gdalmin

This is a working minimal R package example of using the GDAL C++ API with Rcpp.

It was developed on Ubuntu, and has the following vagaries:

• relies on install of libgdal-dev
• relies on GNU autoconf being installed
• copies the autoconf configure.ac from sf
• copies the Makevars.in from sf

todo

• document required system installs
• use GNU automake/autoconf appropriately, not by copying artefact
• work out cross-platform needs (rwinlib, brewer and so forth)

set up notes

devtools::create("../gdalmin")
devtools::use_readme_rmd()
devtools::use_package_doc()
## useDynLib and importFrom Rccp in package doc
devtools::use_rcpp()

file.copy("inst/extdata/boilerplate/ogr_api_tutorial.cpp", "src/ogr_api.cpp", overwrite = TRUE)
## modify the C++ as below

## copy the contents of 
## https://raw.githubusercontent.com/dis-organization/vapour/master/configure.ac to configure.ac

Change the first line in 'configure.ac' to your C++ file, i.e.

AC_INIT(src/ogr_api.cpp)

Modify src/ogr_api.cpp to include Rcpp, roxygen doc comments, a non-void main C++ function, and a valid path to a shapefile (can have point or anything in it, but the example only prints out point summary, or just a message).

#include <Rcpp.h>
using namespace Rcpp;


#include "ogrsf_frmts.h"
//' OGR API
//'
//' OGR API tutorial minimal example
//' @export
//' @return integer
//' @examples
// [[Rcpp::export]]
int ogr_api()
{
  GDALAllRegister();
  GDALDataset       *poDS;
  poDS = (GDALDataset*) GDALOpenEx( "inst/extdata/shp/point.shp", GDAL_OF_VECTOR, NULL, NULL, NULL );

Run the following

autoconf  ## this will create configure from configure.ac

Now run the following, it creates 'src/init.c'.

tools::package_native_routine_registration_skeleton("../gdalmin", "src/init.c",character_only = FALSE)

Create src/Makevars.in

PKG_CPPFLAGS=@PKG_CPPFLAGS@
PKG_LIBS=@PKG_LIBS@
CXX_STD=CXX11

Make sure roxygen is turned on for build and reload for this package. Now build the package.

Now run it!

library(gdalmin)
ogr_api()

# 1,a,-0.766, -0
# 2,b,0.201, -0
# 3,c,-0.730, -1
# 4,d,-0.142, -0
# 5,e,-0.887, -1
# 6,f,-0.826,  0
# 7,g,0.696, -0
# 8,h,1.421, -0
# 9,i,0.525,  2
# 10,j,-1.022,  1
# [1] 0

Data raw

library(sf)
pt <- st_sf(geometry = st_sfc(lapply(1:10, function(x) st_point(rnorm(2))), crs  = 3031), 
            a = 1:10, b = head(letters, 10))
st_write(pt, "inst/extdata/shp/point.shp")