[R-SIG-Mac] Mac-only problem using readOGR(), which uses ogrInfo(), to read a shapefile from a directory on a USB pen drive

[D G. Rossiter]

I ran across a Mac-only problem using readOGR(), which uses ogrInfo(), to read a shapefile from a directory on a USB pen drive. I tested the behaviour on a Windows 10 machine and did not get the problem. 

Trying to read from the USB drive, with relative and full paths:

> setwd("/Volumes/ISPRS/“) # this is my connected USB drive
> list.files()     
 [1] "map7100.dbf"                      "map7100.prj"                     
 [3] "map7100.sbn"                      "map7100.sbx"                     
[5] "map7100.shp"                      "map7100.shp.xml"                 
[7] "map7100.shx"  
> file.exists("map7100.shp")
[1] TRUE
> usa <- readOGR(dsn=".", layer="map7100")
Error in ogrInfo(dsn = dsn, layer = layer, encoding = encoding, use_iconv = use_iconv,  : 
  Cannot open data source
> usa <- readOGR(dsn="/Volumes/ISPRS", layer="map7100")
Error in ogrInfo(dsn = dsn, layer = layer, encoding = encoding, use_iconv = use_iconv,  : 
  Cannot open data source

But, readOGR reads the shapefile correctly if it’s located on the Mac’s internal drive:

> setwd("/Users/rossiter/data/edu/dgeostats/ex")
> file.exists("./ds/NEweather/map7100.shp")
[1] TRUE
> usa <- readOGR(dsn="./ds/NEweather", layer="map7100")
OGR data source with driver: ESRI Shapefile 
Source: "./ds/NEweather", layer: "map7100"
with 7926 features
It has 19 fields

All packages are up to date. Here is the sessionInfo():

R version 3.3.2 (2016-10-31)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X El Capitan 10.11.6

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

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

other attached packages:
[1] ggplot2_2.2.1  sf_0.3-4       maptools_0.9-1 rgdal_1.2-5   
[5] sp_1.2-4       gstat_1.1-4   

loaded via a namespace (and not attached):
 [1] Rcpp_0.12.9      plyr_1.8.4       xts_0.9-7        tools_3.3.2     
 [5] digest_0.6.12    evaluate_0.10    tibble_1.2       gtable_0.2.0    
 [9] lattice_0.20-34  DBI_0.5-1        yaml_2.1.14      stringr_1.2.0   
[13] knitr_1.15.1     rprojroot_1.2    grid_3.3.2       spacetime_1.2-0 
[17] foreign_0.8-67   rmarkdown_1.3    udunits2_0.13    magrittr_1.5    
[21] backports_1.0.5  scales_0.4.1     intervals_0.15.1 htmltools_0.3.5 
[25] units_0.4-2      rsconnect_0.7    assertthat_0.1   colorspace_1.3-2
[29] labeling_0.3     stringi_1.1.2    lazyeval_0.2.0   munsell_0.4.3   
[33] FNN_1.1          zoo_1.7-14  

This is a problem because several of my students have OS/X machines and like to work from USB-connected external drives.

D G (David) Rossiter
Section of Soil & Crop Sciences
Cornell University
http://www.css.cornell.edu/faculty/dgr2/