How to get covariance matrix from point cloud data using PCL library?

Question

I want a sample code that can get covariance matrix from point cloud data using PCL.

I looked at the PCL documentation and I found this code to calculate covariance:

// Placeholder for the 3x3 covariance matrix at each surface patch
Eigen::Matrix3f covariance_matrix;

// 16-bytes aligned placeholder for the XYZ centroid of a surface patch
Eigen::Vector4f xyz_centroid;

// Estimate the XYZ centroid
compute3DCentroid (cloud, xyz_centroid);

// Compute the 3x3 covariance matrix
computeCovarianceMatrix (cloud, xyz_centroid, covariance_matrix); 

Answer 1

That is straight forward, but I guess you need more reading the documentations/tutorials :)

1- load the PCD file, for example:

pcl::PointCloud<pcl::PointXYZ>::Ptr cloud (new pcl::PointCloud<pcl::PointXYZ> ());
pcl::io::loadPCDFile("c:\path\pcdfile.pcd",*cloud)

2- calculate the centroid:

Eigen::Vector4f xyz_centroid;
compute3DCentroid (cloud, xyz_centroid);

3- calculate the covariance

Eigen::Matrix3f covariance_matrix;
computeCovarianceMatrix (cloud, xyz_centroid, covariance_matrix);