### Qt4 Installation for GUI

It must be installed before Qwt. A Qt version equal or higher than 4.6 is required. One can install it:

- via YUM:

       yum install qt-devel

- via download from:
  `https://download.qt.io/archive/qt/4.8/4.8.2/qt-everywhere-opensource-src-4.8.2.t ar.gz`

  To install:

      > gunzip qt-everywhere-opensource-src-4.8.2.tar.gz
      > tar xvf qt-everywhere-opensource-src-4.8.2.tar
      > ./configure
      > make
      > make install

  By default Qt4 will be installed in /usr/local/Trolltech/Qt-4.8.2/.

Setup Environment

One has to ensure that `PATH` and `LD_LIBRARY_PATH` have been updated to include Qt4 install path, binaries and libraries. Confirm by executing `qmake -v` and ensuring the result points to Qt4 (not Qt3 or Qt5).

If the environment is not set up, one can add the libraries and executables to the .bashrc by adding `LD_LIBRARY_PATH` and `PATH`:

    export QTDIR=/usr/local/Trolltech/Qt-4.8.2
    export PATH=$QTDIR/bin:$PATH
    export LD_LIBRARY_PATH=$QTDIR/lib:$LD_LIBRARY_PATH