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static transformer question

asked 2017-01-27 14:26:18 -0500

ghaith gravatar image

Hi I am trying to build a map using slam. I am using Arduino due and Ros indigo, I am capable of building map with few error I have this line in my launch file:

node pkg="tf" type="static_transform_publisher" name="base_to_kinect_broadcaster" args="-0.17 0.04 0.1975 0 0 0 \/base_link \/camera_link 100" />

I need to know if this line is necessary and what the parameter after the arg= mean and how to tune them. this is my main question.

I hope any one can replay with good answer I just need explanation and how to tune the parameter and what exactly this parameter mean.

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Also: not sure whether you added them for the forum, but remove the backslashes (\), they're not needed (nor valid).

gvdhoorn gravatar image gvdhoorn  ( 2017-01-28 05:43:13 -0500 )edit

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answered 2017-01-27 15:28:03 -0500

janindu gravatar image

Quoting tf - ROS,

static_transform_publisher x y z yaw pitch roll frame_id child_frame_id period_in_ms

Publish a static coordinate transform to tf using an x/y/z offset in meters and yaw/pitch/roll in radians. (yaw is rotation about Z, pitch is rotation about Y, and roll is rotation about X). The period, in milliseconds, specifies how often to send a transform. 100ms (10hz) is a good value.

static_transform_publisher x y z qx qy qz qw frame_id child_frame_id period_in_ms

Publish a static coordinate transform to tf using an x/y/z offset in meters and quaternion. The period, in milliseconds, specifies how often to send a transform. 100ms (10hz) is a good value.

To answer your question : The coordinate systems of your camera and base link are different. Each camera image needs to be transformed into the global coordinate system. This transformation happens via the base_link frame. If you run

rosrun tf view_frames

you will see the frames in your system.

To set the arg values properly, identify your base_link coordinate system origin and the camera coordinate system origin, measure the transformation and rotation between the two systems and update x,y,z, roll, pitch, yaw accordingly.

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you mean that I need to identify the origin of the camera related to the base link or related to the ground and is x mean here the desired position on x related to the object or mean something else.i am sry if my question is stupid but just to clear thing for me. thanks for answer,

ghaith gravatar image ghaith  ( 2017-01-28 06:46:27 -0500 )edit

You need to identify the origin of the camera wrt to the base_link. So (x,y,z) is the origin of the camera's coordinate system in base_link coordinate system. Eg: If (0,0,0) in camera's coordinate system is (10,-2,5.5) in the base_link coordinate system, then (x,y,z) is (10,-2,5.5). Same with r,p,y

janindu gravatar image janindu  ( 2017-01-28 10:30:50 -0500 )edit

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Asked: 2017-01-27 14:26:18 -0500

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Last updated: Jan 27 '17