[GRASS-stats] Mapset and layer names in readVECT using GRASS GDAL plugin

[Roger Bivand]

Hi,

Thanks for your interest. I do not use the plugins at all, as they have 
historically led to great difficulty in managing and maintaining rgdal (I 
sometimes rebuild GDAL more than once a day). If you would like commit 
rights on R-Forge, please file a request there, and we can try to find 
ways of automating checking (or testing) the functionality, but without my 
contribution.

Best wishes,

Roger

On Thu, 18 Jun 2015, Ahmadou Dicko wrote:

> Hi,
>
> I'm trying to use the direct OGR access to GRASS vector using plugin
> through the rgrass7 package in R but I have some issues with the
> mapset argument.
>
> Here are the steps to reproduce the bug using the nc_basic_spm_grass7
> GRASS location and user1 mapset.
>
> Within the GRASS session, we launch R
> library(rgrass7)
> v <- readVECT("geonames", plugin = TRUE)
> Error in .read_vect_plugin(vname = vname, layer = layer, type = type,  :
>  object 'mapset' not found
>
> One way to fix this, is to add a mapset argument to .read_vect_plugin
> and set it by default to the same argument in the readVECT function.
>
> ### Example of fix
> readVECT <- function(..., mapset = NULL, ...) {
> ....
>         if (plugin) {
>            res <- .read_vect_plugin(..., mapset = mapset, ...)
> ....
> }
>
> But once this problem solved, another one appears. This one, need
> confirmation though. Using the GRASS GDAL plugin, I can't open a GRASS
> vector without using the layer name. I am aware that we can use the
> layer number using other driver (Shapefiles, GML, etc) but I looks
> like (at least in my setup) that I can't open it without giving the
> layer name.
>
> I modified rgrass7:::.read_vect_plugin and named it .read_vect_plugin2
> and added a mapset argument (to correct the first bug).
>
> ### Reproducing the error
> sss <- strsplit(packageDescription("rgdal")$Version, "-")[[1]]
>
> class(
> .read_vect_plugin2("geonames",
>                    mapset = NULL,
>                    layer = 1L,
>                    sss = sss,
>                    ignore.stderr = TRUE,
>                    pointDropZ = TRUE)
> )
> Error in ogrInfo(dsn = dsn, layer = layer, encoding = encoding,
> use_iconv = use_iconv,  :
>  Cannot open layer
>
>
> class(
> .read_vect_plugin2("geonames",
>                     mapset = NULL,
>                     layer = "geonames",
>                     sss = sss,
>                     ignore.stderr = TRUE,
>                     pointDropZ = TRUE)
> )
> [1] "SpatialPointsDataFrame"
> attr(,"package")
> [1] "sp"
>
> Please can you confirm that it is a feature of the plugin to have the
> real name instead of the layer number ?
>
> Nonetheless, one way to fix this is to add a call to
> rgdal::ogrListLayers in the rgrass7:::.read_vect_plugin
>
>    dsn <- paste(gg$GISDBASE, gg$LOCATION_NAME, mapset, "vector",
>                 vname[1], "head", sep = "/")
>    layers <- rgdal::ogrListLayers(dsn = dsn)
>
> Using this approach we can have the layer names and use it in readOGR.
> I hope that I described it clearly.
>
> Best regards,
>
> Info and spec
> Linux:
> Linux dickoa 4.0.5-1-ARCH #1 SMP PREEMPT Sat Jun 6 18:37:49 CEST 2015
> x86_64 GNU/Linux
>
> GRASS:
> version=7.1.svn
> date=2015
> revision=65487
> build_date=2015-06-16
> build_platform=x86_64-unknown-linux-gnu
>
> GDAL:
> GDAL 1.11.2, released 2015/02/10
>
>
> R:
> sessionInfo()
> R version 3.2.1 RC (2015-06-14 r68519)
> Platform: x86_64-unknown-linux-gnu (64-bit)
> Running under: Arch Linux
>
> locale:
> [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
> [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
> [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
> [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
> [9] LC_ADDRESS=C               LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods
> [7] base
>
> other attached packages:
> [1] rgdal_0.9-3   rgrass7_0.1-0 XML_3.98-1.2  sp_1.1-1
>
> loaded via a namespace (and not attached):
> [1] tools_3.2.1     grid_3.2.1      lattice_0.20-31
>
>
>
> -- 
> Ahmadou H. DICKO
> statistician economist (Ingénieur Statisticien Économiste)
> PhD candidate in Climate change economics
> Faculty of economics and managment - Cheikh Anta Diop University
> West African Science Service Center on Climate Change and Adaptated
> Land Use (WASCAL)
> Center for Development Research (ZEF) - University of Bonn
> email : ahmadou.dicko at ucad.edu.sn
> twitter : @dickoah
> github : github/dickoa
> tel : +221 33 827 55 16
> portable: +221 77 123 81 69
> _______________________________________________
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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no