rgrass7 and snow

Le vendredi 22 avril 2016, Dr Didier G. Leibovici 
<didier.leibovici at nottingham.ac.uk 
<mailto:didier.leibovici at nottingham.ac.uk>> a ?crit :

    Hi,

    we are trying to use 'grass' in parallel programming with 'snow'

    The code does multiple simulations of a r.viewshed resampling the
    points
    generating the viewshed.
    (I guess the other solution would be to have an equivalent of
    r.viewshed
    in an R library or script) ...
    I think the problems are to do with the gisDbase ...

    Testing with 2 clusters we start with:

     >  clusterCall(cl,initGRASS,"/usr/lib/grass70",home=getwd(),

    gisDbase="GRASS_TEMP", override=TRUE )
    [[1]]
    gisdbase    GRASS_TEMP
    location    file5edb6bf06d70
    mapset      file5edb4b0cda81
    rows        1
    columns     1
    north       1
    south       0
    west        0
    east        1
    nsres       1
    ewres       1
    projection  NA

    [[2]]
    gisdbase    GRASS_TEMP
    location    file5edb6bf06d70
    mapset      file5edb4b0cda81

    then read a DEM
    clusterCall(cl,execGRASS,"r.in.gdal", flags="o",
    parameters=list(input=baseDemFilename, output="DEM"))
       clusterCall(cl,execGRASS, "g.region",
    parameters=list(raster="DEM"))

    and then loop on the sampled points ... involving
      execGRASS("r.viewshed", parameters = list(input = "DEM", output =
    "cumulativeViewshed", max_distance=maxDistance, coordinates =
    as.integer(coords[i,])), flags = c("overwrite" , "b","quiet"))

      and cumulating the viewshed (reading the ouput using
    readRAST("cumulativeViewshed")), all this (loop over the
    points)within a
    function simul() called
    by a
      parSapply(cl,1:nDsimul,simul)


    Here is the error
    Error in checkForRemoteErrors(val) :
       2 nodes produced errors; first error: no such file:
    GRASS_TEMP/file5edb6bf06d70/file5edb4b0cda81/.tmp/geoprocessing/cumulativeViewshed
    Calls: parSapply ... clusterApply -> staticClusterApply ->
    checkForRemoteErrors

    any idea?


The problem is likely that you are working in parallel in the same map 
set. I would suggest to use a separate Mauser for each parallel task 
to write to, read from a different map set which no parallel task is 
writing to, and finally, after all threads are finished, you can 
collect the results from each thread in one map set and delete the 
temporary map sets.

Cheers,

Rainer

    thanks,

    DIdier

    --
    Dr Didier G. Leibovici
        d-d'ye    ley-bow-v-c
    Senior Research Fellow
    Geocomputational Modelling & Geospatial Statistics
    Nottingham Geospatial Institute
    University of Nottingham, UK
    +44 (0)115 84 13924
    http://www.nottingham.ac.uk/ngi/people/didier.leibovici
    Google+ didier.leibovici at gmail.com <javascript:;>
    Skype didierleibovici


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