Intrinsic shape signatures (ISS) 固有形状特征码
在本教程中，我们将展示如何检测 3D 形状的 ISS 关键点。该实现基于于忠提出的关键点检测模块，“内在形状特征：用于3D对象识别的形状描述符”，2009年。（ Yu Zhong , “Intrinsic Shape Signatures: A Shape Descriptor for 3D Object Recognition）
ISS Keypoints
ISS 显著性测度基于属于p pp的点的散射矩Σ(p)的特征值分解（EVD）。
Σ(p)=N1q∈N(p)∑(q−μp)(q−μp)Twithμp=N1q∈N(p)∑q
给定Σ(p)，其数量级数量级递减的特征值在这里表示为 λ1、λ2、λ3。在修剪阶段，保留两个连续特征值之间比率低于阈值的点：
λ1(p)λ2(p)<γ12∧λ2(p)λ3(p)<γ23
其基本原理是避免在沿主要方向表现出类似扩散的点上检测关键点，在这些点上无法建立可重复的规范参考系，因此，随后的描述阶段很难变得有效。在其余点中，显著性由最小特征值的大小决定
ρ(p)≐λ3(p)
以便仅包括沿每个主方向变化较大的点。
在检测步骤之后，如果某个点在给定邻域上具有最大显著性值，则该点将被视为关键点。
注意：有关更多详细信息，请参考原始出版物或Tombari et.al 的“3D关键点探测器的性能评估”(Performance Evaluation of 3D Keypoint Detectors)。
ISS keypoint detection example ISS 关键点检测示例
#Intrinsic shape siqnatures import open3d as o3d import time # Compute ISS Keypoints on ArmadilloMesh armadillo_path = r'../data/ArmadilloMesh.ply' mesh = o3d.io.read_triangle_mesh(armadillo_path) mesh.compute_vertex_normals() pcd = o3d.geometry.PointCloud() pcd.points = mesh.vertices tic = time.time() keypoints = o3d.geometry.keypoint.compute_iss_keypoints(pcd) toc = 1000 * (time.time() - tic) print("ISS Computation took {:.0f} [ms]".format(toc)) mesh.compute_vertex_normals() mesh.paint_uniform_color([0.5, 0.5, 0.5]) keypoints.paint_uniform_color([1.0, 0.75, 0.0]) o3d.visualization.draw_geometries([keypoints, mesh])
# This function is only used to make the keypoints look better on the rendering def keypoints_to_spheres(keypoints): spheres = o3d.geometry.TriangleMesh() for keypoint in keypoints.points: sphere = o3d.geometry.TriangleMesh.create_sphere(radius=0.001) sphere.translate(keypoint) spheres += sphere spheres.paint_uniform_color([1.0, 0.75, 0.0]) return spheres # Compute ISS Keypoints on Standford BunnyMesh, changing the default parameters bunny_path = r'../data/BunnyMesh.ply' mesh = o3d.io.read_triangle_mesh(bunny_path) mesh.compute_vertex_normals() pcd = o3d.geometry.PointCloud() pcd.points = mesh.vertices tic = time.time() keypoints = o3d.geometry.keypoint.compute_iss_keypoints(pcd, salient_radius=0.005, non_max_radius=0.005, gamma_21=0.5, gamma_32=0.5) toc = 1000 * (time.time() - tic) print("ISS Computation took {:.0f} [ms]".format(toc)) mesh.compute_vertex_normals() mesh.paint_uniform_color([0.5, 0.5, 0.5]) o3d.visualization.draw_geometries([keypoints_to_spheres(keypoints), mesh])
