ROS2 Parameter Demo - Workflow Components

This project contains a ROS2-based ultrasonic data acquisition and processing system with real-time visualization and parameter control capabilities.

The following README is for Evo devices which may use a different set of parameters. The logics should be identical though.

Overview

The system consists of three main ROS2 nodes that work together:

1. Publisher Node (publisher.py) - Interfaces with Evo hardware to acquire ultrasonic A-scan data
2. Processor Node (processor.py) - Processes raw A-scan data and displays real-time visualizations
3. Controller Node (controller.py) - Provides a GUI for monitoring and controlling system parameters

Architecture

┌─────────────────┐      Ascan Message      ┌─────────────────┐
│                 │ ──────────────────────> │                 │
│    Publisher    │                         │    Processor    │
│  (Hardware I/O) │                         │ (Visualization) │
└─────────────────┘                         └─────────────────┘
         ↑                                           ↑
         │                                           │
         │          ROS2 Parameters                  │
         └───────────────────┬───────────────────────┘
                             │
                    ┌────────────────┐
                    │   Controller   │
                    │     (GUI)      │
                    └────────────────┘

Components

Publisher Node (ascan_publisher)

Purpose: Interfaces with Evo ultrasonic hardware to acquire A-scan waveform data from up to 2 channels.

The publisher does not include code on temperature gathering. You should implement your own temperature aquisition code, and there is a segment in the code where you can do this.

Parameters:

• numAverages (int, 1-1000): Number of waveform averages for noise reduction
• numChannels (int, 1-2): Number of active channels
• numCycles (int, 1-3): Number of excitation cycles (read-only)
• numSamples (int): Number of samples to record (read-only)
• signalFrequency (int): EMAT signal frequency in Hz

Published Topics:

• /ascan (interfaces/msg/Ascan): Contains active channels, encoded waveform data, and temperature

Processor Node (ascan_processor)

Purpose: Processes raw A-scan data and provides real-time visualization with automatic peak detection.

Key Features:

• Real-time matplotlib-based visualization for active channels
• Automatic subplot arrangement based on number of active channels
• Peak detection and thickness calculation
• Multiple processing modes (first peak, multi-echo, zero crossing)
• Temperature-corrected measurements

Parameters (per channel, ch1-ch2):

• ch{N}_sampling_freq (int): Sampling frequency in Hz
• ch{N}_lowbound_time (int): Lower bound time in microseconds
• ch{N}_minimum_thickness (float): Minimum detectable thickness in mm
• ch{N}_wave_velocity (float): Wave velocity in m/s
• ch{N}_num_cycles (float): Number of cycles for processing
• ch{N}_signal_frequency (int): Signal frequency in Hz
• ch{N}_threshold_snr (float): SNR threshold in dB
• ch{N}_noise_width (int): Noise calculation window width
• ch{N}_calibration_index (int): Calibration reference index
• ch{N}_firstPeak (bool): Enable first peak detection mode
• ch{N}_multiEcho (bool): Enable multi-echo mode
• ch{N}_zeroCrossing (bool): Enable zero crossing detection
• ch{N}_temperatureCorrected (bool): Enable temperature correction

Subscribed Topics:

• /ascan (interfaces/msg/Ascan): Receives waveform data from publisher

Controller Node (parameter_manager_gui)

Purpose: Provides a PyQt5-based GUI for real-time parameter monitoring and control.

Key Features:

• Automatic discovery of ROS2 nodes and their parameters
• Tabbed interface with separate tabs for each active channel
• Parameter filtering based on configuration file
• Support for various parameter types (sliders, spinboxes, checkboxes)
• Real-time parameter updates with visual feedback
• Configurable display names and parameter bounds

Configuration (config.json):

• multipleTabs: Enable/disable tabbed interface
• whitelist: Enable parameter whitelisting
• hideReadOnlyParameters: Hide read-only parameters
• whitelistNodes: List of nodes to display
• whitelistParameters: Parameters to show per node
• parameterDisplayNames: Custom display names for parameters
• parameter_bounds: Min/max bounds for numeric parameters

Channel Numbering

The system uses 1-based channel numbering (1-2) for user-facing interfaces:

• Channel parameters are named ch1_* through ch2_*
• Display shows "Channel 1" through "Channel 2"
• The channelsOnReceive parameter uses array indices 0-1 internally but presents channels as 1-2 to users

Message Format

Ascan Message

int32[] active_channels   # List of active channel numbers (1-2)
string[] ascan_data       # Base64-encoded waveform data for each active channel
float32 temperature       # Current temperature reading
int32 signal_frequency    # EMAT pulser frequency

Dependencies

• ROS2 Humble or later (tested on Jazzy) (Desktop Variant is required for processor and controller)
• Evo ultrasonic system (for publisher)

Installation

1. Under the project root folder, run

cd drivers
sudo ./sonobotics_runtime_<version&architecture>.deb
sudo ./sonobotics_waveforms_<version&architecture>.deb
tar -xvf pololu-jrk-g2-1.4.0-linux-x86.tar.xz
cd pololu-jrk-g2-1.4.0-linux-x86
sudo ./install.sh

2. Once drivers have been installed, run

colcon build

to build all the packages.

Usage

Starting the System

1. Launch the publisher node (requires Evo hardware):

ros2 run ros_parameter_demo publisher

2. Launch the processor node for visualization:

ros2 run ros_parameter_demo processor

3. Launch the controller GUI:

ros2 run ros_parameter_demo controller

Configuring Channels

To enable specific receive channels, modify the numChannels parameter in the publisher file.

Processing Modes

Each channel can operate in different processing modes:

• First Peak: Detects the first significant peak in the waveform
• Multi-Echo: Processes multiple reflections
• Zero Crossing: Uses zero-crossing detection for improved accuracy
• Temperature Corrected: Applies temperature compensation to measurements

Note: First Peak and Multi-Echo modes are mutually exclusive.

If you set both in the controller, the processor falls back to which none of the four parameters are set.

Configuration Files

• config.json: Controller GUI configuration
• Channel parameters can be saved/loaded via ROS2 parameter services

Troubleshooting

1. No visualization appears: Ensure at least one channel is enabled in numChannels
2. Controller doesn't show parameters: Controller won't show anything until the publishing node is on. Check that nodes are running and config.json whitelist is correct.
3. Hardware errors: Verify Evo device is connected and permissions are set correctly.