-----------------------------
* Copyright
-----------------------------
This software is copyright by CNES - LMD (CNRS/ENS) - NOVELTIS.
Except for the following tcl library used by the GUI:

  BWidget ToolKit
  Copyright 1998-1999 UNIFIX

  Help System
  Copyright 2000-2002 Andrei A. Gratchev

-----------------------------
* Contact
-----------------------------
If you need information on this software, please contact NOVELTIS:

 NOVELTIS
 153, rue du Lac
 F-31670 LABEGE
 France
 http://www.noveltis.com

or go directly to the 4A/OP web site (http://4AOP.noveltis.com/).

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* What is required ?
-----------------------------
The installation of 4A/OP requires the following.

** Software
-----------------------------

*** Standard UNIX/Linux utilities

To build and to use 4A/OP you need utilities available on all flavor of UNIX/Linux.
This concerns, but is not limited to, the following: make, sh, ln, ed, etc.

*** Compilers

You need a Fortran 90 compiler and a C compiler to build the 4A/OP programs.

The supported Fortran 90 compilers are the following (Linux only):
ifort (Intel), gfortran (GNU), pgf90 (PGI).
Fortran compiler is in 64-bit mode but can be changed in 32-bit mode.

The supported C compilers are the following:
gcc (GNU), icc (Intel).
C compiler is in 64-bit.

Important note: 4A/OP-sub has been developed and tested on
a big-endian architecture (Sun). In particular the optical
thickness atlases are big-endian binary files.
On little-endian architecture (i.e. x86 or x64), be sure
your compiler has the option that swaps bytes when file reading.

*** Tcl/Tk

The 4A/OP GUI needs that Tcl/Tk (at least version 8.4) is
installed on your system.
See http://www.tcl.tk for more information on Tcl/Tk.

*** Gnuplot

The visualization part of the 4A/OP GUI needs Gnuplot software
in order to plot graphs. The GUI has been tested with the
following version of Gnuplot: Unix version 4.6.2.
See http://www.gnuplot.info for more information on Gnuplot.

*** NetCDF

The netCDF library (at least version 4.3.1) is required since
the netCDF format is used by 4A/OP.

*** Python

Python 3.8.4 (or a newer version of Python 3) is required to
launch the 4A/OP automatic tests. Python is not required for
running 4A/OP itself.

*** Supported computing environments

Various computing environments have been tested and validated
for the 4A/OP software installation.
The following environements are supported:
Operating System: Linux RedHat/CentOS 7 and 8
Name                    Version (RH7/RH8)
----                    -----------------
GCC                     4.9.3/10.2.0
GFortran                4.9.3/10.2.0
icc                     17.0.2/21.3.0
iFort                   17.0.2/21.3.0
Python                  3.8.4
Tcl/Tk                  8.6.6
GNuplot                 5.0.6/5.4.3
NetCDF                  4.4.1/4.5.4


** Resources
-----------------------------

The 4A/OP installation requires about 16 gigabytes on disk.
In addition, the atlas files can require up to 40 gigabytes of
disk space. This volume depends on the user simulation needs.


-----------------------------
* Installation
-----------------------------
This section describes the installation procedure.

** Summary
-----------------------------
Here are the instructions to build the main installation of
4A/OP.
The working directory for the compilation is srclib/.

*** First of all, the user needs to prepare the compilation
configuration which depends on the compiler that will be used.
The required information (compilers and options/flags) has to
be filled in a makefile available in the srclib sub-directory:
Makefile.4a${IDCOMPIL}.inc, where {IDCOMPIL} is the configuration
identifier of the compilation.

    cd model/srclib

    Edit the configuration file Makefile.4a${IDCOMPIL}.inc with
    IDCOMPIL={own user parameters}

    Adapt the configuration to the user computing environment

    Save this configuration file

*** The compilation command is thus the following:

    make all IDCOMPIL={own user parameters}

The compilation generates librairies, object files and executables.
These compilation outputs are placed in the directory library
/lib${IDCOMPIL}.
The compilation creates also directories used to store the
results of the 4A simulation and the ISRF preparation:
outputbin$IDCOMPIL, outputascii$IDCOMPIL and isrf$IDCOMPIL

Some configuration files come with the distribution:
--> see the 4A/OP "Installation and Quickstart guide" for more
information.

Example:
    make all IDCOMPIL=.gfortran


*** Atlas preparation
The atlas files need to be added if the current archive does
not contain the required atlases.
--> see the 4A/OP "Installation and Quickstart guide" for more
information.

Example:
    rmdir datatl
    ln –s {atlas path} datatl


Alternatively, if the user mainly uses the 4A/OP GUI to
perform simulations, a parameter is available to specify the
atlas directory to be used.
This is the parameter "Atlas database directory" of group
"Atlas" in page "General".


-----------------------------
* How to use 4A/OP ?
-----------------------------

--> see the 4A/OP "Installation and Quickstart guide" to use
4A/OP model (script mode).


Another way to use 4A/OP is to launch its graphical user
interface:

  cd gui
  ./src/4Agui

This program is available in the gui directory of the system installation.
The user can add this directory in his/her PATH or launch 4Agui
from this directory.