reset
Reset CurrentTime
property of
velodyneROSMessageReader
object to default value
Since R2020b
Syntax
Description
reset(
resets the
veloReader
)CurrentTime
property of the specified velodyneROSMessageReader
object to the default value. The default value is the
value of the StartTime
property of the velodyneROSMessageReader
object.
Examples
Work with Velodyne ROS Messages
This example shows how to handle VelodyneScan
messages from a Velodyne LiDAR.
Velodyne 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 Velodyne ROS messages for easy use.
Prerequisites: Work with Basic ROS Messages
Load Sample Messages
Load sample Velodyne messages. These messages are populated with data gathered from Velodyne LiDAR sensor.
load("lidarData_ConstructionRoad.mat")
VelodyneScan Messages
VelodyneScan
messages are ROS messages that contain Velodyne LIDAR scan packets. You can see the standard ROS format for a VelodyneScan
message by creating an empty message of the appropriate type. Use messages in structure format for better performance.
emptyveloScan = rosmessage("velodyne_msgs/VelodyneScan","DataFormat","struct")
emptyveloScan = struct with fields:
MessageType: 'velodyne_msgs/VelodyneScan'
Header: [1×1 struct]
Packets: [0×1 struct]
Since you created an empty message, emptyveloScan
does not contain any meaningful data. For convenience, the loaded lidarData_ConstructionRoad.mat
file contains a set of VelodyneScan
messages that are fully populated and stored in the msgs
variable. Each element in the msgs
cell array is a VelodyneScan
ROS message struct. The primary data in each VelodyneScan
message is in the Packets
property, it contains multiple VelodynePacket
messages. You can see the standard ROS format for a VelodynePacket message by creating an empty message of the appropriate type.
emptyveloPkt = rosmessage("velodyne_msgs/VelodynePacket","DataFormat","struct")
emptyveloPkt = struct with fields:
MessageType: 'velodyne_msgs/VelodynePacket'
Stamp: [1×1 struct]
Data: [1206×1 uint8]
Create Velodyne ROS Message Reader
The velodyneROSMessageReader
object reads point cloud data from VelodyneScan
ROS messages based on their specified model type. Note that providing an incorrect device model may result in improperly calibrated point clouds. This example uses messages from the "HDL32E"
model.
veloReader = velodyneROSMessageReader(msgs,"HDL32E")
veloReader = velodyneROSMessageReader with properties: VelodyneMessages: {28×1 cell} DeviceModel: 'HDL32E' CalibrationFile: 'M:\jobarchive\Bdoc21b\2021_06_16_h16m50s15_job1697727_pass\matlab\toolbox\shared\pointclouds\utilities\velodyneFileReaderConfiguration\HDL32E.xml' NumberOfFrames: 55 Duration: 2.7477 sec StartTime: 1145.2 sec EndTime: 1147.9 sec Timestamps: [1145.2 sec 1145.2 sec 1145.3 sec 1145.3 sec 1145.4 sec 1145.4 sec 1145.5 sec 1145.5 sec 1145.6 sec 1145.6 sec 1145.7 sec 1145.7 sec 1145.8 sec 1145.8 sec 1145.9 sec 1145.9 sec … ] CurrentTime: 1145.2 sec
Extract Point Clouds
You can extract point clouds from the raw packets message with the help of this velodyneROSMessageReader
object. By providing a specific frame number or timestamp, one point cloud can be extracted from velodyneROSMessageReader
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 = veloReader.StartTime + seconds(1);
Read the first point cloud recorded at or after the given time duration.
ptCloudObj = readFrame(veloReader,timeDuration);
Access Location
data in the point cloud.
ptCloudLoc = ptCloudObj.Location;
Reset the CurrentTime
property of veloReader
to the default value
reset(veloReader)
Display All Point Clouds
You can also loop through all point clouds in the input Velodyne 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.
player = pcplayer(xlimits,ylimits,zlimits);
Label the axes.
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.
veloReader.CurrentTime = veloReader.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(veloReader) && isOpen(player) && (veloReader.CurrentTime < veloReader.StartTime + seconds(2))) ptCloudObj = readFrame(veloReader); view(player,ptCloudObj.Location,ptCloudObj.Intensity); pause(0.1); end
Input Arguments
veloReader
— Velodyne® ROS message reader
velodyneROSMessageReader
object
Velodyne ROS message reader, specified as a velodyneROSMessageReader
object.
Version History
Introduced in R2020b
See Also
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