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Modify source code of a pre-built Package(external)

asked 2013-03-03 06:32:53 -0500

nemesis gravatar image

updated 2013-03-21 21:01:42 -0500

Hi, so I am using a couple packages but the "output" that I get from the nodes isn't exactly what I need to work on.

I wanted to know -

  1. If the source code of these pre-built packages can be modified, and if it can then how do we go about "updating" the package after that?
  2. If I can't modify the source code, can I "manipulate" the output at the nodes before I forward it to other nodes if required?

Thank You!

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What kind of manipulation do you need to do?

Jeffrey Kane Johnson gravatar image Jeffrey Kane Johnson  ( 2013-03-03 16:08:21 -0500 )edit

The coordinates that I get from the package are not along the axes I require. That is, Z direction is Y and X is negative Z. So wanted to check if I can modify the code so that I get it right.

nemesis gravatar image nemesis  ( 2013-03-03 16:14:18 -0500 )edit
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I'm sorry, I should've been clearer. Ignore the previous comment. What I require is - X,Y and Z What the package output is ('cause of the way it's in the code) - X, Z, (negative) Y So I wanted to modify the code to change that. (I hope you understood this time?)

nemesis gravatar image nemesis  ( 2013-03-03 16:27:34 -0500 )edit

Oh, that data format is wrong? Is it publishing a custom message type?

Jeffrey Kane Johnson gravatar image Jeffrey Kane Johnson  ( 2013-03-03 16:31:38 -0500 )edit

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answered 2013-03-03 12:48:43 -0500

joq gravatar image

updated 2013-03-04 01:21:14 -0500

EDIT: to answer both questions:

  1. Check out sources into an overlay and modify that copy. See: http://answers.ros.org/question/47563/how-do-overlays-work/

  2. Write another node that subscribes to the original topic, modifies each message as desired, and republishes it on a different topic name. You'll probably need to remap some topic names for that to work properly.

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I will give this a try. But I guess after modification, I just have to use "Make" inside that folder to compile it, right?

nemesis gravatar image nemesis  ( 2013-03-03 16:09:48 -0500 )edit

It's a good idea to run rosmake first. Later, you can run make, to save build time.

joq gravatar image joq  ( 2013-03-04 01:16:34 -0500 )edit

I will try out the second way later and let you know. But modifying the code worked. Note - I had to use "rosmake", "make" wasn't working. Will update once I figure out why. Thank you!

nemesis gravatar image nemesis  ( 2013-03-04 10:53:30 -0500 )edit
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answered 2013-03-03 16:27:28 -0500

I think I see what you mean. It might be easier to just set up a static transform publisher that puts your coordinates in the right frame, and then add it to your tf tree: http://www.ros.org/wiki/tf#static_transform_publisher

You could also subscribe to the data, apply a transform manually, then republish it.

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Normal modification did work and it's pretty straightforward too. I will look into your procedure and let you know asap. Thank you!

nemesis gravatar image nemesis  ( 2013-03-04 10:54:14 -0500 )edit

@jj56 Modifying it directly worked like I said, but I also wish to add some code to convert a Quaternion set of rotations to Roll Pitch and Yaw. Unfortunately this isn't as easy as I expected it to be. (The source code of the package is in C++ but I am not at all familiar with this part of coding)

nemesis gravatar image nemesis  ( 2013-03-20 10:15:08 -0500 )edit

Any input regarding that?

nemesis gravatar image nemesis  ( 2013-03-20 10:15:24 -0500 )edit

@nemesis ROS has some methods for converting back and forth between rotation representations, have a look here: http://www.ros.org/wiki/geometry/RotationMethods

Jeffrey Kane Johnson gravatar image Jeffrey Kane Johnson  ( 2013-03-20 10:22:23 -0500 )edit

@jj56 - Thank you! That's what I am referring to. I use the getRPY code to try and access the RPY, but that gives me errors/"Note"s when I am trying to actually publish those values. I think since I am not familiar with such codes I am having a hard time figuring out how exactly to show the output.

nemesis gravatar image nemesis  ( 2013-03-20 10:25:38 -0500 )edit

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Asked: 2013-03-03 06:32:53 -0500

Seen: 1,269 times

Last updated: Mar 21 '13