Extract eigenvalue-based features from point cloud segments
Eigenvalue-based features characterize geometrical features of point cloud segments. These features can be used in simultaneous localization and mapping (SLAM) applications for loop closure detection and localization in a target map.
[___] = extractEigenFeatures(___,NormalizeEigenvalues=tf)
normalizes the eigenvalues prior to computing features, specified as
true when the next step is to use a classifier to assign a semantic
label to a 3-D point. Set
false when the next
step is to find matching features. The default value is
Load an organized lidar point cloud.
ld = load('drivingLidarPoints.mat'); ptCloud = ld.ptCloud;
Segment and remove the ground plane.
groundPtsIdx = segmentGroundFromLidarData(ptCloud,'ElevationAngleDelta',15); ptCloud = select(ptCloud,~groundPtsIdx,'OutputSize','full');
Cluster the remaining points with a minimum of 50 points per cluster.
distThreshold = 0.5; % in meters minPoints = 50; [labels,numClusters] = segmentLidarData(ptCloud,distThreshold,'NumClusterPoints',minPoints);
Compute eigenvalue-based features.
features = extractEigenFeatures(ptCloud,labels,'NormalizeEigenvalues',true)
features=17×1 object 16x1 eigenFeature array with properties: Feature Centroid ⋮
Create a Velodyne PCAP file reader.
veloReader = velodyneFileReader('lidarData_ConstructionRoad.pcap','HDL32E');
Read the first and fourth scans from the file.
ptCloud1 = readFrame(veloReader,1); ptCloud2 = readFrame(veloReader,4);
Remove the ground plane from the scans.
maxDistance = 1; % in meters referenceVector = [0 0 1]; [~,~,selectIdx] = pcfitplane(ptCloud1,maxDistance,referenceVector); ptCloud1 = select(ptCloud1,selectIdx,'OutputSize','full'); [~,~,selectIdx] = pcfitplane(ptCloud2,maxDistance,referenceVector); ptCloud2 = select(ptCloud2,selectIdx,'OutputSize','full');
Cluster the point clouds with a minimum of 10 points per cluster.
minDistance = 2; % in meters minPoints = 10; labels1 = pcsegdist(ptCloud1,minDistance,'NumClusterPoints',minPoints); labels2 = pcsegdist(ptCloud2,minDistance,'NumClusterPoints',minPoints);
Extract eigen-value features and the corresponding segments from each point cloud.
[eigFeatures1,segments1] = extractEigenFeatures(ptCloud1,labels1); [eigFeatures2,segments2] = extractEigenFeatures(ptCloud2,labels2);
Create matrices of the features and centroids extracted from each point cloud, for matching.
features1 = vertcat(eigFeatures1.Feature); features2 = vertcat(eigFeatures2.Feature); centroids1 = vertcat(eigFeatures1.Centroid); centroids2 = vertcat(eigFeatures2.Centroid);
Find putative feature matches.
indexPairs = pcmatchfeatures(features1,features2, ... pointCloud(centroids1),pointCloud(centroids2));
Get the matched segments and features for visualization.
matchedSegments1 = segments1(indexPairs(:,1)); matchedSegments2 = segments2(indexPairs(:,2)); matchedFeatures1 = eigFeatures1(indexPairs(:,1)); matchedFeatures2 = eigFeatures2(indexPairs(:,2));
Visualize the matches.
figure pcshowMatchedFeatures(matchedSegments1,matchedSegments2,matchedFeatures1,matchedFeatures2) title('Matched Segments')
labels— Cluster labels
Cluster labels, specified as an M-element vector of numeric
values for unorganized point clouds or an M-by-N
matrix of numeric values for organized point clouds. The labels correspond to the
results of segmenting the input point cloud. Each point in the point cloud has a cluster
label, specified by the corresponding element in
segmentsIn— Point cloud segments
Point cloud segments, specified as a vector of
pointCloud objects. Each point cloud segment in the input must have a
minimum of two points for feature extraction. No features or segments are returned for
input segments with only one point.
features— Eigenvalue-based features
Eigenvalue-based features, returned as a vector of
objects. When you extract features from a labeled point cloud input, each element in
this vector contains the features extracted from the corresponding cluster of labeled
points. When you extract features from a segments input, each element in this vector
contains the features extracted from the corresponding element in the segments
segmentsOut— Segments extracted from point cloud
Segments extracted from the point cloud, specified as a vector of
pointCloud objects. The length of the segments vector corresponds to the
number of nonzero, unique labels.
 Weinmann, M., B. Jutzi, and C. Mallet. “Semantic 3D Scene Interpretation: A Framework Combining Optimal Neighborhood Size Selection with Relevant Features.” ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences II–3 (August 7, 2014): 181–88. https://doi.org/10.5194/isprsannals-II-3-181-2014.