Combining two solutions in one using cmake

I have two seperate Visual Studio 2013 solutions and I want to migrate them into one single solution since the first solution (using Qt) serves as the GUI for the second solution.

At the end I would like to have a single solution with a structure like this:

--Solution
-------All Build
-------Project 1
----------------External Dependencies
----------------header files
----------------Source files 
-------Project 2
----------------External Dependencies
----------------header files
----------------Source files

The CMakeLists.txt for the first project is:

cmake_minimum_required(VERSION 2.8.5 FATAL_ERROR)
if(POLICY CMP0025)
  cmake_policy(SET CMP0025 NEW) # CMake 3.0
endif()
if(POLICY CMP0053)
  cmake_policy(SET CMP0053 NEW) # CMake 3.1
endif()

project (Project1)

set(CMAKE_MODULE_PATH 
    ${CMAKE_SOURCE_DIR}/CMake
)

find_package(VTK REQUIRED)
include(${VTK_USE_FILE})

find_package(OpenVR REQUIRED)
find_package(SDL2 REQUIRED)

include_directories(${OPENVR_INCLUDE_DIRS})
include_directories(${SDL2_INCLUDE_DIR})
include_directories(${CMAKE_SOURCE_DIR})

set(HEADER_FILES
    ...
)

set(CODE_FILES
    ...
)


# Copy the obj file to the build directory
file(COPY Data/***.*** DESTINATION ${PROJECT_BINARY_DIR}/Data)
file(COPY Data/***.*** DESTINATION ${PROJECT_BINARY_DIR}/Data)
file(COPY Data/***.*** DESTINATION ${PROJECT_BINARY_DIR}/Data)

#QT5_ADD_RESOURCES(visualization_RCS resources.qrc)

if(VTK_LIBRARIES)
add_executable(${PROJECT_NAME} ${CODE_FILES} ${HEADER_FILES})
  target_link_libraries(${PROJECT_NAME} ${VTK_LIBRARIES} ${SDL2_LIBRARY})  
else()
  message("Specific Libs")
endif()

The CMakeLists.txt for the second project is:

cmake_minimum_required(VERSION 2.8.12)
project(Project2)
find_package(Qt5Widgets)
set(MyProjectLib_src ${PROJECT_SOURCE_DIR}/gui.cpp)
set(MyProjectLib_hdr ${PROJECT_SOURCE_DIR}/gui.h)
set(MyProjectLib_ui  ${PROJECT_SOURCE_DIR}/gui.ui)
set(MyProjectBin_src ${PROJECT_SOURCE_DIR}/main.cpp)
qt5_wrap_cpp(MyProjectLib_hdr_moc ${MyProjectLib_hdr})
qt5_wrap_ui (MyProjectLib_ui_moc  ${MyProjectLib_ui})
include_directories(${PROJECT_SOURCE_DIR})
include_directories(${PROJECT_BINARY_DIR})
add_library(MyProjectLib STATIC 
    ${MyProjectLib_src}
    ${MyProjectLib_hdr_moc}
    ${MyProjectLib_ui_moc}
)
target_link_libraries(MyProjectLib Qt5::Widgets)
add_executable(MyProject ${MyProjectBin_src})
target_link_libraries(MyProject MyProjectLib)

The thing is that i am not able to combine the two CMakeLists.txt into one file. I am stock at this code since days

cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
if(POLICY CMP0025)
  cmake_policy(SET CMP0025 NEW) # CMake 3.0
endif()
if(POLICY CMP0053)
  cmake_policy(SET CMP0053 NEW) # CMake 3.1
endif()

project (project1)

set(CMAKE_MODULE_PATH 
    ${CMAKE_SOURCE_DIR}/CMake
)

find_package(VTK REQUIRED)
include(${VTK_USE_FILE})

find_package (Qt5Widgets REQUIRED)
find_package(OpenVR REQUIRED)
find_package(SDL2 REQUIRED)

include_directories(${OPENVR_INCLUDE_DIRS})
include_directories(${SDL2_INCLUDE_DIR})
include_directories(${CMAKE_SOURCE_DIR})

set(HEADER_FILES
    GPU/header.h
    ...
    ...
)

set(CODE_FILES
    GPU/sourcefile.cxx
    ...
)


#QT5_ADD_RESOURCES(visualization_RCS resources.qrc)
project (project2)


find_package (Qt5Widgets)


set (GuiLib_src Gui/gui.cpp)
set (GuiLib_hdr Gui/gui.h)
set (GuiLib_ui  Gui/gui.ui)
set (GuiBin_src Gui/main.cpp)


qt5_wrap_cpp(GuiLib_hdr_moc ${GuiLib_hdr})
qt5_wrap_ui (GuiLib_ui_moc  ${GuiLib_ui})


include_directories (${PROJECT_SOURCE_DIR})
include_directories (${PROJECT_BINARY_DIR})


add_library (GuiLib STATIC 
    ${GuiLib_src}
    ${GuiLib_hdr_moc}
    ${GuiLib_ui_moc}
)
target_link_libraries (GuiLib Qt5::Widgets)



if(VTK_LIBRARIES)
  add_executable(${PROJECT_NAME} ${CODE_FILES} ${HEADER_FILES})
  target_link_libraries(${PROJECT_NAME} ${VTK_LIBRARIES} ${SDL2_LIBRARY})  #Qt5::Core Qt5::Gui
  add_executable(Gui ${GuiBin_src})
  target_link_libraries (Gui GuiLib)
else()
  message("Specific Libs")
endif()

It is worth mentioning that project1 is using VTK, OpenVR and SDL, while project2 is just using Qt 5.

The easiest solution to satisfy the requirements you have outlined in the question is to introduce a new CMakeList file in Solution/CMakeLists.txt:

cmake_minimum_required(VERSION 2.8.12)
project(NameForTheCombinedProject)

add_subdirectory(path/to/project1/dir)
add_subdirectory(path/to/project2/dir)

In addition, you'll have to change all references to CMAKE_SOURCE_DIR and CMAKE_BINARY_DIR in the projects to CMAKE_CURRENT_SOURCE_DIR and CMAKE_CURRENT_BINARY_DIR, respectively. In particular, this affects the commands set(CMAKE_MODULE_PATH ...) and file(COPY ...) in Project 1.

The reason is that now CMAKE_SOURCE_DIRand CMAKE_BINARY_DIR will refer to the directories of the toplevel (newly created) project.