migrating to catkin: undefined reference from header file

edit

I'm trying to catkinize the people stack, and am getting undefined references to things in a header file in the face_detector package.

CMakeLists.txt:

cmake_minimum_required(VERSION 2.8.3)
project(face_detector)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  geometry_msgs
  std_srvs
  cv_bridge
  stereo_msgs
  sensor_msgs
  tf
  rosbag
  image_transport
  people_msgs
  image_geometry
  genmsg
  actionlib_msgs)

find_package(Boost REQUIRED COMPONENTS signals system thread)
find_package(OpenCV)

include_directories(
  include
  ${Boost_INCLUDE_DIRS}
  ${OpenCV_INCLUDE_DIRS}
  ${catkin_INCLUDE_DIRS})

#set the default path for built executables to the "bin" directory
set(EXECUTABLE_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/bin)
#set the default path for built libraries to the "lib" directory
set(LIBRARY_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/lib)

add_action_files(
  DIRECTORY action
  FILES FaceDetector.action
)
generate_messages(DEPENDENCIES actionlib_msgs people_msgs)

add_executable(face_detector
                       src/face_detection.cpp 
                       src/faces.cpp)
target_link_libraries(${PROJECT_NAME}
  ${catkin_LIBRARIES}
  ${Boost_LIBRARIES}
  ${OpenCV_LIBRARIES})

catkin_package(INCLUDE_DIRS include
  CATKIN_DEPENDS people_msgs geometry_msgs)

Errors:

CMakeFiles/face_detector.dir/src/face_detection.cpp.o: In function `people::FaceDetector::FaceDetector(std::string)':
face_detection.cpp:(.text._ZN6people12FaceDetectorC2ESs[_ZN6people12FaceDetectorC5ESs]+0xd49): undefined reference to `people::Faces::FACE_SIZE_MIN_M'
face_detection.cpp:(.text._ZN6people12FaceDetectorC2ESs[_ZN6people12FaceDetectorC5ESs]+0xdb6): undefined reference to `people::Faces::FACE_SIZE_MAX_M'
face_detection.cpp:(.text._ZN6people12FaceDetectorC2ESs[_ZN6people12FaceDetectorC5ESs]+0xe23): undefined reference to `people::Faces::MAX_FACE_Z_M'
face_detection.cpp:(.text._ZN6people12FaceDetectorC2ESs[_ZN6people12FaceDetectorC5ESs]+0xe90): undefined reference to `people::Faces::FACE_SEP_DIST_M'
collect2: error: ld returned 1 exit status
make[2]: *** [/home/lazewatd/people_ws/devel/lib/face_detector/face_detector] Error 1
make[1]: *** [people/face_detector/CMakeFiles/face_detector.dir/all] Error 2
make: *** [all] Error 2
Invoking "make" failed

A few things to note:

• this worked fine with rosbuild in hydro
• I know it can find the header file - if I remove/change include from include_directories, it complains about not being able to find it way earlier

UPDATE:

Now I'm even more confused. The first example works, but the second leads to the linker errors above:

namespace people {
    //works
    double fsmm = Faces::FACE_SIZE_MIN_M;
    local_nh.param("face_size_min_m",face_size_min_m,fsmm);

    //doesn't work
    local_nh.param("face_size_min_m",face_size_min_m,Faces::FACE_SIZE_MIN_M);
}