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_xd::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_xd::SickScanCommonTcp: receive TCP messages, convert and publish pointcloud

  • Start ros services:

    • class sick_scan_xd::SickScanServices: register ros services, convert from/to SOPAS

  • Start monitoring:

    • class sick_scan_xd::SickScanMonitor: monitor scan data, reinit on timeout

    • class sick_scan_xd::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 and picoScan150 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 cannot 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 and picoScan150 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, picoScan150)

• 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_fullframe (fullframe pointcloud, 360 deg for Multiscan136 resp. 270 deg for picoscan)

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