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LaserScan time_increment

asked 2014-05-09 04:37:59 -0500

Hansg91 gravatar image


Following a previous question I was wondering what the time_increment in the LaserScan message is for.

The LaserScan.msg says:

float32 time_increment   # time between measurements [seconds] - if your scanner
                         # is moving, this will be used in interpolating position
                         # of 3d points

However isn't this nothing more than scan_time / ranges.size() ? Seems a bit redundant? In addition, we had this value filled in and it for some reason caused our messages to receive a noticeable delay in rviz. Setting it back to 0 'fixed' this issue.

Best regards, Hans

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answered 2014-05-09 05:30:43 -0500

dornhege gravatar image

Caution speculation on my part: I believe the difference to scan_time/ranges.size() is supposed to account for the dead time, when e.g. a 240 deg laser is making a full revolution. The time increment in this case is probably 240/360*scan_time/ranges.size().

As to rviz: This is likely due to the fact that transformations now have to be computed for each individual ray instead of once per scan. However, if algorithms can run "more correct" I would not stay away from this feature due to the visualization, but rather fix rviz.

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As in, make rviz ignore the time_increment value? It is possible the value I had was wrong, but it all just seemed very weird in rviz.

Hansg91 gravatar image Hansg91  ( 2014-05-09 12:05:29 -0500 )edit

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Asked: 2014-05-09 04:37:59 -0500

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Last updated: May 09 '14