depth_image_raw impossibly slow across machines (wireless)
Hi,
I've spun up realsense2camera. Depth messages are being produced on the robot's PC without issue. I'm looking to see that output on a remote machine (I've tried both VM and non VM) - for now in RVIZ (later used to drive rtabmap). All other, scan, map, sensor data is fine but depthimage_raw and any other image data is impossibly slow. For example:
rostopic hz /camera/depth/image_rect_raw
yields:
On robot:
average rate: 29.975
min: 0.023s max: 0.044s std dev: 0.00097s window: 19608
On Remote PC
average rate: 0.031
min: 22.248s max: 47.057s std dev: 7.42743s window: 20
Additional Details:
rostopic echo -n1 --noarr /camera/depth/image_rect_raw
header:
seq: 421
stamp:
secs: 1678046085
nsecs: 714776278
frame_id: "camera_depth_optical_frame"
height: 480
width: 848
encoding: "16UC1"
is_bigendian: 0
step: 1696
data: "<array type: uint8, length: 814080>"
---
rostopic type /camera/depth/image_rect_raw
sensor_msgs/Image
So far I've checked the router, WiFi, Network bandwidth and all are fine/well within parameters.
If anyone has any suggestions WRT what else I can check I'd most appreciate it.
Thanks
Mark
Asked by MarkyMark2012 on 2023-03-04 12:16:25 UTC
Answers
Just run iperf in both directions from Robot to PC and back over 60 secs combined average about 34.3Mbits/sec.
iwconfig output:
wlx74da38733b6f IEEE 802.11 ESSID:"NeonStar2" Mode:Managed Frequency:2.422 GHz Access Point: 00:1D:AA:5E:85:A8 Bit Rate=72.2 Mb/s Tx-Power=20 dBm Retry short limit:7 RTS thr=2347 B Fragment thr:off Power Management:off Link Quality=70/70 Signal level=-33 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:0 Missed beacon:0
So that's indeed all megabit/sec, not megabyte/sec.
Maximum theoretical bw between your two hosts over wireless would then be about 7 MB/sec, which is about 10x lower than what you stated earlier, and over 3x less than what would be needed to transmit just the depth images (at 24.5 MB/sec), if everything worked perfectly.
Your iperf results suggest the actual attainable bw is less than half the max, at 34 mbit/sec, or just about 3.5 MB/sec (that could make sense for a half-duplex medium). That would reduce available bw for depth images by another factor of 2.
Still not claiming it's just bw that's the issue here, but it's likely a big factor.
What brand/model wireless nic and router do you have? You could check whether it's capable of wider channels to increase available bw.
Asked by gvdhoorn on 2023-03-07 06:00:49 UTC
Comments
Btw: it's not something often done, but as depth images are basically just that, images, you can use image_transport and compress them. Using a lossless compression plugin should still result in decent compression while not affecting image quality (and ultimately, depth quality).
Something to consider perhaps.
Asked by gvdhoorn on 2023-03-07 06:09:26 UTC
Thanks for that. Next port of call I think I'll get a new WiFi adapter. Possibly look at the compression to.
The WiFi adapter is an Edimax dongle - I forget which one. Router is Vigor - can't remember the model off hand.
Will have a look at something along the lines of:
Asked by MarkyMark2012 on 2023-03-07 08:32:03 UTC
Comments
that's a good starting point, but without sharing what you found and what conclusions you've drawn based on that data, board members here are only going to be able to guess.
I would suggest to add at least the output of
rostopic type /camera/depth/image_rect_rawandrostopic echo -n1 --noarr /camera/depth/image_rect_rawto your post.Any
image*rawtopic at any reasonable resolution will result in significant bandwidth usage, which is a common cause for slow message rates.Additionally, since you mention "WiFi": large messages over a regular TCPROS transport over a (very) lossy link may require retransmits of multiple packets (note: not messages). Over time those can add up to a significant delaying factor.
Asked by gvdhoorn on 2023-03-05 08:24:51 UTC
Thanks - I've updated the question with additional info. Checked other various WiFi stats - no dropped packets (noted: re: packets vs messages) . rostopic bw /camera/depth/image_rect_raw shows about 24.5MB/s
WiFi Link is capable (iwconfig) 72.2MB/s
Nothing else on the LAN (Dedicated WiFi router atm for the sake of trouble shooting). I would expect there to be a drop in performance across the network but this seems to just drop off a cliff.
Asked by MarkyMark2012 on 2023-03-05 15:05:59 UTC
please share the output of
iwconfigverbatim. If you're looking at theratefield: that's instantaneous, max, theoretical bw configuration. Not actual transfer rate. Sustained, perfect (ie: zero lost pkts) transfer at the data rates you are using is not something I'm accustomed to over a wireless link.I would also check
Mb/svsMB/s. There's a factor 8 difference there (with overhead: about 10x actually), and72 Mb/scould make sense to me: it's one of the typical wireless datarates supported by cards.As a diagnostic step: if you can, try using a wired connection and see whether the same delays and bw issues appear.
Also: you could try using
iperfto benchmark actual available bw on your wireless link.I agree with you the
hzoutput is very low, but I'd first check bw.Asked by gvdhoorn on 2023-03-06 02:34:39 UTC
Just run iperf in both directions from Robot to PC and back over 60 secs combined average about 34.3Mbits/sec.
iwconfig output:
I'll give hardwire a go in a day or 3
Asked by MarkyMark2012 on 2023-03-07 05:57:18 UTC