# Building & Installation

## Getting the source code

You can start with the latest stable release . Or if you want the latest version, you can clone the git repository

    git clone https://ceres-solver.googlesource.com/ceres-solver

## Dependencies

Ceres relies on a number of open source libraries, some of which are optional. For details on customizing the build process, see Customizing the build .

- Eigen 3.2.2 or later strongly recommended, 3.1.0 or later required.

  Note

  Ceres can also use Eigen as a sparse linear algebra library. Please see the documentation for `EIGENSPARSE` for more details.

- CMake 2.8.0 or later. Required on all platforms except for Android.

- Google Log 0.3.1 or later. Recommended

  Note

  Ceres has a minimal replacement of `glog` called `miniglog` that can be enabled with the `MINIGLOG` build option. `miniglog` is needed on Android as `glog` currently does not build using the NDK. It can however be used on other platforms too.

  We do not advise using `miniglog` on platforms other than Android due to the various performance and functionality compromises in `miniglog`.

  Note

  If you are compiling `glog` from source, please note that currently, the unit tests for `glog` (which are enabled by default) do not compile against a default build of `gflags` 2.1 as the gflags namespace changed from `google::` to `gflags::`. A patch to fix this is available from here.

- Google Flags. Needed to build examples and tests.

- SuiteSparse. Needed for solving large sparse linear systems. Optional; strongly recomended for large scale bundle adjustment

- CXSparse. Similar to `SuiteSparse` but simpler and slower. CXSparse has no dependencies on `LAPACK` and `BLAS`. This makes for a simpler build process and a smaller binary. Optional

- BLAS and LAPACK routines are needed by `SuiteSparse`, and optionally used by Ceres directly for some operations.

  On `UNIX` OSes other than Mac OS X we recommend ATLAS, which includes `BLAS` and `LAPACK` routines. It is also possible to use OpenBLAS . However, one needs to be careful to turn off the threading inside `OpenBLAS` as it conflicts with use of threads in Ceres.

  Mac OS X ships with an optimized `LAPACK` and `BLAS` implementation as part of the `Accelerate` framework. The Ceres build system will automatically detect and use it.

  For Windows things are much more complicated. LAPACK For Windows has detailed instructions..

  Optional but required for `SuiteSparse`.

## Linux

We will use Ubuntu as our example linux distribution.

Note

Up to at least Ubuntu 14.04, the SuiteSparse package in the official package repository (built from SuiteSparse v3.4.0) cannot be used to build Ceres as a shared library. Thus if you want to build Ceres as a shared library using SuiteSparse, you must perform a source install of SuiteSparse or use an external PPA (see bug report here). It is recommended that you use the current version of SuiteSparse (4.2.1 at the time of writing).

Start by installing all the dependencies.

    # CMake
    sudo apt-get install cmake
    # google-glog + gflags
    sudo apt-get install libgoogle-glog-dev
    # BLAS & LAPACK
    sudo apt-get install libatlas-base-dev
    # Eigen3
    sudo apt-get install libeigen3-dev
    # SuiteSparse and CXSparse (optional)
    # - If you want to build Ceres as a *static* library (the default)
    #   you can use the SuiteSparse package in the main Ubuntu package
    #   repository:
    sudo apt-get install libsuitesparse-dev
    # - However, if you want to build Ceres as a *shared* library, you must
    #   add the following PPA:
    sudo add-apt-repository ppa:bzindovic/suitesparse-bugfix-1319687
    sudo apt-get update
    sudo apt-get install libsuitesparse-dev

We are now ready to build, test, and install Ceres.

    tar zxf ceres-solver-1.11.0.tar.gz
    mkdir ceres-bin
    cd ceres-bin
    cmake ../ceres-solver-1.11.0
    make -j3
    make test
    # Optionally install Ceres, it can also be exported using CMake which
    # allows Ceres to be used without requiring installation, see the documentation
    # for the EXPORT_BUILD_DIR option for more information.
    make install

You can also try running the command line bundling application with one of the included problems, which comes from the University of Washington’s BAL dataset [Agarwal].

    bin/simple_bundle_adjuster ../ceres-solver-1.11.0/data/problem-16-22106-pre.txt

This runs Ceres for a maximum of 10 iterations using the `DENSE_SCHUR` linear solver. The output should look something like this.

    iter      cost      cost_change  |gradient|   |step|    tr_ratio  tr_radius  ls_iter  iter_time  total_time
       0  4.185660e+06    0.00e+00    1.09e+08   0.00e+00   0.00e+00  1.00e+04       0    7.59e-02    3.37e-01
       1  1.062590e+05    4.08e+06    8.99e+06   5.36e+02   9.82e-01  3.00e+04       1    1.65e-01    5.03e-01
       2  4.992817e+04    5.63e+04    8.32e+06   3.19e+02   6.52e-01  3.09e+04       1    1.45e-01    6.48e-01
       3  1.899774e+04    3.09e+04    1.60e+06   1.24e+02   9.77e-01  9.26e+04       1    1.43e-01    7.92e-01
       4  1.808729e+04    9.10e+02    3.97e+05   6.39e+01   9.51e-01  2.78e+05       1    1.45e-01    9.36e-01
       5  1.803399e+04    5.33e+01    1.48e+04   1.23e+01   9.99e-01  8.33e+05       1    1.45e-01    1.08e+00
       6  1.803390e+04    9.02e-02    6.35e+01   8.00e-01   1.00e+00  2.50e+06       1    1.50e-01    1.23e+00

    Ceres Solver v1.11.0 Solve Report
    ----------------------------------
                                         Original                  Reduced
    Parameter blocks                        22122                    22122
    Parameters                              66462                    66462
    Residual blocks                         83718                    83718
    Residual                               167436                   167436

    Minimizer                        TRUST_REGION

    Dense linear algebra library            EIGEN
    Trust region strategy     LEVENBERG_MARQUARDT

                                            Given                     Used
    Linear solver                     DENSE_SCHUR              DENSE_SCHUR
    Threads                                     1                        1
    Linear solver threads                       1                        1
    Linear solver ordering              AUTOMATIC                22106, 16

    Cost:
    Initial                          4.185660e+06
    Final                            1.803390e+04
    Change                           4.167626e+06

    Minimizer iterations                        6
    Successful steps                            6
    Unsuccessful steps                          0

    Time (in seconds):
    Preprocessor                            0.261

      Residual evaluation                   0.082
      Jacobian evaluation                   0.412
      Linear solver                         0.442
    Minimizer                               1.051

    Postprocessor                           0.002
    Total                                   1.357

    Termination:                      CONVERGENCE (Function tolerance reached. |cost_change|/cost: 1.769766e-09 <= 1.000000e-06)

## Mac OS X

Note

Ceres will not compile using Xcode 4.5.x (Clang version 4.1) due to a bug in that version of Clang. If you are running Xcode 4.5.x, please update to Xcode >= 4.6.x before attempting to build Ceres.

On OS X, you can either use MacPorts or Homebrew to install Ceres Solver.

If using MacPorts, then

    sudo port install ceres-solver

will install the latest version.

If using Homebrew and assuming that you have the `homebrew/science` [1] tap enabled, then

    brew install ceres-solver

will install the latest stable version along with all the required dependencies and

    brew install ceres-solver --HEAD

will install the latest version in the git repo.

You can also install each of the dependencies by hand using Homebrew. There is no need to install `BLAS` or `LAPACK` separately as OS X ships with optimized `BLAS` and `LAPACK` routines as part of the vecLib framework.

    # CMake
    brew install cmake
    # google-glog and gflags
    brew install glog
    # Eigen3
    brew install eigen
    # SuiteSparse and CXSparse
    brew install suite-sparse

We are now ready to build, test, and install Ceres.

    tar zxf ceres-solver-1.11.0.tar.gz
    mkdir ceres-bin
    cd ceres-bin
    cmake ../ceres-solver-1.11.0
    make -j3
    make test
    # Optionally install Ceres, it can also be exported using CMake which
    # allows Ceres to be used without requiring installation, see the
    # documentation for the EXPORT_BUILD_DIR option for more information.
    make install

Like the Linux build, you should now be able to run `bin/simple_bundle_adjuster`.

Footnotes

[1] | Ceres and many of its dependencies are in homebrew/science tap. So, if you don’t have this tap enabled, then you will need to enable it as follows before executing any of the commands in this section.
    brew tap homebrew/science

## Windows

Note

If you find the following CMake difficult to set up, then you may be interested in a Microsoft Visual Studio wrapper for Ceres Solver by Tal Ben-Nun.

On Windows, we support building with Visual Studio 2010 or newer. Note that the Windows port is less featureful and less tested than the Linux or Mac OS X versions due to the lack of an officially supported way of building SuiteSparse and CXSparse. There are however a number of unofficial ways of building these libraries. Building on Windows also a bit more involved since there is no automated way to install dependencies.

Note

Using `google-glog` & `miniglog` with windows.h.

The windows.h header if used with GDI (Graphics Device Interface) defines `ERROR`, which conflicts with the definition of `ERROR` as a LogSeverity level in `google-glog` and `miniglog`. There are at least two possible fixes to this problem:

1. Use `google-glog` and define `GLOG_NO_ABBREVIATED_SEVERITIES` when building Ceres and your own project, as documented here. Note that this fix will not work for `miniglog`, but use of `miniglog` is strongly discouraged on any platform for which `google-glog` is available (which includes Windows).
2. If you do not require GDI, then define `NOGDI` before including windows.h. This solution should work for both `google-glog` and `miniglog` and is documented for `google-glog` here.

1. Make a toplevel directory for deps & build & src somewhere: `ceres/`

2. Get dependencies; unpack them as subdirectories in `ceres/` (`ceres/eigen`, `ceres/glog`, etc)

   1. `Eigen` 3.1 (needed on Windows; 3.0.x will not work). There is no need to build anything; just unpack the source tarball.
   2. `google-glog` Open up the Visual Studio solution and build it.
   3. `gflags` Open up the Visual Studio solution and build it.
   4. (Experimental) `SuiteSparse` Previously SuiteSparse was not available on Windows, recently it has become possible to build it on Windows using the suitesparse-metis-for-windows project. If you wish to use `SuiteSparse`, follow their instructions for obtaining and building it.
   5. (Experimental) `CXSparse` Previously CXSparse was not available on Windows, there are now several ports that enable it to be, including: [1] and [2]. If you wish to use `CXSparse`, follow their instructions for obtaining and building it.

3. Unpack the Ceres tarball into `ceres`. For the tarball, you should get a directory inside `ceres` similar to `ceres-solver-1.3.0`. Alternately, checkout Ceres via `git` to get `ceres-solver.git` inside `ceres`.

4. Install `CMake`,

5. Make a dir `ceres/ceres-bin` (for an out-of-tree build)

6. Run `CMake`; select the `ceres-solver-X.Y.Z` or `ceres-solver.git` directory for the CMake file. Then select the `ceres-bin` for the build dir.

7. Try running `Configure`. It won’t work. It’ll show a bunch of options. You’ll need to set:

   1. `EIGEN_INCLUDE_DIR_HINTS`
   2. `GLOG_INCLUDE_DIR_HINTS`
   3. `GLOG_LIBRARY_DIR_HINTS`
   4. `GFLAGS_INCLUDE_DIR_HINTS`
   5. `GFLAGS_LIBRARY_DIR_HINTS`
   6. (Optional) `SUITESPARSE_INCLUDE_DIR_HINTS`
   7. (Optional) `SUITESPARSE_LIBRARY_DIR_HINTS`
   8. (Optional) `CXSPARSE_INCLUDE_DIR_HINTS`
   9. (Optional) `CXSPARSE_LIBRARY_DIR_HINTS`

   to the appropriate directories where you unpacked/built them. If any of the variables are not visible in the `CMake` GUI, create a new entry for them. We recommend using the `<NAME>_(INCLUDE/LIBRARY)_DIR_HINTS` variables rather than setting the `<NAME>_INCLUDE_DIR` & `<NAME>_LIBRARY` variables directly to keep all of the validity checking, and to avoid having to specify the library files manually.

8. You may have to tweak some more settings to generate a MSVC project. After each adjustment, try pressing Configure & Generate until it generates successfully.

9. Open the solution and build it in MSVC

To run the tests, select the `RUN_TESTS` target and hit Build RUN_TESTS from the build menu.

Like the Linux build, you should now be able to run `bin/simple_bundle_adjuster`.

Notes:

1. The default build is Debug; consider switching it to release mode.
2. Currently `system_test` is not working properly.
3. CMake puts the resulting test binaries in `ceres-bin/examples/Debug` by default.
4. The solvers supported on Windows are `DENSE_QR`, `DENSE_SCHUR`, `CGNR`, and `ITERATIVE_SCHUR`.
5. We’re looking for someone to work with upstream `SuiteSparse` to port their build system to something sane like `CMake`, and get a fully supported Windows port.

## Android

Download the `Android NDK` version `r9d` or later. Run `ndk-build` from inside the `jni` directory. Use the `libceres.a` that gets created.

## iOS

Note

You need iOS version 7.0 or higher to build Ceres Solver.

To build Ceres for iOS, we need to force `CMake` to find the toolchains from the iOS SDK instead of using the standard ones. For example:

    cmake \
    -DCMAKE_TOOLCHAIN_FILE=../ceres-solver/cmake/iOS.cmake \
    -DEIGEN_INCLUDE_DIR=/path/to/eigen/header \
    -DIOS_PLATFORM=<PLATFORM> \
    <PATH_TO_CERES_SOURCE>

`PLATFORM` can be: `OS`, `SIMULATOR` or `SIMULATOR64`. You can build for `OS` (`armv7`, `armv7s`, `arm64`), `SIMULATOR` (`i386`) or `SIMULATOR64` (`x86_64`) separately and use `lipo` to merge them into one static library. See `cmake/iOS.cmake` for more options.

After building, you will get a `libceres.a` library, which you will need to add to your Xcode project.

The default CMake configuration builds a bare bones version of Ceres Solver that only depends on Eigen (`MINIGLOG` is compiled into Ceres if it is used), this should be sufficient for solving small to moderate sized problems (No `SPARSE_SCHUR`, `SPARSE_NORMAL_CHOLESKY` linear solvers and no `CLUSTER_JACOBI` and `CLUSTER_TRIDIAGONAL` preconditioners).

If you decide to use `LAPACK` and `BLAS`, then you also need to add `Accelerate.framework` to your Xcode project’s linking dependency.

## Customizing the build

It is possible to reduce the libraries needed to build Ceres and customize the build process by setting the appropriate options in `CMake`. These options can either be set in the `CMake` GUI, or via `-D<OPTION>=<ON/OFF>` when running `CMake` from the command line. In general, you should only modify these options from their defaults if you know what you are doing.

Note

If you are setting variables via `-D<VARIABLE>=<VALUE>` when calling `CMake`, it is important to understand that this forcibly overwrites the variable `<VARIABLE>` in the `CMake` cache at the start of every configure.

This can lead to confusion if you are invoking the `CMake` curses terminal GUI (via `ccmake`, e.g. ``ccmake -D<VARIABLE>=<VALUE> <PATH_TO_SRC>`). In this case, even if you change the value of `<VARIABLE>` in the `CMake` GUI, your changes will be overwritten with the value passed via `-D<VARIABLE>=<VALUE>` (if one exists) at the start of each configure.

As such, it is generally easier not to pass values to `CMake` via `-D` and instead interactively experiment with their values in the `CMake` GUI. If they are not present in the Standard View, toggle to the Advanced View with `<t>`.

### Options controlling Ceres configuration

1. `LAPACK [Default: ON]`: By default Ceres will use `LAPACK` (& `BLAS`) if they are found. Turn this `OFF` to build Ceres without `LAPACK`. Turning this `OFF` also disables `SUITESPARSE` as it depends on `LAPACK`.

2. `SUITESPARSE [Default: ON]`: By default, Ceres will link to `SuiteSparse` if it and all of its dependencies are present. Turn this `OFF` to build Ceres without `SuiteSparse`. Note that `LAPACK` must be `ON` in order to build with `SuiteSparse`.

3. `CXSPARSE [Default: ON]`: By default, Ceres will link to `CXSparse` if all its dependencies are present. Turn this `OFF` to build Ceres without `CXSparse`.

4. `EIGENSPARSE [Default: OFF]`: By default, Ceres will not use Eigen’s sparse Cholesky factorization. The is because this part of the code is licensed under the `LGPL` and since `Eigen` is a header only library, including this code will result in an `LGPL` licensed version of Ceres.

   Note

   For good performance, use Eigen version 3.2.2 or later.

5. `GFLAGS [Default: ON]`: Turn this `OFF` to build Ceres without `gflags`. This will also prevent some of the example code from building.

6. `MINIGLOG [Default: OFF]`: Ceres includes a stripped-down, minimal implementation of `glog` which can optionally be used as a substitute for `glog`, thus removing `glog` as a required dependency. Turn this `ON` to use this minimal `glog` implementation.

7. `SCHUR_SPECIALIZATIONS [Default: ON]`: If you are concerned about binary size/compilation time over some small (10-20%) performance gains in the `SPARSE_SCHUR` solver, you can disable some of the template specializations by turning this `OFF`.

8. `OPENMP [Default: ON]`: On certain platforms like Android, multi-threading with `OpenMP` is not supported. Turn this `OFF` to disable multi-threading.

9. `CXX11 [Default: OFF]` Non-Windows platforms only.

   Although Ceres does not currently use C++11, it does use `shared_ptr` (required) and `unordered_map` (if available); both of which existed in the previous iterations of what became the C++11 standard: TR1 & C++0x. As such, Ceres can compile on pre-C++11 compilers, using the TR1/C++0x versions of `shared_ptr` & `unordered_map`.

   Note that on Linux (GCC & Clang), compiling against the TR1/C++0x versions: `CXX11=OFF` (the default) does not require `-std=c++11` when compiling Ceres, nor does it require that any client code using Ceres use `-std=c++11`. However, this will cause compile errors if any client code that uses Ceres also uses C++11 (mismatched versions of `shared_ptr` & `unordered_map`).

   Enabling this option: `CXX11=ON` forces Ceres to use the C++11 versions of `shared_ptr` & `unordered_map` if they are available, and thus imposes the requirement that all client code using Ceres also compile with `-std=c++11`. This requirement is handled automatically through CMake target properties on the exported Ceres target for CMake >= 2.8.12 (when it was introduced). Thus, any client code which uses CMake will automatically be compiled with `-std=c++11`. On CMake versions < 2.8.12, you are responsible for ensuring that any code which uses Ceres is compiled with `-std=c++11`.

   On OS X 10.9+, Clang will use the C++11 versions of `shared_ptr` & `unordered_map` without `-std=c++11` and so this option does not change the versions detected, although enabling it will require that client code compile with `-std=c++11`.

   The following table summarises the effects of the `CXX11` option:

   OS | CXX11 | Detected Version | Ceres & client code require `-std=c++11`
   --- | --- | --- | ---
   Linux (GCC & Clang) | OFF | tr1 | No
   Linux (GCC & Clang) | ON | std | Yes
   OS X 10.9+ | OFF | std | No
   OS X 10.9+ | ON | std | Yes

   The `CXX11` option does does not exist for Windows, as there any new C++ features available are enabled by default, and there is no analogue of `-std=c++11`.

10. `BUILD_SHARED_LIBS [Default: OFF]`: By default Ceres is built as a static library, turn this `ON` to instead build Ceres as a shared library.

11. `EXPORT_BUILD_DIR [Default: OFF]`: By default Ceres is configured solely for installation, and so must be installed in order for clients to use it. Turn this `ON` to export Ceres’ build directory location into the user’s local CMake package registry where it will be detected without requiring installation in a client project using CMake when find_package(Ceres) is invoked.

12. `BUILD_DOCUMENTATION [Default: OFF]`: Use this to enable building the documentation, requires Sphinx and the sphinx_rtd_theme package available from the Python package index. In addition, `make ceres_docs` can be used to build only the documentation.

13. `MSVC_USE_STATIC_CRT [Default: OFF]` Windows Only: By default Ceres will use the Visual Studio default, shared C-Run Time (CRT) library. Turn this `ON` to use the static C-Run Time library instead.

### Options controlling Ceres dependency locations

Ceres uses the `CMake` find_package function to find all of its dependencies using `Find<DEPENDENCY_NAME>.cmake` scripts which are either included in Ceres (for most dependencies) or are shipped as standard with `CMake` (for `LAPACK` & `BLAS`). These scripts will search all of the “standard” install locations for various OSs for each dependency. However, particularly for Windows, they may fail to find the library, in this case you will have to manually specify its installed location. The `Find<DEPENDENCY_NAME>.cmake` scripts shipped with Ceres support two ways for you to do this:

1. Set the hints variables specifying the directories to search in preference, but in addition, to the search directories in the `Find<DEPENDENCY_NAME>.cmake` script:

   - `<DEPENDENCY_NAME (CAPS)>_INCLUDE_DIR_HINTS`
   - `<DEPENDENCY_NAME (CAPS)>_LIBRARY_DIR_HINTS`

   These variables should be set via `-D<VAR>=<VALUE>` `CMake` arguments as they are not visible in the GUI.

2. Set the variables specifying the explicit include directory and library file to use:

   - `<DEPENDENCY_NAME (CAPS)>_INCLUDE_DIR`
   - `<DEPENDENCY_NAME (CAPS)>_LIBRARY`

   This bypasses all searching in the `Find<DEPENDENCY_NAME>.cmake` script, but validation is still performed.

   These variables are available to set in the `CMake` GUI. They are visible in the Standard View if the library has not been found (but the current Ceres configuration requires it), but are always visible in the Advanced View. They can also be set directly via `-D<VAR>=<VALUE>` arguments to `CMake`.

### Building using custom BLAS & LAPACK installs

If the standard find package scripts for `BLAS` & `LAPACK` which ship with `CMake` fail to find the desired libraries on your system, try setting `CMAKE_LIBRARY_PATH` to the path(s) to the directories containing the `BLAS` & `LAPACK` libraries when invoking `CMake` to build Ceres via `-D<VAR>=<VALUE>`. This should result in the libraries being found for any common variant of each.

If you are building on an exotic system, or setting `CMAKE_LIBRARY_PATH` does not work, or is not appropriate for some other reason, one option would be to write your own custom versions of `FindBLAS.cmake` & `FindLAPACK.cmake` specific to your environment. In this case you must set `CMAKE_MODULE_PATH` to the directory containing these custom scripts when invoking `CMake` to build Ceres and they will be used in preference to the default versions. However, in order for this to work, your scripts must provide the full set of variables provided by the default scripts. Also, if you are building Ceres with `SuiteSparse`, the versions of `BLAS` & `LAPACK` used by `SuiteSparse` and Ceres should be the same.

## Using Ceres with CMake

In order to use Ceres in client code with CMake using find_package() then either:

1. Ceres must have been installed with `make install`.

     If the install location is non-standard (i.e. is not in CMake’s default search paths) then it will not be detected by default, see: Local installations.

     Note that if you are using a non-standard install location you should consider exporting Ceres instead, as this will not require any extra information to be provided in client code for Ceres to be detected.

2. Or Ceres’ build directory must have been exported

     by enabling the `EXPORT_BUILD_DIR` option when Ceres was configured.

As an example of how to use Ceres, to compile examples/helloworld.cc in a separate standalone project, the following CMakeList.txt can be used:

    cmake_minimum_required(VERSION 2.8)

    project(helloworld)

    find_package(Ceres REQUIRED)
    include_directories(${CERES_INCLUDE_DIRS})

    # helloworld
    add_executable(helloworld helloworld.cc)
    target_link_libraries(helloworld ${CERES_LIBRARIES})

Irrespective of whether Ceres was installed or exported, if multiple versions are detected, set: `Ceres_DIR` to control which is used. If Ceres was installed `Ceres_DIR` should be the path to the directory containing the installed `CeresConfig.cmake` file (e.g. `/usr/local/share/Ceres`). If Ceres was exported, then `Ceres_DIR` should be the path to the exported Ceres build directory.

### Specify Ceres version

Additionally, when CMake has found Ceres it can optionally check the package version, if it has been specified in the find_package() call. For example:

    find_package(Ceres 1.2.3 REQUIRED)

### Local installations

If Ceres was installed in a non-standard path by specifying `-DCMAKE_INSTALL_PREFIX="/some/where/local"`, then the user should add the PATHS option to the `find_package()` command, e.g.,

    find_package(Ceres REQUIRED PATHS "/some/where/local/")

Note that this can be used to have multiple versions of Ceres installed. However, particularly if you have only a single version of Ceres which you want to use but do not wish to install to a system location, you should consider exporting Ceres using the `EXPORT_BUILD_DIR` option instead of a local install, as exported versions of Ceres will be automatically detected by CMake, irrespective of their location.

### Understanding the CMake Package System

Although a full tutorial on CMake is outside the scope of this guide, here we cover some of the most common CMake misunderstandings that crop up when using Ceres. For more detailed CMake usage, the following references are very useful:

- The official CMake tutorial

  > Provides a tour of the core features of CMake.

- ProjectConfig tutorial and the cmake-packages documentation

  > Cover how to write a `ProjectConfig.cmake` file, discussed below, for your own project when installing or exporting it using CMake. It also covers how these processes in conjunction with `find_package()` are actually handled by CMake. The ProjectConfig tutorial is the older style, currently used by Ceres for compatibility with older versions of CMake.

  Note

  Targets in CMake.

  All libraries and executables built using CMake are represented as targets created using add_library() and add_executable(). Targets encapsulate the rules and dependencies (which can be other targets) required to build or link against an object. This allows CMake to implicitly manage dependency chains. Thus it is sufficient to tell CMake that a library target: `B` depends on a previously declared library target `A`, and CMake will understand that this means that `B` also depends on all of the public dependencies of `A`.

When a project like Ceres is installed using CMake, or its build directory is exported into the local CMake package registry (see Installing a project with CMake vs Exporting its build directory), in addition to the public headers and compiled libraries, a set of CMake-specific project configuration files are also installed to: `<INSTALL_ROOT>/share/Ceres` (if Ceres is installed), or created in the build directory (if Ceres’ build directory is exported). When find_package is invoked, CMake checks various standard install locations (including `/usr/local` on Linux & UNIX systems), and the local CMake package registry for CMake configuration files for the project to be found (i.e. Ceres in the case of `find_package(Ceres)`). Specifically it looks for:

- `<PROJECT_NAME>Config.cmake` (or `<lower_case_project_name>-config.cmake`)

  > Which is written by the developers of the project, and is configured with the selected options and installed locations when the project is built and defines the CMake variables: `<PROJECT_NAME>_INCLUDE_DIRS` & `<PROJECT_NAME>_LIBRARIES` which are used by the caller to import the project.

The `<PROJECT_NAME>Config.cmake` typically includes a second file installed to the same location:

- `<PROJECT_NAME>Targets.cmake`

  > Which is autogenerated by CMake as part of the install process and defines imported targets for the project in the caller’s CMake scope.

An imported target contains the same information about a library as a CMake target that was declared locally in the current CMake project using `add_library()`. However, imported targets refer to objects that have already been built by a different CMake project. Principally, an imported target contains the location of the compiled object and all of its public dependencies required to link against it. Any locally declared target can depend on an imported target, and CMake will manage the dependency chain, just as if the imported target had been declared locally by the current project.

Crucially, just like any locally declared CMake target, an imported target is identified by its name when adding it as a dependency to another target.

Thus, if in a project using Ceres you had the following in your CMakeLists.txt:

    find_package(Ceres REQUIRED)
    message("CERES_LIBRARIES = ${CERES_LIBRARIES}")

You would see the output: `CERES_LIBRARIES = ceres`. However, here `ceres` is an imported target created when `CeresTargets.cmake` was read as part of `find_package(Ceres REQUIRED)`. It does not refer (directly) to the compiled Ceres library: `libceres.a/so/dylib/lib`. This distinction is important, as depending on the options selected when it was built, Ceres can have public link dependencies which are encapsulated in the imported target and automatically added to the link step when Ceres is added as a dependency of another target by CMake. In this case, linking only against `libceres.a/so/dylib/lib` without these other public dependencies would result in a linker error.

Note that this description applies both to projects that are installed using CMake, and to those whose build directory is exported using export() (instead of install()). Ceres supports both installation and export of its build directory if the `EXPORT_BUILD_DIR` option is enabled, see Customizing the build.

#### Installing a project with CMake vs Exporting its build directory

When a project is installed, the compiled libraries and headers are copied from the source & build directory to the install location, and it is these copied files that are used by any client code. When a project’s build directory is exported, instead of copying the compiled libraries and headers, CMake creates an entry for the project in the user’s local CMake package registry, `<USER_HOME>/.cmake/packages` on Linux & OS X, which contains the path to the project’s build directory which will be checked by CMake during a call to `find_package()`. The effect of which is that any client code uses the compiled libraries and headers in the build directory directly, thus not requiring the project to be installed to be used.

### Installing / Exporting a project that uses Ceres

As described in Understanding the CMake Package System, the contents of the `CERES_LIBRARIES` variable is the name of an imported target which represents Ceres. If you are installing / exporting your own project which uses Ceres, it is important to understand that:

imported targets are not (re)exported when a project which imported them is exported.

Thus, when a project `Foo` which uses Ceres is exported, its list of dependencies as seen by another project `Bar` which imports `Foo` via: `find_package(Foo REQUIRED)` will contain: `ceres`. However, the definition of `ceres` as an imported target is not (re)exported when Foo is exported. Hence, without any additional steps, when processing `Bar`, `ceres` will not be defined as an imported target. Thus, when processing `Bar`, CMake will assume that `ceres` refers only to: `libceres.a/so/dylib/lib` (the compiled Ceres library) directly if it is on the current list of search paths. In which case, no CMake errors will occur, but `Bar` will not link properly, as it does not have the required public link dependencies of Ceres, which are stored in the imported target defintion.

The solution to this is for `Foo` (i.e., the project that uses Ceres) to invoke `find_package(Ceres)` in `FooConfig.cmake`, thus `ceres` will be defined as an imported target when CMake processes `Bar`. An example of the required modifications to `FooConfig.cmake` are show below:

    # Importing Ceres in FooConfig.cmake using CMake 2.8.x style.
    #
    # When configure_file() is used to generate FooConfig.cmake from
    # FooConfig.cmake.in, @Ceres_DIR@ will be replaced with the current
    # value of Ceres_DIR being used by Foo.  This should be passed as a hint
    # when invoking find_package(Ceres) to ensure that the same install of
    # Ceres is used as was used to build Foo.
    set(CERES_DIR_HINTS @Ceres_DIR@)

    # Forward the QUIET / REQUIRED options.
    if (Foo_FIND_QUIETLY)
       find_package(Ceres QUIET HINTS ${CERES_DIR_HINTS})
    elseif (Foo_FIND_REQUIRED)
       find_package(Ceres REQUIRED HINTS ${CERES_DIR_HINTS})
    else ()
       find_package(Ceres HINTS ${CERES_DIR_HINTS})
    endif()

    # Importing Ceres in FooConfig.cmake using CMake 3.x style.
    #
    # In CMake v3.x, the find_dependency() macro exists to forward the REQUIRED
    # / QUIET parameters to find_package() when searching for dependencies.
    #
    # Note that find_dependency() does not take a path hint, so if Ceres was
    # installed in a non-standard location, that location must be added to
    # CMake's search list before this call.
    include(CMakeFindDependencyMacro)
    find_dependency(Ceres)