Before starting the compilation of the sources, see here for the requirements.
If qmake is not in the path the following command can be used, before configuring axel:
To configure axel,
cmake ../axel -DVTK_DIR=$PWD/../build-vtk
If VTK has been built in the folder $PWD/../build-vtk. The option -DVTK_DIR=path_to_buid_of_vtk specifies the path to the directory where VTK has been built.
If Qt is not found you may set manually the path to qmake, using ccmake (instead of cmake) as follows:
ccmake ../axel* -DVTK_DIR=$PWD/../build-vtk
and setup the variable QT_QMAKE_EXECUTABLE to the path to qmake.