[osg-qt]how to use it in an cmakelist.txt ?

[yanzixiang]

osg-qt provides pkg-config modules:

  # osgQt utility library.
  openscenegraph-osgQt

but when i try to

find_package(PkgConfig REQUIRED)
pkg_check_modules(openscenegraph-osgQt REQUIRED IMPORTED_TARGET OSGQT)

it's said said

Could NOT find PkgConfig (missing: PKG_CONFIG_EXECUTABLE)

  Hint: The project() command has not yet been called.  It sets up
  system-specific search paths.

so,how can i use it in an cmakelist.txt ?