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Scanning with the Riegl LMS-Z210

Author: Blake Hament Email: [email protected]
Keywords: Riegl LMS-Z210, LIDAR, Scan

This Tutorial covers capturing LIDAR scans with the Riegl LMS-Z210 and RiSCAN PRO software.

Motivation and Audience

The Riegl LMS-Z210 is a powerful LIDAR scanner that can be used to capture high resolution point clouds of environments and objects. LIDAR is used in a wide range of robotics sensing applications, and this tutorial will help familiarize you with reading and visualizing LIDAR data.

This tutorial is for those with:

• Interest in LIDAR and robotics
• Experience with installing, configuring, and manipulating computer files

The rest of the tutorial is organized as follows:

1. Parts List and Sources
2. Theory of Operation
3. Setup
4. Scanning
5. Final Words

Parts List and Sources

This tutorial utilizes a Riegl LMS-Z210 and the RiSCAN PRO v1 software, both of which are no longer supported as of the writing of this tutorial. Newer LIDAR sensors, like the Velodyne puck will provide comparable resolution, but they are far smaller and more cost effective. The software was run on a Windows 10 machine.

Theory of Operation

Laser rangefinding works by detecting phase change in light reflected off a target. The sensor sends out light at a known wavelength and then reads the reflected light after it has traveled out to the environment and back to the sensor. Any shifts in the peaks and troughs can be used to calculate phase change.

The distance D between sensor and target can be written,

Where c is the speed of light and t is the time it takes the light to travel from sensor to target and back.

The time t can be expanded

Here, ω is the angular frequency of the light wave, and φ is the phase change between the initial and reflected light rays.

We can expand our equation for D further, substituting the frequency of light f = ω/(4π), then substituting wavelength λ = c/f . Light is a wave, so values repeat every period. Accounting for sign changes, phase changes can be described as (N + ΔN) in which N is an integer number of wave half-cycles and ΔN is the remaining fractional part of the phase change.

Using the above method, a sensor can calculate the phase delay of reflected light and output a distance.

Now, this distance gives the 1D range between the sensor and a point in the environment, but most applications require more data. A common approach is to use a rotating mirror within the sensor to collect light from a series of points in a straight line, usually fanning up to 180 degrees from the sensor. This provides 2D range data. The pictures below show three moments in a 2D LiDAR data collection.

To achieve a full 3D of LiDAR data either: 1) a 2D sensor must be rotated through a range of angles to fan the target environment with the 2D laser paths or 2) the sensor contains multiple spinning mirrors that reflect light throughout the 3D of target environment without moving the sensor itself.

The Riegl combines both methods, using multiple spinning mirrors within a chamber that rotates relative to the base of the sensor.

The following image shows many 2D LiDAR scans combined to visualize 3D.

Setup

First, setup the tripod with the legs spread so that the chains are taunt. Next, attach the scanner to the tripod by holding the bottom of the scanner as you screw it onto the tripod. DO NOT ROTATE the top of the Riegl scanner as this part of the scanner has carefully been calibrated for rotation via internal motors.

Now attach the power, serial, and parallel auxiliary cables to the scanner. You will need the power cord with a right angle male connector. The other end of the power cable should be plugged into a 12V power convertor.

The serial and parallel cables connect to the modem, and the modem requires it's own power cable and 12V power supply. Connect your computer to the modem via an ethernet cable.

When the scanner is plugged into power, the top of the unit should begin rotating.

Installation

You will need RiSCAN PRO and a license key to capture data with the proprietary software. Use Setup.exe to install RiSCAN PRO and enter your license information. After installation is complete, open RiSCAN PRO.

Click “Tool > Options…”

Now make the following changes:

• General → Default scanner settings → Compatibility mode for legacy LMS-Z210 instruments
• Additional → Project manager → Select everything except “AutoExpand and collapse sub trees when clicking on element”

Changing network settings to connect via ethernet: To connect your computer to the scanner via ethernet cable, open “Control Panel > Network and Internet > Network and Sharing Center”.

Now right-click on your Ethernet connection and click “Properties”. Scroll down to “Internet Protocol Version 4 (TCP/IPv4)”, make sure the box is checked, and double-click the text. Now change the setting from “Obtain an IP address automatically” to “Use the following IP addess:”. Enter an IP address on the same subnet as the scanner modem. I used 192.168.0.234 with subnet mask 255.255.255.0. I found the IP address by looking at the log box in RiSCAN PRO when I connected the scanner via ethernet. RiSCAN PRO will detect the scanner at the correct IP address, but it will not connect until you change your computer's ethernet connection to a static IP as described.

Last step: Go back to RiSCAN PRO, open “Tools > Scanner Search”. Enter a range of IP addresses consisting of the IP you set for your ethernet connection and the modem. Select your scanner from the search results.

Scanning

Now its time to start scanning!

“Project > New > Project”

Create a name for your project and save.

Now right-click on the newly created “Scans” folder in your new project directory on the left side of the window and select “New Scanposition”.

A new file should be created called “ScanPos01”. Right-click this file and select “New single scan…”.

The software will now attempt to connect with your scanner. If the connection is successful, a window will appear that allows you to set your scan parameters. If the connection fails, try powering on-and-off the scanner and reconnecting. If the issue persists, you may be need to change your computer's ethernet connection settings. If this is the first time you have connected your computer to the scanner via the modem, you will need to change your network settings as described at the end of the “Installation” section.

Note: Ignore the error message “Supply-Voltage too low: 0.0V, Temperature too low -273.1C”

Set your parameters for scan angles and resolution and take a scan!

Combining and Processing Scan Data

Most projects will require scanning from multiple perspectives and then processing the data into a cohesive visualization of the scan target. Scan data is best combined when the scans have significant overlap, so shoot for about 50% overlap between scans until you have a better feel for the optimum overlap necessary for your specific project.

Once you have several scans with significant overlap saved, choose the scan with the most overlap of other images (usually the most central scan). If the scan with the most overlap is “ScanPos03” for instance, expand the tree associated with this scan in the project manager window, right-click “SOP”, and select “Freeze”. Now the coordinate system from this scan will be used as your “Project Coordinate System” (PRCS), and the points from all other scans will be transformed to this coordinate system.

RiSCANPRO has several methods for combining scans, including manually inputting the distance and rotation between frames and fine-scanning reflective control points. It is my experience that combining these scans can be tricky even with state-of-the-art hardware and software. At the time I write this tutorial, the Riegl LMS-Z210 is already decades old, and successfully combining scans is an exercise in luck and patience.

For questions, clarifications, etc, Email: [email protected]