 M?nster, 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