6/2021   Notes on installing cygwin on Windows 10

go to cygwin.com
run setup-x86-64.exe  (need system admin)  
  (64-bits is needed for wgrib2 to process files > 2GB)
  (I installed from the internet)
  (I installed all recommended packages)
  (I installed icons in both locations)

The rest is run from cygwin's bash (click on Cygwin Terminal icon)


See if you have gcc, gfortran, g++, and make installed.

   gcc
     (if you see gcc: command not found, you need to download gcc and gfortran)
       (go to cygwin.com, run setup-x86-64.exe)
       (select packages: view:full search: gcc-fortran, I selected the latest version)

   gfortran
     (if you see gfortran: command not found, you need to download gfortran, see above)
       (go to cygwin.com, run setup-x86-64.exe)
       (select packages: view:full search: gcc-fortran, I selected the latest version)

   make
     (if you see make: command not found, you need to download make, if nothing happens, 
       type control-c to quit the make program)
       (go to cygwin.com, run setup-x86-64.exe)
       (select packages: view:full search: make, I selected latest version)

   g++
     (if you see g++: command not found, you need to download gcc-g++)
       (go to cygwin.com, run setup-x86-64.exe)
       (select packages: view:full search: gcc-g++, I selected latest version)


Get wgrib2 source code and install.

get wgrib2.tgz from ftp.cpc.ncep.noaa.gov/wd51we/wgrib2/wgrib2.tgz
If you use a browser to download wgrib2.tgz, you can find the download in

   /cygdrive/c/Users/YourName/Downloads/wgrib2.tgz
   (copy to home directory using bash)
   mv /cygdrive/c/Users/YourName/Downloads/wgrib2.tgz  ~


Of course "/cygdrive/c" could be replaced by "/cygdrive/d" if your
windows home directory is on "d:".

The rest is run from cygwin's bash (run Cygwin Terminal icon)

   cd
   (cd to your home directory)

   tar -xzvf wgrib2.tgz
   (expand wgrib2.tgz, now you should see the grib2 directory)

   cd grib2


Compile

   export CC=gcc
   export FC=gfortran
   (you may want to alter the "makefile" to make a custom configuration)
   make
   (this should make wgrib2/wgrib2.exe)


2/23/2021: wgrib2 v3.0.1+ Cygwin and zlib

The makefile can make a shared wgrib2 library which is used to run pywgrib2.
However, zlib creates an unresolved reference to the symbol _wopen.  This 
provents the shared library from being used with pywgrib2.  So for a shared 
library, you cannot use png or jpeg2000 compression. To build the shared
library you must set

   USE_JASPER=0
   USE_OPENJPEG=0
   USE_PNG=0

Pywgrib2 has no support for jpeg2000 or png compression.