[ros-users] swissranger_camera Issues

Ulrich Friedrich Klank klank at in.tum.de
Thu May 6 11:34:52 UTC 2010

Hi Bill,

I made the experience that image transport over USB usually introduces a 
relatively high lag. Given your camera is on a bus with lower latency 
(like firewire), you might just have an constant temporal offset.

In dev_sr.cpp at line 196 the assumption is made, the the image is 
acquired synchronously, meaning, that function SR_Acquire trigger the 
acquisition of an image on the swissranger and transport this image back 
to the pc, which might not be correct. More probably SR_Acquire just 
copies the last image on the usb communication stack of the driver to 
the user memory, or waits for the next arriving image, if there is 
nothing in queue.

You most probably can fix your problem by adding a constant offset to
timestamp at this point in the file depending on the overall framerate 
and the transportation time over the usb-bus.

A Calibration of this offset would require most probably a lot of 
accurate hardware to produce a unique signal in the the swissranger for 
a precisesly known time. Sorry to not be able to tell anything about 
this delay, since we currently use the swissranger only under a static 
world assumption.

Please keep us informed if you find out about this latency.
Good luck,
Ulrich Klank

Bill Morris wrote:
> Hello,
> I'm working with the SR4K and the swissranger_camera driver on
> boxturtle. I was wondering if there was any calibration procedures for
> the driver.
> I got the point cloud running in rviz with a camera and it looks like
> the data from the sr4k is lagging behind the color camera images by a
> few tenths of a second. Does anyone have any ideas as to the cause of
> this? I tried adjusting the integration time, but that did not seem to
> help.
> Thanks,
> -Bill
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Ulrich Klank                        klank at in.tum.de
Technische Universität München | Boltzmannstr 3 |
85748 Garching bei München  | Germany
www9.in.tum.de/people/klank | Tel: +49 89 289 - 17777

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