What is the "center of the robot" in costmap_2d's footprint?

asked 2015-09-14 15:26:18 -0600

kwiesz91
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In the robot setup navigation tutorial, it says:

"In the case of specifying the footprint, the center of the robot is assumed to be at (0.0, 0.0)..."

From this, it sounds like they want it to be the actual center of the robot, but then how does it relate this to the center of rotation, which is used everywhere else? Because in my case, I have static transforms that relate the sensor positions to the center of rotation, not the actual center of the robot.

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what is "everywhere else" where they refer to the center of rotation?

mgruhler ( 2015-09-15 10:02:27 -0600 )edit

I should have just said: "...but then how does this relate to the base_link"

kwiesz91 ( 2015-09-15 10:38:53 -0600 )edit

alright ;-)

mgruhler ( 2015-09-15 10:42:00 -0600 )edit

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answered 2015-09-15 10:01:59 -0600

mgruhler

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As they say

In the case of specifying the footprint, the center of the robot is assumed to be at (0.0, 0.0)...

This means, when you specify the footprint, you have to specify the endpoints relative to where YOU put the center (and this means, the base_link) of the robot. It does not need to be the actual center. This depends on your robot, application and base kinematics.

E.g., there are some common locations you put the base_link of the robot, that depend on the kinematics. For omnidirectional robots, most people have it as the physical center of the robot. For differential drive robots, it usually is the middle of the axis of the two driven wheels, independently of the physical dimensions of the robot.

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Thank you so much. This is the exact answer i was looking for. Maybe I'm crazy in thinking that the text could be a little clearer? Or maybe it can just blatantly say "the center is where you have your base_link" for people like me.

kwiesz91 ( 2015-09-15 10:36:01 -0600 )edit

Well, having this as base_link is also just a convention. Actually, for the costmaps, you have the parameter robot_base_frame which could be set to something else.

mgruhler ( 2015-09-15 10:49:18 -0600 )edit

I figured, but good point.

kwiesz91 ( 2015-09-15 12:32:11 -0600 )edit

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What is the "center of the robot" in costmap_2d's footprint?

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