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The relationship of earth frame and map frame [closed]

asked 2021-07-08 10:59:59 -0500

jacklu333333 gravatar image

updated 2021-07-08 11:04:21 -0500

I follow the instruction of REP:105. As it mentioned to have the map frame corrected by the earth frame. So I use imu_filter_madgwick with 9-axis sensor to produce the absolute orientation of the earth and map. Then, use the function provided by the same package to produce the earth and map correction in /tf tree.

However, what I got is the following. the mapping will constant rotation of the map. Hence the rotational mapping result. Mapping in RVIZ

This is my /tf tree. TF Tree

There must be some misunderstanding for me. Please help clarify it. Thanks in advance.

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Closed for the following reason the question is answered, right answer was accepted by jacklu333333
close date 2021-09-24 05:32:23.282126

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answered 2021-07-08 16:00:44 -0500

Mike Scheutzow gravatar image

I would expect the transform from earth->map to be a constant. Any movement of the robot has no effect on the relationship of those 2 frames.

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Hi, thank you for your reply. You point out my blind spot about the relationship of earth->map frame. It should be constant since the map->odom, the rotation measurement would be here.

In that case, I am wondering how can I publish the earth->map relationship at the initial state dynamically since we cannot always assume the North is match to y-asix (for xyz to enu configuration).

Once again thank you for the clarification.

jacklu333333 gravatar image jacklu333333  ( 2021-07-09 04:03:09 -0500 )edit

If you build a map with `rtabmap' and save it, you can then calculate the static rotation needed based on where the map x-axis ended up. Doing this dynamically is more difficult: you will need to read the initial magnetic orientation of the robot once before you begin the rtabmap mapping procedure.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-07-09 06:24:55 -0500 )edit

Thank you for the clarification.

In that case, wouldn't the earth frame a little bit ineffective in most cases since it is always static?

The only case we can apply the earth frame will be when there are multiple robots to do multi-session mapping, in addition, we need to calibrate the orientation of each robot in advance or read once at the beginning.

Is my understanding correct?

jacklu333333 gravatar image jacklu333333  ( 2021-07-12 03:15:19 -0500 )edit

It's not clear on what you are trying to accomplish. Are you trying to 1) create a single, combined map or 2) keep a unique map for each robot and be able to convert between the different map's coordinate systems or 3) something else.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-07-12 06:54:42 -0500 )edit

I think it's more close to 2. Since I want to map the environment as a global map. With the information given by you, I think I can make it work. Thanks a lot.

I am just curious about the necessity of earth frame. Since I can just rotate the map at the mapping session so that XYZ will match to the ENU, in that case, the REP:105 seems unnecessary to define the earth frames, right?

jacklu333333 gravatar image jacklu333333  ( 2021-07-12 07:22:39 -0500 )edit

Since I can just rotate the map at the mapping session so that XYZ will match to the ENU

REP:105 is showing a general architecture. If you choose to transform a rotated map, or somehow pre-initialize the mapN frame so the axes are what you want, then each earth->mapN transform is the Identity transform. Which approach is easiest depends on what you know, and when you know it.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-07-12 10:28:27 -0500 )edit

I got it. Thank you for your time and the detailed explanation.

jacklu333333 gravatar image jacklu333333  ( 2021-07-13 01:58:38 -0500 )edit

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Asked: 2021-07-08 10:59:59 -0500

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Last updated: Jul 08 '21