Velodyne VLP16 frequency too low
Hey guys,
Im running a velodyne VLP16, however i am having issues with it's publish frequency, this lidar is spinning at 600 rpm with a packet rate of 754. The /diagnostics
topic for the velodyne_nodelet_manager
currently show's this:
values:
-
key: "Events in window"
value: "46"
-
key: "Events since startup"
value: "2774"
-
key: "Duration of window (s)"
value: "10.884267"
-
key: "Actual frequency (Hz)"
value: "4.226284"
-
key: "Target frequency (Hz)"
value: "9.921053"
-
key: "Minimum acceptable frequency (Hz)"
value: "8.928947"
-
key: "Maximum acceptable frequency (Hz)"
value: "10.913158"
-
key: "Earliest timestamp delay:"
value: "0.000624"
-
key: "Latest timestamp delay:"
value: "0.000779"
-
key: "Earliest acceptable timestamp delay:"
value: "-1.000000"
-
key: "Latest acceptable timestamp delay:"
value: "5.000000"
-
key: "Late diagnostic update count:"
value: "0"
-
key: "Early diagnostic update count:"
value: "0"
-
key: "Zero seen diagnostic update count:"
value: "0"
You can see that i should be getting a frequency of around 10hz, however the actual frequency is only around 4.1hz. Does anyone have any idea what could be the cause of this?
Here are some more outputs:
rostopic bw /velodyne_points
average: 3.77MB/s
mean: 0.90MB min: 0.89MB max: 0.90MB window: 29
rostopic hz /velodyne_points
average rate: 4.196
min: 0.216s max: 0.276s std dev: 0.02812s window: 20
rostopic bw /velodyne_packets
average: 434.13KB/s
mean: 92.29KB min: 92.29KB max: 92.29KB window: 9
The velodyne_nodelet_manager
seems to be using about 0.6% of memory and 2% of cpu, and the computer i am streaming the lidar too does not show any signs of computational burden
I should also note from a hardware layer perspective the lidar run's through a gigabit switch
Asked by agurman on 2019-05-21 22:17:25 UTC
Answers
I managed to resolve this issue. For anyone encountering this in the future, within the configuration web interface for the VLP-16 there is a parameter called FOV Start
which allows you to crop the data being sent between two angles. If you are using this parameter there seems to be either a bug, or performance issue where it drastically drops the frequency. Restoring this to the default 0 to 359 range allowed me to attain the desired 10hz frequency.
The velodyne ros package has a few parameters that allow you to crop the range of the data within the node itself without impacting negatively on frequency performance.
Asked by agurman on 2019-05-28 00:25:49 UTC
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