Move further towards KdTreeNanoflann Part A

[mvieth]

Preparation for #6468

• Add include for pcl/search/kdtree.h where it is used, previously those files relied on transitive includes. This makes it easier to remove includes in other files.
• Add the kdtree module as an explicit dependency for those test modules that use it. This makes it easier to remove dependencies on the kdtree module in other modules (e.g. filters, features, segmentation, ...).
• In extract_clusters, two extractEuclideanClusters functions use pcl::KdTree. These are now only available if the FLANN library has been found (and thus, the kdtree module is built). Additionally, I added overloads to these two functions which use the generic pcl::search::Search instead of pcl::KdTree.

[Copilot]

Pull request overview

Prepares the codebase for the ongoing move toward KdTreeNanoflann by reducing reliance on transitive includes, making kdtree dependencies explicit in tests, and introducing pcl::search::Search-based overloads in cluster extraction to decouple callers from pcl::KdTree.

Changes:

• Add missing direct includes (notably pcl/search/kdtree.h / pcl/search/auto.h) in tests, examples, apps, and tutorials that previously relied on transitive headers.
• Make kdtree an explicit dependency for multiple test subsystems that use it.
• Update extract_clusters.h to (a) gate pcl::KdTree overloads behind PCL_HAS_FLANN and (b) add pcl::search::Search overloads for normal-aware Euclidean clustering.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tools/sac_segmentation_plane.cpp	Adds a direct point types include to avoid transitive dependency.
test/visualization/CMakeLists.txt	Adds kdtree as an explicit test dependency.
test/surface/CMakeLists.txt	Adds kdtree as an explicit test dependency.
test/search/CMakeLists.txt	Adds kdtree as an explicit test dependency.
test/registration/test_sac_ia.cpp	Adds direct pcl/search/kdtree.h include where used.
test/registration/test_registration.cpp	Adds direct pcl/search/kdtree.h include where used.
test/registration/test_registration_api.cpp	Adds direct pcl/search/kdtree.h include where used.
test/registration/test_ndt.cpp	Adds direct pcl/search/kdtree.h include where used.
test/registration/test_correspondence_estimation.cpp	Adds direct pcl/search/kdtree.h include where used.
test/registration/CMakeLists.txt	Makes io and kdtree explicit dependencies for registration tests.
test/recognition/CMakeLists.txt	Adds kdtree as an explicit test dependency.
test/keypoints/CMakeLists.txt	Adds kdtree as an explicit test dependency.
test/filters/CMakeLists.txt	Adds kdtree as an explicit test dependency.
test/features/CMakeLists.txt	Adds kdtree as an explicit test dependency.
segmentation/include/pcl/segmentation/extract_clusters.h	Gates pcl::KdTree overloads on PCL_HAS_FLANN and adds pcl::search::Search overloads for normal-aware clustering.
registration/src/gicp6d.cpp	Makes search backend selection explicit and adjusts tree construction for nanoflann/FLANN.
registration/include/pcl/registration/gicp6d.h	Generalizes member type from KdTree to Search to support multiple backends.
examples/segmentation/example_extract_clusters_normals.cpp	Switches example to pcl::search::autoSelectMethod for backend-agnostic search selection.
examples/features/example_difference_of_normals.cpp	Adds direct pcl/search/kdtree.h include where used.
doc/tutorials/content/sources/template_alignment/template_alignment.cpp	Replaces direct FLANN kdtree include with pcl/search/kdtree.h.
doc/tutorials/content/sources/rops_feature/rops_feature.cpp	Adds direct pcl/search/kdtree.h include where used.
doc/tutorials/content/sources/pcl_visualizer/pcl_visualizer_demo.cpp	Adds direct pcl/search/kdtree.h include where used.
doc/tutorials/content/sources/pairwise_incremental_registration/pairwise_incremental_registration.cpp	Adds direct pcl/search/kdtree.h include where used.
doc/tutorials/content/sources/cylinder_segmentation/cylinder_segmentation.cpp	Adds direct pcl/search/kdtree.h include where used.
doc/tutorials/content/sources/correspondence_grouping/correspondence_grouping.cpp	Adds direct pcl/search/kdtree.h include where used.
doc/tutorials/content/sources/conditional_euclidean_clustering/conditional_euclidean_clustering.cpp	Adds direct pcl/search/kdtree.h include where used.
apps/src/ppf_object_recognition.cpp	Adds direct pcl/search/kdtree.h include where used.
apps/src/pcd_select_object_plane.cpp	Adds direct pcl/search/kdtree.h include where used.
apps/src/openni_tracking.cpp	Adds direct pcl/search/kdtree.h include where used.

Suppressed comments (1)

registration/src/gicp6d.cpp:100

• Same exception-safety issue as in the nanoflann branch: using raw new + reset can leak if an intermediate call throws. Construct the shared_ptr first and then assign to the Search base pointer.

  auto tree = new pcl::search::KdTree<pcl::PointXYZLAB>(false);
  tree->setPointRepresentation(pcl::make_shared<MyPointRepresentation>(point_rep_));
  tree->setInputCloud(target_lab_);
  target_tree_lab_.reset(tree);

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