title: Install udunits2 package for R3.3
body: <p>I just wasted the whole day trying to figure out how to install the udunits2 package to be able to install the units package to be able to install the ggforce and ggraph packages.</p>
  
  <p>I'm trying to install it on Ubuntu 16.04, and R >= 3.3 since ggforce was built under R 3.3. </p>
  
  <p>I followed these instructions here:
  <a href="https://github.com/edzer/units/issues/1" rel="noreferrer">https://github.com/edzer/units/issues/1</a></p>
  
  <p>Although I have libudunits-2.0 and udunits installed on my machine (as sudo apt-get install udunits2 doesn't find a udunits2 package), and the PATH to the libudunits-2 and udunits locations on my $PATH, in R when I try installing udunits2, units or ggforce I'm getting an error that says,</p>
  
  <pre><code>--* installing *source* package ‘udunits2’ ...
  ** package ‘udunits2’ successfully unpacked and MD5 sums checked
  checking for gcc... gcc
  checking whether the C compiler works... yes
  checking for C compiler default output file name... a.out
  checking for suffix of executables... 
  checking whether we are cross compiling... no
  checking for suffix of object files... o
  checking whether we are using the GNU C compiler... yes
  checking whether gcc accepts -g... yes
  checking for gcc option to accept ISO C89... none needed
  checking for XML_ParserCreate in -lexpat... yes
  checking how to run the C preprocessor... gcc -E
  checking for grep that handles long lines and -e... /bin/grep
  checking for egrep... /bin/grep -E
  checking for ANSI C header files... yes
  checking for sys/types.h... yes
  checking for sys/stat.h... yes
  checking for stdlib.h... yes
  checking for string.h... yes
  checking for memory.h... yes
  checking for strings.h... yes
  checking for inttypes.h... yes
  checking for stdint.h... yes
  checking for unistd.h... yes
  checking udunits2.h usability... no
  checking udunits2.h presence... no
  checking for udunits2.h... no
  checking for ut_read_xml in -ludunits2... no
  -----Error: libudunits2.a not found-----
       If the udunits2 library is installed in a non-standard location,
       use --configure-args='--with-udunits2-lib=/usr/local/lib' for   
       example,
       or --configure-args='--with-udunits2-include=/usr/include/udunits2'
       replacing paths with appropriate values for your installation.
       You can alternatively use the UDUNITS2_INCLUDE and UDUNITS2_LIB
       environment variables.
       If udunits2 is not installed, please install it.
       It is required for this package.
       ERROR: configuration failed for package ‘udunits2’
  * removing ‘/home/fjay/R/x86_64-pc-linux-gnu-library/3.3/udunits2’
  * restoring previous ‘/home/fjay/R/x86_64-pc-linux-gnu-library 
  /3.3/udunits2’
  
  The downloaded source packages are in
      ‘/tmp/Rtmp0syxnJ/downloaded_packages’
  Warning message:
  In install.packages("udunits2", lib = "/home/fjay/R/x86_64-pc-linux-
   gnu-library/3.3") :
   installation of package ‘udunits2’ had non-zero exit status
  &gt;
  </code></pre>
  
  <p>So, umm, it's looking for the udunits2.h and libudunits2.a files....
  So, I downloaded udunits2 from CRAN, unpacked it and put it in my R library.
  Then, if I put library(udunits2, lib.loc = "my library dir") I get an error saying it's not installed. So, when I install.package('udunits2', repo = NULL, libconfig.args = '--with-udunits2-lib=/home/fjay/R/x86_64-pc-linux-gnu-library/3.3') or install.packages('units',....) or install.packages('ggforce',...) it is still looking for these files...and, after inspection of the udunits2 package these files are not in any of the udunits2 folders.</p>
  
  <p>If anyone knows how to install this udunits2 packages please help me! </p>