[R-sig-Geo] [SoC v.autokrige2.py] autoKrige() and projected data

[Anne Ghisla]

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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
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