RE : Problem with writeOGR and overwrite_layer=T

On Mon, 14 May 2012, Bastien.Ferland-Raymond at mrnf.gouv.qc.ca wrote:

Dear list,

I have to produce shapefile for a coworker which uses ArcGIS and I've hit a
problem with the writeOGR function from the rgdal package.

I can reproduce the problem on Windows 7 with GDAL 1.9.0, that is, that parts
of shapefiles created by OGR (the *.dbf and *.shp files) cannot be deleted by
poDS->DeleteLayer() - line 473 in rgdal/src/ogrsource.cpp. This also applies
before trying to overwrite them - they cannot be deleted in Windows Explorer
either until the R session exits. Running as administrator does not help
either.

This appears to be an interaction between Windows (7 in my case), GDAL >=
1.8.0, which introduced bans on overwriting for Shapefiles, and possibly some
unknown factors.

This is not a problem I can resolve, certainly not any time soon. It is not
an R code problem as such (I believe), and the stackoverflow speculation is
misleading, this has nothing to do with connections, only with Windows
apparent file usage status.

I would appeal to interested Windows users to contribute a solution - you
will need to be able to cross-compile GDAL for Windows under MSYS, and to
build R packages.

If Windows users know how to unlink files with an incorrect
usage status without exiting R, this would possibly help, but doesn't get us
much further.

Other GDAL/OGR uses such as ogr2ogr exit on error, but it might be helpful to
know if ogr2ogr does the same - that is, is unable to overwrite a layer.
MapInfo File, GML and other drivers do not seem to suffer from the same
issue. Again, checking across a wider range of drivers would help.

Roger

Here is an example:

###

library(rgdal)

Loading required package: sp
Geospatial Data Abstraction Library extensions to R successfully loaded
Loaded GDAL runtime: GDAL 1.9.0, released 2011/12/29
Path to GDAL shared files:
\\sebpriv/usagers/Ferba1/R/R-2.15.0/library/rgdal/gdal
Loaded PROJ.4 runtime: Rel. 4.7.1, 23 September 2009, [PJ_VERSION: 470]
Path to PROJ.4 shared files:
\\sebpriv/usagers/Ferba1/R/R-2.15.0/library/rgdal/proj

sessionInfo()

R version 2.15.0 (2012-03-30)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=French_Canada.1252  LC_CTYPE=French_Canada.1252
LC_MONETARY=French_Canada.1252 LC_NUMERIC=C
LC_TIME=French_Canada.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] rgdal_0.7-8 sp_0.9-98

loaded via a namespace (and not attached):
[1] grid_2.15.0    lattice_0.20-6

setwd("C:\\Documents and Settings\\ferba1\\Bureau\\test rgdal")

# make a basic shape:

coo <-
coordinates(cbind(runif(100,220000,300000),runif(100,5160000,5220000)))
point.shape <-
SpatialPointsDataFrame(coo,data.frame(ID=paste("point",1:100,sep="_")),

+   proj4string = CRS(" +proj=tmerc +lat_0=0 +lon_0=-73.5 +k=0.9999
+x_0=304800 +y_0=0 +datum=NAD83 +units=m +no_defs +ellps=GRS80
+towgs84=0,0,0"))

# now if I try to write itm it works fine for the first 2 shapes:

writeOGR(point.shape,".","point_shape1", driver="ESRI Shapefile")

writeOGR(point.shape,".","point_shape2", driver="ESRI Shapefile" )

# but then if I try to overwrite, it fails:

writeOGR(point.shape,".","point_shape1", driver="ESRI Shapefile",
overwrite_layer=T)

Error in writeOGR(point.shape, ".", "point_shape1", driver = "ESRI
Shapefile",  :
 Creation of output file failed

# Interestingly, it erases 2 files from point_shape1 before failing (the
.prj and the .shx).
# and from now on, it's impossible to create new shapefile:

writeOGR(point.shape,".","point_shape3", driver="ESRI Shapefile" )

Error in writeOGR(point.shape, ".", "point_shape3", driver = "ESRI
Shapefile") :
 Creation of output file failed
###

However, after restarting the whole session and erasing the files created,
and try this new order:

###

writeOGR(point.shape,".","point_shape1", driver="ESRI Shapefile")

writeOGR(point.shape,".","point_shape1", driver="ESRI Shapefile",
overwrite_layer=T)

writeOGR(point.shape,".","point_shape2", driver="ESRI Shapefile" )

writeOGR(point.shape,".","point_shape3", driver="ESRI Shapefile" )

###
Everything works fine.  So two questions arise:

1) why does overwrite_layer doesn't work when the order is changed, can it
be fixed?
2) How to "reset" the writeOGR function after a fail as it seems once it
fails, it get impossible to reuse it in the same session.

After reading this post:
http://stackoverflow.com/questions/6219368/problem-writing-shapefiles-with-writeogr-in-r,
I think it may be some connection issue.  Is there a easy way to close
manually the connection after using writeOGR?  Something like
close.OGR.connection()?

I know maptools::writeSpatialShape can also be used to write shapefile,
however it doesn't write the projection information which I want. It seems
to me that there is a problem with writeOGR, which is a good function so it
could deserve to be fix.

Thanks for your help,

Bastien Ferland-Raymond, M.Sc. Stat., M.Sc. Biol.
Division des orientations et projets sp?ciaux
Direction des inventaires forestiers
Minist?re des Ressources naturelles et de la Faune