How to load a geospatial pdf in R? - r

Question

I am new handling spatial data, and newer doing it in R.
My last attemp was trying to read data in a geographical pdf format. It is information about mexican political bourdaries, so polygons, the file.
I tryied to use the rgdal package to read the data. After typing ogrDrivers()[40:45,], which show the drivers available, I got.
name write
40 PCIDSK TRUE
41 PDF TRUE
42 PDS FALSE
43 PGDump TRUE
44 PGeo FALSE
45 PostgreSQL TRUE
The result show that there is a driver for PDF's, but trying the usual way to read files readOGR(dsn = "data source name", layer = "LAYER") produces:
Error in ogrInfo(dsn = dsn, layer = layer, encoding = encoding, use_iconv = use_iconv, :
Cannot open file
The help of the function does not say the values expected neither for dsn nor for layer when the file is in a geospatial pdf format.
Does anybody knows a way to import data from a pdf? this is from geospatial format; I would appreciate any answer.
By the way, I have Ubuntu 14.04.3 with Qgis installed, and the latest versions of R and rgeos.

Answer 1

The dsn is the file path, and the layer name is internal to the PDF. You can get a list of layers with ogrListLayers on the file name:
> ogrListLayers("foo.pdf")
[1] "polys"
attr(,"driver")
[1] "PDF"
attr(,"nlayers")
[1] 1
Ugly output, but that's one layer called polys. So I can read it like this:
> polys = readOGR("./foo.pdf","polys")
OGR data source with driver: PDF
Source: "./foo.pdf", layer: "polys"
with 9 features
It has 1 fields
Note that this only applies to a special class of PDF files with the map data stored in a particular way. Just because your PDF has a map in it, doesn't make it a Geospatial PDF. Here's the command line test on my Geospatial PDF:
$ ogrinfo Monaco/foo.pdf
Had to open data source read-only.
INFO: Open of `Monaco/foo.pdf'
using driver `PDF' successful.
1: polys (Polygon)
and here's the test on yours:
$ ogrinfo CED06_CARTA_110614.pdf
FAILURE:
Unable to open datasource `CED06_CARTA_110614.pdf' with the following drivers.
-> ESRI Shapefile
-> MapInfo File
[etc etc]
-> PDF
[etc etc]
So you dont have a Geospatial PDF.
Your options are, in possible order of simplicity, something like:
Get the boundary data in a GIS data format (eg shapefile, GeoPDF)
Save as an image, load into a GIS, georeference and trace it (QGIS can do this)
Get the raw PDF vectors out of the PDF, assuming they are vectors (first glance shows me the map isn't an image), then find the right transformation to whatever coordinate system, then possibly rebuild the topology if all you have is line segments...
I've had a little bit of success using pstoedit to convert the PDF to a DXF file which can be loaded into QGIS, but then you have to clean it up and reconstruct the polygons, and then its still not in the right geographical location. It would be much simpler if you can get a shapefile of the regions you are interested in.
If what you want is a raster version of the PDF, then you can either use raster::stack("file.pdf") or readGDAL("file.pdf"). But you'll get an image with no georeferencing (it'll just have a bounding box of the number of pixels) since there's no coordinate system with the PDF.