LiDART

(Light Detection And ranging using Triangulation)

This project was created within the academic space, thus it is considered as EXPERIMENTAL code. This program intends to obtain a point-cloud of the surrounding using triangulation.

Programs

The Project is divided in two main programs:

• LiDART (main)
• Point generator (branch coord_generator)

LiDART is capable of displaying in the GUI the point-cloud while the point-generator was the funtionality of solely outputing the point coordinates to a .txt file.

Setup details

To run this setup, it was used:

• Linux 20.04 LTS
• ROS based system(noetic version)
• Cameras : IDS imaging UI-3260CP-M/C in stereo configuration
• Mirror: Optotune MR 15-30
• Laser : Thorlabs - HL6738MG
• Trigger: in-house developed system with a pulse with 100us
• Camera baseline: 0.5 meters

Setup explanation

In the GUI, the user inputs:

• Horizontal FoV
• Vertical FoV
• Horizontal step
• Vertical step
• Horizontal offset
• Vertical offset

(The last 2 can be set to 0)

The cameras and the laser are sincronzed by a trigger. When pressed, the laser emits a laser spot that is captured by the cameras. The mirror will redirect the laser spot to the different coordinates. The photos will be collected and processed in the PPUnit.cpp that will output the an Z,Y,Z coordinate.

Installation

Since the setup was run in ROS, I used ROS noetic. It is necessary to install OpenCV https://opencv.org/ .

The cameras used come with proprietary software in order to connect them to the computer. I found a very usefull ROS package named ueye_cam from https://wiki.ros.org/ueye_cam . It creates the nodes for the cameras when connected.

git clone https://github.com/anqixu/ueye_cam.git

From there, we need to connect the mirror to the linux environment. Originally, the software provived by the Optotune isn't compatible with LINUX. With that, it was necessary to install the same libraries provided by the manufacture, but in LINUX, in this case:

• numpy 1.9.1
• pyserial 2.7

The simpler way to install the code on your computer is to setup a ROS environment using https://wiki.ros.org/ROS/Installation Then, after that, create a package using

catkin_create_pkg nameofthepackage std_msgs rospy roscpp sensor_msgs image_transport cv_bridge

Then import the folders inside the git /src to the src created in the ROS package. Finally add to the CMakeList.txt

add_executable (PPUnit src/PPUnit.cpp)
target_link_libaries(PPUnit ${catkin_LIBRARIES} ${OpenCV_LIBRARIES})

add_executable (camera_subscriber src/camera_subscriber_test.cpp)
target_link_libaries(PPUnit ${catkin_LIBRARIES})

How to run the setup

The programs necessary to run the setup are:

• PPUnit : It's considered the processing unit. It receives the photos from the image nodes, finds the centroids, triangulates and creates the pointcloud.
• mirror_laser : This program initializes the cameras and laser trigger and the mirror. It communicates with all the different nodes
• dashboard : The GUI. It allows the user to define the parameters.
• ueye_cam( stereo_cameras_trigger.launch) : it launches both cameras

Before running anything it is important to check for 2 things: - if running in a VM( in my case VMWare, VMWare has a feature called removable devices), there is a list of all the devices connected to the computer, it is possible that some by not be in the connected state by default. Check that before anything else - Run the command dmesg in the terminal to check what devices are connected to what. It is possible that the ports the trigger might have changed.

To start ROS, open a terminal(I recomend terminator) and write:

roscore

Then, start all the different files:

roslaunch lidart_workspace stereo_camera_trigger.launch
rosrun lidart_workspace mirror_laser.py
rosrun lidart_workspace PPUnit
rosrun lidart_workspace dashboard.py

After that, and if no problems arise, the program is ready to run.

Variations

There is a couple of variations to the main purpose of the file. The file camera_trigger.py can be used to only trigger the cameras, when the mirror nor the laser are connected.

Run the cameras

In order to run the cameras it is necessary to use the third party library created by anqixu(https://github.com/anqixu/). When opening the repo, the path is :

~/catkin_ws/src/ueye_cam/launch/

In order to trigger to cameras with the specs used in this project, it was created two launch files for this purpose:

• stereo_cameras_no_trigger.launch
• stereo_cameras_trigger.launch

Depending on which application the user wants to use the setup(having an external trigger to actuate both cameras at the same time(....trigger.launch) or other application where the trigger isn't important(...._no_trigger.launch)).

To launch either file:

roslaunch ueye_cam stereo_cameras_trigger.launch

Possible error and solutions:

• It might be useful to have the ids manager application installed. Despite not being used, it is possible to quickly check whether a camera is being identified by the computer.
• These cameras require a higher voltage than normal USB devices. If your computer doesn't recognized the cameras it is possible that 2 things are happening:
  • The IDS driver isn't installed
  • The USB power the computer is supplying isn't enough
    • For this reason it is necessary to have a USB hub that can be powered externally.

Any change made to the .cpp files needs to be completed with catkin_make. Also, if created any .cpp file, it is necessary to add an entry to the CMakeList.txt. In the case of python files, there isn't the need to add nothing to the CMakeList.txt