software_overview.md

Software Overview

The sick_scan_xd software is essentially affected by its use cases:

• Implement the common tasks for different lidars:

  • Provide driver software on Linux and Windows, generic, ROS-1 and ROS-2
  • Receive and convert scan data, publish pointcloud
  • Run startup, configuration and setup

• Use cases:

  • Provide a pointcloud to the customer/application
  • Provide a common highlevel interface for all supported lidars
  • Hide datagram details, encodings and parsing knowhow
  • The most common use case is to run lidar + sick_scan_xd to get a pointcloud.

• Software requirements:

  • Support different lidars (LMS, LRS, LDMRS, MRS, NAV, TiM, RMS, Multiscan, etc.)
  • Support different OS (Linux, Windows)
  • Support different targets (ROS-1, ROS-2, generic)
  • Support different protocols (Cola-A, Cola-B, TCP, UDP, msgpack)
  • Implement parser for different telegrams (scandata, scancfg, fields, etc.)

This overview describes the most important modules and their relationship.

Software structure

The following figures show the most important software blocks:

sick_scan_xd contains 6 main functional blocks:

• sick_generic_caller and sick_generic_laser for initialization and setup:
  • Read configuration from launchfile:
    • ROS1: ros::NodeHandle::getParam
    • ROS2 and generic: LaunchParser (ros-wrapper)
  • Lidar specific setup:
    • class sick_scan::SickGenericParser: lidar specific properties and messages parsing
    • Set and get lidar specific properties: number of layers, angular resolution, etc.
    • Parse and convert scan data, input: scan data (ascii or binary datagram), output: ros::sensor_msgs::LaserScan
    • class sick_scan::SickScanCommonTcp: receive TCP messages, convert and publish pointcloud
  • Start ros services:
    • class sick_scan::SickScanServices: register ros services, convert from/to SOPAS
  • Start monitoring:
    • class sick_scan::SickScanMonitor: monitor scan data, reinit on timeout
    • class sick_scan::PointCloudMonitor: monitor pointcloud, reinit on timeout
• sick_scan_common for the most common lidar devices (LMS, LRS, MRS, NAV, TiM, RMS, etc.):
  • Implemention by SickScanCommon and SickScanCommonTcp
  • Uses SickGenericParser for lidar specific properties and parsing
  • Runs common tasks for LMS/LRS/MRS/NAV/TiM/RMS:
  • Run SOPAS startup sequence
  • Run TCP receiver thread
  • Process telegrams: parse and convert to pointcloud
  • Publish pointcloud
• sick_ldmrs for LDMRS support using the ldmrs-library from https://github.com/SICKAG/libsick_ldmrs.git
• sick_scansegment_xd for Multiscan136 lidars using SOPAS, msgpack and UDP-communication
• sick_scan_services for ros services
• sick_generic_monitoring for monitoring and re-initialization in case of errors (e.g. network errors).

The following figures show these 6 functional blocks:

The function blocks depend on and use the underlying system (ROS, TCP, etc.):

Message receiving and message handling

Message receiving and message handling are decoupled, i.e. both tasks run in separate thread and exchange messages via a FIFO-buffer. This way, message handling can’t block tcp recv and vice versa. The following figure shows the message handling:

The following figure shows the sequence diagram for a LMDscandata telegram:

Incoming TCP messages and exported pointcloud messages are monitored. sick_scan_xd reinitialises the lidar and the tcp connection in case of timeouts.

sick_scansegment_xd

sick_scansegment_xd implements support for Multiscan136 lidars using SOPAS, msgpack and UDP-communication. It has 5 functional blocks:

• class sick_scansegment_xd::MsgPackThreads:
  • Init and run all sick_scansegment_xd components
  • SOPAS startup (Multiscan136, TiMTwo)
• class sick_scansegment_xd::UdpReceiver:
  • Run UDP receiver thread
• class sick_scansegment_xd::MsgPackConverter:
  • Parse and convert msgpacks
  • Collect scan segments
• class sick_scansegment_xd::MsgPackValidator:
  • Validate msgpacks and scansegments
• class sick_scansegment_xd::RosMsgpackPublisher:
  • Publish pointcloud (single segments)
  • Publish cloud_360 (360 pointcloud)

The following figure shows the compoenent diagram for sick_scansegment_xd:

Message receiving, converting and publishing run in 3 separate threads and exchange their messages via a FIFO-buffer.

The following figure shows the sequence diagram for a Multiscan136 msgpacks:

Files and folders

The source files for the sick_scan_xd core can be found in the following folders:

• driver/src: source files
• include: header files
• launch: configuration
• msg: ros messages definitions
• srv: ros services definitions
• roswrap: ros wrapper (ROS-2 and generic)

These folders are required to build sick_generic_caller.

Besides README.md and CHANGELOG.md, all documentation can be found in the doc folder.

Additional folders for sick_scan_xd support, development and test are:

• test: test scripts and emulator
• tools: additional development tools