Integrating Modular SLAM Pipeline into OpenCV Contrib

[QueenofUSSR]

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

Summary

This PR adds the SLAM module (slam) providing a compact visual odometry and small-scale SLAM toolkit. The module includes feature extraction, matching, two-view initialization, pose estimation, local mapping (MapManager / MapPoint), a simple optimizer (local BA with SFM fallback and optional g2o support), visualizer/top-down trajectory, localizer (PnP-based relocalization), and utilities for loading image sequences and intrinsics.

Motivation

Offer a lightweight, self-contained SLAM implementation that demonstrates how to use OpenCV building blocks for VO/SLAM research and examples. Useful as an educational reference and quick prototyping base for researchers who want to extend or compare with other methods (ORB-SLAM family, etc.). It also provides a straightforward path to enable g2o when available for robust BA.

What changed / what’s included

slam.hpp — module aggregator
vo.hpp — VisualOdometry wrapper
data_loader.hpp — sequence loader with YAML intrinsics parsing
feature.hpp — FeatureExtractor (ORB + ANMS + flow-aware selection)
matcher.hpp — Matcher (ratio test, bucketing, mutual check)
initializer.hpp — Two-view initializer using H/F decomposition + triagulation
pose.hpp — PoseEstimator (essential matrix + recoverPose)
map.hpp & keyframe.hpp — MapManager, MapPoint, KeyFrame
localizer.hpp — PnP-based relocalizer
optimizer.hpp — Optimizer (local BA using either g2o or OpenCV-based SFM fallback)
visualizer.hpp — simple frame/top-down visualization and trajectory saving
Implementation (under src/):
vo.cpp — main VisualOdometry run loop, backend thread for local BA, CSV diagnostics, initialization + tracking + triangulation pipeline
data_loader.cpp — filesystem/glob image enumerator, optional sensor.yaml intrinsics parsing (small comment fix in this PR)
feature.cpp, matcher.cpp, initializer.cpp, pose.cpp, optimizer.cpp, visualizer.cpp, localizer.cpp — corresponding implementations described above

[abhishek-gola]

FAILED: modules/slam/CMakeFiles/opencv_slam.dir/src/data_loader.cpp.o 
/usr/bin/ccache /usr/bin/c++  -DCVAPI_EXPORTS -D_USE_MATH_DEFINES -D__OPENCV_BUILD=1 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/ci/opencv/hal/ipp/include -I3rdparty/ippicv/ippicv_lnx/icv/include -I3rdparty/ippicv/ippicv_lnx/iw/include -I/home/ci/opencv/3rdparty/dlpack/include -I/home/ci/opencv_contrib/modules/slam/include -Imodules/slam -I/home/ci/opencv_contrib/modules/cudev/include -I/home/ci/opencv/modules/core/include -I/home/ci/opencv_contrib/modules/cudaarithm/include -I/home/ci/opencv/modules/flann/include -I/home/ci/opencv/modules/imgproc/include -I/home/ci/opencv/modules/ml/include -I/home/ci/opencv/modules/dnn/include -I/home/ci/opencv/modules/features2d/include -I/home/ci/opencv/modules/imgcodecs/include -I/home/ci/opencv/modules/videoio/include -I/home/ci/opencv/modules/calib3d/include -I/home/ci/opencv/modules/highgui/include -I/home/ci/opencv_contrib/modules/shape/include -I/home/ci/opencv/modules/video/include -I/home/ci/opencv_contrib/modules/xfeatures2d/include -I/home/ci/opencv_contrib/modules/sfm/include -isystem . -isystem /usr/include/eigen3 -fsigned-char -W -Wall -Wreturn-type -Wnon-virtual-dtor -Waddress -Wsequence-point -Wformat -Wformat-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections  -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG  -DNDEBUG -fPIC   -std=c++17 -MD -MT modules/slam/CMakeFiles/opencv_slam.dir/src/data_loader.cpp.o -MF modules/slam/CMakeFiles/opencv_slam.dir/src/data_loader.cpp.o.d -o modules/slam/CMakeFiles/opencv_slam.dir/src/data_loader.cpp.o -c /home/ci/opencv_contrib/modules/slam/src/data_loader.cpp
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:7:6: error: invalid preprocessing directive #namespace
    7 | #    namespace fs = std::filesystem;
      |      ^~~~~~~~~
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp: In constructor 'cv::vo::DataLoader::DataLoader(const string&)':
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:33:9: error: 'fs' has not been declared
   33 |         fs::path p(imageDir);
      |         ^~
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:34:13: error: 'fs' has not been declared
   34 |         if(!fs::exists(p) || !fs::is_directory(p)){
      |             ^~
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:34:24: error: 'p' was not declared in this scope
   34 |         if(!fs::exists(p) || !fs::is_directory(p)){
      |                        ^
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:34:31: error: 'fs' has not been declared
   34 |         if(!fs::exists(p) || !fs::is_directory(p)){
      |                               ^~
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:67:5: error: 'fs' has not been declared
   67 |     fs::path p(imageDir);
      |     ^~
/home/ci/opencv_contrib/modules/slam/src/data_loader.cpp:68:26: error: 'p' was not declared in this scope
   68 |     std::string yaml1 = (p / "sensor.yaml").string();
      |                          ^
[2987/3796] Building CXX object modules/sfm/src/libmv/libmv/correspondence/CMakeFiles/opencv.sfm.correspondence.dir/nRobustViewMatching.cc.o
[2988/3796] Building CXX object modules/slam/CMakeFiles/opencv_slam.dir/src/matcher.cpp.o
/home/ci/opencv_contrib/modules/slam/src/matcher.cpp: In member function 'void cv::vo::Matcher::match(const cv::Mat&, const cv::Mat&, const std::vector<cv::KeyPoint>&, const std::vector<cv::KeyPoint>&, std::vector<cv::DMatch>&, int, int, int, int, int, int, bool, bool)':
/home/ci/opencv_contrib/modules/slam/src/matcher.cpp:26:50: warning: unused parameter 'kps1' [-Wunused-parameter]
   26 |                     const std::vector<KeyPoint> &kps1, const std::vector<KeyPoint> &kps2,
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
[2989/3796] Building CXX object modules/slam/CMakeFiles/opencv_slam.dir/src/feature.cpp.o
/home/ci/opencv_contrib/modules/slam/src/feature.cpp: In lambda function:
/home/ci/opencv_contrib/modules/slam/src/feature.cpp:142:80: warning: declaration of 'b' shadows a previous local [-Wshadow]
  142 |         std::sort(b.begin(), b.end(), [](const CandScore &a, const CandScore &b){ return a.score > b.score; });
      |                                                                                ^
/home/ci/opencv_contrib/modules/slam/src/feature.cpp:140:15: note: shadowed declaration is here
  140 |     for(auto &b: buckets){
      |               ^
[2990/3796] Building CXX object modules/slam/CMakeFiles/opencv_slam.dir/src/localizer.cpp.o
[2991/3796] Building CXX object modules/slam/CMakeFiles/opencv_slam.dir/src/map.cpp.o
[2992/3796] Building CXX object modules/slam/CMakeFiles/opencv_slam.dir/src/initializer.cpp.o
/home/ci/opencv_contrib/modules/slam/src/initializer.cpp: In member function 'void cv::vo::Initializer::decomposeH(const cv::Mat&, std::vector<cv::Mat>&, std::vector<cv::Mat>&, std::vector<cv::Mat>&)':
/home/ci/opencv_contrib/modules/slam/src/initializer.cpp:318:9: warning: unused variable 'solutions' [-Wunused-variable]
  318 |     int solutions = decomposeHomographyMat(H_normalized, Mat::eye(3,3,CV_64F),
      |         ^~~~~~~~~

@QueenofUSSR build is failing.