How to extract individual tree pointcloud to las/laz file?

Hi,

I've followed the instruction at Extract Forest Metrics and Individual Tree Attributes from Aerial Lidar Data - MATLAB & Simulink - MathWorks Australia and got the results of "TreeId"

From here, I wonder how to get these 5 trees into 5 different las/laz files?

Base on LAS or LAZ file writer - MATLAB - MathWorks Australia, I tried "lasWriter = lasFileWriter(TreeId1)" but it says "Unrecognized function or variable 'TreeId'.

Thanks in advance,

Answer 1

[Pratyush Swain]

Hi Ha Ninh,

I understand you want to convert individual tree points into point clouds and save them into laz files. For this purpose we have to utilize the 'normalizedPoints' and 'label3D' variables.

Please follow the implementation below after you have realised the tree metrics with reference to the example in https://www.mathworks.com/help/lidar/ug/extraction-of-forest-metrics-and-individual-tree-attributes.html#ExtractionOfForestAndIndividualTreeMetricsExample-8 :

% Consider points belongs to valid labels

validLabels = label3D ~= 0;

filteredLabels = label3D(validLabels);

filteredPoints = normalizedPoints(validLabels,:);

[filteredLabels, sortedIds] = sort(filteredLabels);

filteredPoints = filteredPoints(sortedIds,:);

The above data processing is similar to that performed 'helperExtractTreeMetrics' function. However instead of performing tree metrics analysis, we can proceed towards grouping points as per corresponding labels.

% Find groups based on filteredLabel

groups = findgroups(filteredLabel);

% Split the filteredPoints array based on the groups and apply a function to each group

groupedData =(@(x) {x}, filteredPoints, groups);

Finally we can iterate over grouped data to convert the points into point cloud and finally write them to laz files.

for i = 1:numel(groupedData)
    
    points = groupedData{i};  % Access the points for a specific group
    
    ptCloud = pointCloud(points);  % Convert the points into a pointCloud
    
    filename = sprintf('group_%d.laz', i);  % Generate a filename for the LAS file
    
    lasWriter = lasFileWriter(filename);
    
    writePointCloud(lasWriter,ptCloud);
    
end

For more information please refer to:

• https://www.mathworks.com/help/lidar/ref/lasfilewriter.html
• https://www.mathworks.com/help/matlab/ref/splitapply.html
• https://www.mathworks.com/help/vision/ref/pointcloud.html

Hope this helps.