Ceres 2.0.0 upgrade to C++14 breaks sfm module

[ghfue]

System information (version)

• OpenCV => master
• Operating System / Platform => Ubuntu 18.04
• Compiler => g++ 7.5.0

Detailed description

The sfm module does not build with Ceres master (2.0.0) due to Ceres switching to C++14.

When building OpenCV, it throws an error about integer_sequence not being a member of std. This is due to integer_sequence being added in C++14.

I was able to build OpenCV with Ceres 2.0.0 by building it with C++14, but I am not confident this is the proper solution for everyone.

The alternative solution would be to stay on Ceres 1.X.X, which could just be documented somewhere.

Steps to reproduce

• Build ceres from master (2.0.0 has yet to be tagged)
• Build OpenCV with modules

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc

[NavneetSajwan]

Yes, finally someone addressed it. It was driving me mad for months. Is there a workaround until it gets fixed?

[alalek]

There is no other way than forcing C++14 compilation mode to compile with new Ceres:

• modern CMake (3.1+) + cmake -DCMAKE_CXX_STANDARD=14 ...
• or update CXXFLAGS / CMAKE_CXX_FLAGS / OPENCV_EXTRA_CXX_FLAGS to use C++14

Otherwise we should disable Ceres in OpenCV:

• cmake -DCMAKE_DISABLE_FIND_PACKAGE_Ceres=ON ...
• automatic detection of broken compilation can be added later (or just Ceres version check)

[NavneetSajwan]

If I use an older version of ceres, will SFM work? I am hoping the 1.14.0 version doesn't have this issue. @alalek

[ghfue]

@NavneetSajwan I tested yesterday, and everything builds fine with Ceres 1.14.0. The C++14 change was not introduced until 2.0.0.

[NavneetSajwan]

Thanks, I confirmed it. No installation errors with ceres 1.4.x . But SFM examples are not built even when -D BUILD_EXAMPLES=ON. Did you face the same issue? @alalek

[diablodale]

FYI, if SFM cmake is updated to c++14, keep in mind that it currently fails its intention on Microsoft compilers. This is due to this following hardcoded option.

opencv_contrib/modules/sfm/CMakeLists.txt

Line 71 in bdc0101

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

If continuing with the hardcoded approach....Microsoft's cl.exe compiler does not support that option in that specific format. You can use a - or /. You can not use an equal sign = to separate the option and its value. Microsoft's compiler wants a colon :. Also keep in mind that starting with Microsoft VS2017, the default is C++14.

[NikolausDemmel]

On macOS, this prevents the ceres-solver formula in Homebrew to be updated to Ceres 2.0.0, since it breaks the opencv formula.

Same issue will be with the rgbd module, which recently acquired a dependency on ceres: #2619

[wzh4464]

If I use an older version of ceres, will SFM work? I am hoping the 1.14.0 version doesn't have this issue. @alalek

How to use old version?