[Dprglist] Need help with getting a map of the house using RPLidarwith RPi

[Thalanayar Muthukumar]

Thanks Chris for sharing your experiences.
https://www.youtube.com/watch?v=qT5PWlmwydc (~30 secs) - RPLidar mounted on
my robot
It is ready to move around the house

"you need to take the robot’s actual current pose (x, y, theta) into
account" - need to figure out how to do this

On Sun, Nov 21, 2021 at 12:52 PM Chris N <netterchris at gmail.com> wrote:

> Kumar,
>
>
>
> What you are looking for is called an “occupancy grid map”.  There are
> other types of maps, but the occupancy grid map is conceptually the easiest
> one to understand and work with I believe.
>
>
>
> Conceptually, its straight forward how it is created.  This type of map is
> really no different from an image – every pixel corresponds to, for
> example,  one square inch of space, and the pixel values correspond to
> definitely empty (black),   definitely something there (white),   unsure
> (grey).
>
>
>
> In a way, it is just an extension of the real-time display code that you
> have running.  The key differences between real-time display of lidar data
> and using this data to build a map are:
>
>
>
>    1. For map making, you need to take the robot’s actual current pose
>    (x, y, theta) into account.   (For real-time display, you essentially
>    pretend your robot is always at x,y=0,0  and orientation= 0 degrees)
>    2. For map making, you remember the point that is drawn into the map,
>    instead of starting with a clean canvas every cycle
>    3. For map making, the size of your map needs to be larger than the
>    range of your Lidar, otherwise it won’t be of much use.
>
>
>
> You have 3 options:
>
>
>
>    1. Create the algorithm more or less completely from scratch or adapt
>    some sample code that seems to be easy enough to work with.    I’m sure
>    such sample code for python and C++ is out there…. Quick google search
>    found this python code for example:  An occupancy grid mapping example
>    · GitHub
>    <https://gist.github.com/superjax/33151f018407244cb61402e094099c1d>.
>    It says “# This is an implementation of Occupancy Grid Mapping as
>    Presented  in Chapter 9 of "Probabilistic Robotics" By Sebastian Thrun et
>    al.   In particular, this is an implementation of Table 9.1 and 9.2”
>
>    2. Find a library that contains the necessary building blocks.   Maybe
>    all you need is a ready to use grid map data structure along with an API
>    for putting things into that grid map.   Or maybe the library also provides
>    functions that take care of all the processing of the laser scan data.
>    Etc, etc.     Then figure out how to use this library.    MRPT comes to
>    mind but there are probably others.   MRPT – Empowering C++
>    development in robotics <https://www.mrpt.org/>.     OpenSLAM.org
>    (openslam-org.github.io) <https://openslam-org.github.io/> is also a
>    possible resource.
>
>    3. Use ROS and pick one of the mapping algorithms that are available,
>    such as
>       1. Gmapping
>       2. Google cartographer
>       3. etc
>
>
>
>
>
> I have gone down road # 1 and road # 2 some 5+ years ago, but I did not
> reach my destination ☹    I probably didn’t try hard enough…..
>
>
>
> I have also started going down road #3 on more than one occasion, but find
> my self often going in circles and not getting anywhere ☹
>
>
>
> I find that no matter which road you take, it requires a substantial time
> commitment to fully master the underlying technologies.   I find that
> unless I’m at it every day, I start to forget things I’ve learned….
>
>
>
>
>
> Chris.
>
>
>
>
>
>
>
> *From: *Thalanayar Muthukumar via DPRGlist <dprglist at lists.dprg.org>
> *Sent: *Sunday, November 21, 2021 12:36 PM
> *To: *DPRG <dprglist at lists.dprg.org>
> *Subject: *[Dprglist] Need help with getting a map of the house using
> RPLidarwith RPi
>
>
>
> https://learn.adafruit.com/slamtec-rplidar-on-pi/cpython-on-raspberry-pi - The
> relevant code is below
>
> def process_data(data):
>
>     global max_distance
>
>     lcd.fill((0,0,0))
>
>     for angle in range(360):
>
>         distance = data[angle]
>
>         if distance > 0:                  # ignore initially ungathered data points
>
>             max_distance = max([min([5000, distance]), max_distance])
>
>             radians = angle * pi / 180.0
>
>             x = distance * cos(radians)
>
>             y = distance * sin(radians)
>
>             point = (160 + int(x / max_distance * 119), 120 + int(y / max_distance * 119))
>
>             lcd.set_at(point, pygame.Color(255, 255, 255))
>
>     pygame.display.update()
>
> This code is used to update the TFT display and is working for me.
> Instantaneously, the RPLidar's surroundings are displayed on the TFT
> display. I would like to adapt this to move the RPLidar through the rooms
> of the house to create a map. @Chris - Any suggestions or pointers? I do
> not have ROS installed. Regards. - Kumar
>
>
>
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