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hasFrame

Determine if another Ouster point cloud is available in the ROS messages

Since R2024a

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Syntax

isAvailable = hasFrame(ousterReader)

Description

isAvailable = hasFrame(ousterReader) determines if another point cloud is available in the Ouster® ROS messages.

example

Examples

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Open Live Script

This example shows how to handle Ouster ROS messages from an Ouster® lidar sensor to visualize point cloud data from road intersection.

Ouster ROS messages store data in a format that requires some interpretation before it can be used for further processing. MATLAB® can help you by formatting Ouster ROS messages for easy use.

Download lidar capture data of road intersection from MathWorks® Supportfiles site.

httpsUrl = "https://ssd.mathworks.com";
dataUrl = strcat(httpsUrl,"/supportfiles/spc/ROS/ROS_Ouster_Supportfiles.zip");
dataFile = "ROS_Ouster_Supportfiles.zip";
lidarData = websave(dataFile,dataUrl);

Extract the ZIP file that contains lidar capture data of road intersection.

unzip("ROS_Ouster_Supportfiles.zip")

Load the ROS bag file to retrieve information from it.

bag = rosbag("lidar_capture_of_road_intersection.bag");

Create a BagSelection object that contains the Ouster messages filtered by the topic /os_node/lidar_packets.

bSel = select(bag,"Topic","/os_node/lidar_packets");

Read the messages from the selection. Each element in the msgs cell array is an Ouster ROS message struct. Using messages in structure format supports better performance.

msgs = readMessages(bSel, DataFormat="struct");

Create Ouster ROS Message Reader

The ousterROSMessageReader object reads point cloud data from ouster_ros/PacketMsg ROS messages, collected from an Ouster lidar sensor.

ousterReader = ousterROSMessageReader(msgs,"lidar_capture_of_road_intersection.json")
ousterReader = 
  ousterROSMessageReader with properties:

     OusterMessages: {45342×1 cell}
    CalibrationFile: 'C:\Users\echakrab\OneDrive - MathWorks\Documents\MATLAB\ExampleManager\echakrab.myBdoc\ros-ex32591831\lidar_capture_of_road_intersection.json'
     NumberOfFrames: 709
           Duration: 70.89 sec
          StartTime: 3539.2 sec
            EndTime: 3610.1 sec
         Timestamps: [3539.2 sec    3539.3 sec    3539.4 sec    3539.5 sec    3539.6 sec    3539.7 sec    3539.8 sec    3539.9 sec    3540 sec    3540.1 sec    3540.2 sec    3540.3 sec    3540.4 sec    3540.5 sec    3540.6 sec    …    ] (1×709 duration)
        CurrentTime: 3539.2 sec

Extract Point Clouds

You can extract point clouds from the raw packets message with the help of this ousterROSMessageReader object. By providing a specific frame number or timestamp, one point cloud can be extracted from ousterROSMessageReader object using the readFrame object function. If you call readFrame without a frame number or timestamp, it extracts the next point cloud in the sequence based on the CurrentTime property.

Create a duration scalar that represents one second after the first point cloud reading.

timeDuration = ousterReader.StartTime + seconds(1);

Read the first point cloud recorded at or after the given time duration.

ptCloudObj = readFrame(ousterReader,timeDuration);

Access Location data in the point cloud.

ptCloudLoc = ptCloudObj.Location;

Reset the CurrentTime property of ousterReader to the default value.

reset(ousterReader)

Display Point Clouds

You can also loop through all point clouds in the input Ouster ROS messages.

Define x-, y-, and z-axes limits for pcplayer in meters. Label the axes.

xlimits = [-60 60];
ylimits = [-60 60];
zlimits = [-20 20];

Create the point cloud player and label the axes.

player = pcplayer(xlimits,ylimits,zlimits);
xlabel(player.Axes,'X (m)');
ylabel(player.Axes,'Y (m)');
zlabel(player.Axes,'Z (m)');

The first point cloud of interest is captured at 0.3 second into the input messages. Set the CurrentTime property to that time to begin reading point clouds from there.

ousterReader.CurrentTime = ousterReader.StartTime + seconds(0.3);

Display the point cloud stream for 2 seconds. To check if a new frame is available and continue past 2 seconds, remove the last while condition. Iterate through the file by calling readFrame to read in point clouds. Display them using the point cloud player.

while(hasFrame(ousterReader) && isOpen(player)) && (ousterReader.CurrentTime < ousterReader.StartTime + seconds(2))
ptCloudObj = readFrame(ousterReader);
view(player,ptCloudObj.Location,ptCloudObj.Intensity);
pause(0.1);
end

Figure Point Cloud Player contains an axes object. The axes object with xlabel X (m), ylabel Y (m) contains an object of type scatter.

Reset the CurrentTime property of the reader object to the default value.

reset(ousterReader)

Input Arguments

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Ouster ROS message reader, specified as a object.

Output Arguments

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Indicator of frame availability, returned as a logical 1 (true) when a later frame is available or a logical 0 (false) when a later frame is not available.

Version History

Introduced in R2024a

See Also

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