* create a build folder at the same level as axel:
```shell
mkdir ../build-axl
cd ../build-axl
```
* configure with cmake
```shell
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:
```shell
ccmake ../axel*-DVTK_DIR=$PWD/../build-vtk
```
and setup the variable `QT_QMAKE_EXECUTABLE` to the path to `qmake`.