PCL 1.8.0 installation: Compile error for including QtGui - ubuntu-14.04

Question

I'm trying to build PCL 1.8.0 on my Ubuntu 14.04 machine from source, following these instructions. But every time I get the following error:
[ 73%] Building CXX object apps/CMakeFiles/pcl_manual_registration.dir/include/pcl/apps/moc_manual_registration.cpp.o
In file included from ~/pcl/release/apps/ui_manual_registration.h:26:0,
from ~/pcl/release/apps/include/pcl/apps/../../../../../apps/include/pcl/apps/manual_registration.h:37,
from ~/pcl/release/apps/include/pcl/apps/moc_manual_registration.cpp:9:
/usr/include/vtk-5.8/QVTKWidget.h:40:25: fatal error: QtGui/QWidget: No such file or directory
#include <QtGui/QWidget>
^
compilation terminated.
make[2]: *** [apps/CMakeFiles/pcl_manual_registration.dir/include/pcl/apps/moc_manual_registration.cpp.o] Error 1
make[1]: *** [apps/CMakeFiles/pcl_manual_registration.dir/all] Error 2
make: *** [all] Error 2
for locate QWidget I get amongst others the following output:
...
/usr/include/qt4/QtGui/QWidget
...
/usr/include/qt5/QtWidgets/QWidget
...
So how can I resolve the error and install pcl?

Answer 1

The problem happens because your configuration is trying to mix Qt4 and Qt5 during PCL build.
According to the link you've provided, PCL is suppossed so be built against Qt4 in this case.
Try to remove everything in release directory and re-initialize CMake config with correct version of Qt.
Like that (following provided example):
cd ~/Documents/pcl
rm -rf relese
mkdir release
cd release
cmake -DCMAKE_BUILD_TYPE=Release -DPCL_QT_VERSION=4 -DBUILD_GPU=ON -DBUILD_apps=ON -DBUILD_examples=ON ..
make