# Converting raw Lidar data to something more useful

**URL:** <https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533>\
**Category:** ROS General\
**Created:** [July 28, 2018, 11:17am UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533 "2018-07-28T11:17:01Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![pitosalas](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/pitosalas/32/698_2.png) [@pitosalas](https://discourse.openrobotics.org/u/pitosalas)\
**Post date:** [July 28, 2018, 11:17am UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/1 "2018-07-28T11:17:01Z")

</div>

I have a small robot (turtlebot3) with a Lidar. For aa demonstration I would like to process the data coming from the lira in the following way:

1. Pay attention only to a range of angles (e.g. -15 degrees to +15 degrees)
2. Filter it into  
a) distance to obstacle  
b) rate of change of a)  
c) rate of change of b)

I am assuming that this is elementary and there are nodes/libraries in ROS that do just this. I am not asking for code but pointers to where to look and what to read. Thanks for your help!

---

<div class="post-metadata">

**Author:** ![sjp](https://avatars.discourse-cdn.com/v4/letter/s/bc8723/32.png) [@sjp](https://discourse.openrobotics.org/u/sjp)\
**Post date:** [July 28, 2018, 1:16pm UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/2 "2018-07-28T13:16:32Z")

</div>

Might get more responses if you post this on [ROS answers](https://answers.ros.org/questions/)

---

<div class="post-metadata">

**Author:** ![pitosalas](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/pitosalas/32/698_2.png) [@pitosalas](https://discourse.openrobotics.org/u/pitosalas)\
**Post date:** [July 28, 2018, 1:27pm UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/3 "2018-07-28T13:27:32Z")

</div>

Yeah the mysteries of what folks accept here vs. ros answers. It’s a constant thing.

---

<div class="post-metadata">

**Author:** ![tfoote](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/tfoote/32/3813_2.png) [@tfoote](https://discourse.openrobotics.org/u/tfoote)\
**Post date:** [July 29, 2018, 1:30am UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/4 "2018-07-29T01:30:40Z")

</div>

Please read the [Support guidelines](http://wiki.ros.org/Support) for what to post here versus [answers.ros.org](http://answers.ros.org).

At the most simple a question should go on [answers.ros.org](http://answers.ros.org). So this would be more appropriate on [answers.ros.org](http://answers.ros.org) as it’s a question.

---

<div class="post-metadata">

**Author:** ![mch](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/mch/32/846_2.png) [@mch](https://discourse.openrobotics.org/u/mch)\
**Post date:** [July 30, 2018, 5:57pm UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/5 "2018-07-30T17:57:13Z")

</div>

ROS has a wrapper ([pcl - ROS Wiki](http://wiki.ros.org/pcl)) for Point Cloud Library ([http://pointclouds.org](http://pointclouds.org)) which has a lot of functionality to process lidar data. To cut out certain region from PointCloud you may want to take a look at PassThrough filter ([http://pointclouds.org/documentation/tutorials/passthrough.php](http://pointclouds.org/documentation/tutorials/passthrough.php)).

---

<div class="post-metadata">

**Author:** ![pitosalas](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/pitosalas/32/698_2.png) [@pitosalas](https://discourse.openrobotics.org/u/pitosalas)\
**Post date:** [July 30, 2018, 8:10pm UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/6 "2018-07-30T20:10:22Z")

</div>

Interesting, I will dig into that. Thanks!

---

<div class="post-metadata">

**Author:** ![pitosalas](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/pitosalas/32/698_2.png) [@pitosalas](https://discourse.openrobotics.org/u/pitosalas)\
**Post date:** [July 30, 2018, 8:14pm UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/7 "2018-07-30T20:14:58Z")

</div>

I tried it on answers and didn’t get any answers. Here I did get a couple of useful ones. So if “questions” are supposed to go onto [answers.ros.org](http://answers.ros.org) then discourse is only for announcements and declarations and actually not for any _discourse_.

I’m only being somewhat ironic. I thought of answers for geeky detailed questions about ROS (like stack overflow) and discourse for more conceptual, theoretical, and general questions. This is I guess a misunderstanding.

For example I had such a general question: “If I want to process the liar data so that I can find out a good current estimate of the closet obstacle plus its rate of change, should I be learning about Kaman filters or is that the wrong kind of processing?” I would have posted that question here. But I guess I will try somewhere else, right?

---

<div class="post-metadata">

**Author:** ![gbiggs](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.openrobotics.org/gbiggs/32/30361_2.png) [@gbiggs](https://discourse.openrobotics.org/u/gbiggs)\
**Post date:** [July 30, 2018, 10:03pm UTC](https://discourse.openrobotics.org/t/converting-raw-lidar-data-to-something-more-useful/5533/8 "2018-07-30T22:03:09Z")

</div>

Actually I think that particular non-ROS-specific question would probably get answered quickest on the [robotics stack exchange](https://robotics.stackexchange.com/).