Laser Scanning - Renishaw SLM (XML) - 20

Description

Driver to control and decode data from a Renishaw Scanning Laser Module.

This SLM unit can be a stand alone system, or part of a Renishaw configuration, combining accurate GNSS, an INS and one or two Laser Scanning Heads, already fully calibrated for mounting angle offsets.


*Stand alone SLM system*		*Dynascan configuration (single head and dual head)*		*MERLIN – Time-tagged, vessel mountable, Lidar system*

stands for Light Amplification by Stimulated Emission of Radiation. Laser class used by the LMS is 1 (FDA/IEC/EN60825-1), which is eye-safe, or 2 when the optional red pointer is available.

Notice that the driver has user-interface in order to control the laser unit system, which can be found in the Controller's Echosounder Settings dialog. For more information see Online setup below.

Driver Information

Driver	Renishaw SLM (XML)	Interface Type	Freebase/UDP	Driver Class Type	Freebase
UTC Driver	Yes	Input / Output	Input and Output	Executable	DrvLaser.exe MDL_SLM
Related Systems	Page: Laser Scanning - Renishaw SLM (XML) - 20 — Multibeam Echosounder
Related Pages

Decoding Notes

Communication between the driver and the SLM unit goes via a binary data stream, using Renishaw's own so-called SLM MDA072 format. This document does not describe the format description of these commands, messages and/or data packages.

Command messages to and data packets from the laser unit are broadcast via a UDP network connection.
This communication is based on a half-duplex UDP connection, which means that the driver is either in receive state, or in send state.
Due to the enormous amount of data to be expected, it is advisable to use a fast (at least 100Mb) network card. For more information see Network Setup below.

The driver will update QINSy with the decoded data after each full rotation of the laser head.

Upon decoding, the measured range is transformed to a travel time, using the speed of light as a constant.
Next to the pixel range and angle value, one other important attribute is decoded: the signal strength from the target's surface.

This signal strength is decoded and stored as Intensity and Quality indicator:

Intensity of the beam
The Intensity will be the signal strength and is expected to be in the range between 0 and 4095.

Quality Indicator of the beam
The Quality Indicator is a so-called normalized Intensity and this figure is always in the range of 0-255. Therefore the signal strength is divided by 16 to make it fit.

INPUT					Q = I / 16
File	EXT	Created	PIXEL	Intensity [0 - 4049]	Quality [0-255]
QINSy Database - Replay	*.DB	Online	Range/Angle
Processing Manager - Validator	*.QPD	Online, Replay	ENH (cm)
(since 8.10.2013.01.24.1)	*.QPD₂	Online, Replay	ENHIQ (cm)
QLOUD	*.PTS	Online, Replay	ENHIQ (cm)
Sounding Grid	*.GRD	Online, Replay, PM	ENH (cm)	(only when storing backscatter)
QLOUD	*.QTM	PM / QLOUD	ENH (cm)	depends on the import	depends on the import

The Intensity or Quality can be very useful to color-code the data using processing software like the Validator or QLOUD.

Notice that the original decoded value for the Intensity and Quality will be modified when the reported GPS Time/PPS pulse status is bad. For more information about this see Interfacing.

Interfacing Notes

Timing

By default, the driver will time-stamp the data when received at the UDP port.
When a full rotation is decoded, a delay time will be determined by dividing the rotation time (last arrival - first arrival) by the number of received packets. With this delay time, the arrival of each individual packet will be calculated.

However, due to UDP network characteristics in general, and because of latency inside the scanner, this will result in inaccurate timing.
Therefore timing via PPS/Time Synchronization pulse from GPS is highly recommended.

This means that your SLM unit must be interfaced with an external Time Synchronization pulse from a GPS receiver and a UTC time-tag message from the same GPS receiver. The required format of the time-tag message depends on the used GPS receiver, but normally this will be NMEA ZDA.

Notice that when working with a Dynascan system, Renishaw has already fully integrated GPS and PPS/Time Synchronization from factory.

It is important that QINSy is also interfaced with a Time Synchronization system, so all systems will operate in the same time frame.

The SLM unit automatically informs the driver if something was wrong with the Time Synchronization pulse and/or UTC time-tag message.
As soon as the driver receives a bad status about Time Synchronization timing, it will modify the original decoded values for the Intensity and Quality as follows:

Because the quality will always be 0 or 255 during periods with bad timing, you can easily spot those areas inside the Validator or QLOUD:
Use for color-coding the Quality and set the color scale range somewhere between 0 and 255. The under- and overflow color (default red and blue) will now represent the areas with bad timing.

Network Setup

All communication to and from the SLM laser unit goes via the onboard LAN network.

The exact LAN IP address of the laser unit should be provided by the manufacturer or your reseller. Normally Renishaw configures their SLM laser units with IP address 128.2.0.2xx.

The LAN IP address of your computer's network should be in the same range, except for the last digit.
This must be a unique number! Use for the subnet mask the values 255.255.255.0

Windows 7, 8.1 and 10:
Control Panel-Network and Sharing Center-Change adapter settings-Click right-mouse on Local Area Connection-Properties-Internet Protocol Version 4 (TCP/IPv4)-Properties...

Flowchart

General flowchart laser scanning

Database Setup

The driver is treated internally as a multibeam system, creating multibeam 'range' and 'angle' observations, therefore you will find the laser system drivers under category type Multibeam Echosounders.

Terminology 'Multibeam' versus 'Laser scanning'

Multibeam	Laser scanning
Ping	Scan (i.e. 360° around)
Footprint or Beam	Pixel or Pulse
Swath	Line or Scan

1. Edit System Wizard

Add a Multibeam Echosounder system to your template setup, and select driver "Laser Scanning - Renishaw Dynascan SLM".

The Port number must be the same as the configuration port of the scanner. The driver will communicate via this configuration port of the scanner. Ask the manufacturer or reseller what the exact port number should be. Normally it will be 30.

Also important is to enter the exact IP address of the scanner. Each scanner should have its own unique IP address. See Network Setup for more information.

Leave the maximum update rate at zero.

2. Multibeam Echosounder Parameters

Important are the Transducer Location (Node) and Mounting Angles (offsets) on the second wizard page.

As a rule of thumb, when you mount the laser unit backwards on your moving vehicle, and the marker on the unit is pointing upwards, then you may leave the Roll, the Pitch and the Heading offset zero.
A scanned profile as seen in a Raw Multibeam display should then be as in the real world.
As another example, if you mount the scanner backward looking, but with the marker pointing downwards, then you should already enter a Roll offset of 180°.

Set the Max. beams per ping value to 36000.
The actual number of beams will be variable, and depends for example on the used on-line settings and on the targets being scanned.

3. Echosounder Accuracy Parameters

You may leave all values on the third wizard page at their defaults.

4. Multibeam Echosounder Corrections

Important are the Range and Beam Angle Corrections on the last wizard page. These C-O settings are specific for Renishaw SLM laser units and can be measured by factory calibration, or determined after a calibration run.

Range Correction is the correction on the measured raw laser range. It can optionally be enabled if required, for Renishaw SLM a single correction for the entire range is sufficient.
It consists of two figures: a C-O which is the offset on the range, this should always be entered in meters, and a Scale Factor.
This figure will be multiplied with the range once the C-O has been added to it.
- Note: that if the Scale Factor is not used then leave it at 1.0.

Beam angle C-O is the offset on the rotation of the head.

Tilt angle C-O is the angle the laser is tilted from the rotation plane.

Beam Angle & Tilt Angle

Please contact the manufacturer for more information related to the beam angle and tilt angle.

Online

When on-line, the SLM laser unit can be controlled using the Controller.

Select Echosounder Settings, click on the Laser System icon, and select the 'Control' tab page:

Connected	In order to communicate with the scanner, you must make a network connection first. No This means that there is no UDP network connection between the driver and the laser unit. Yes Select this every time you go online with the Controller, in order to communicate with the scanner. If no connection could be made, a notification message will be displayed in the Events list. Under normal circumstances a connection will be established within a second. [ Set to Manual at startup ] Select this option (only once, and hit the Apply button) if you want to disable the 'Auto Connect' option. This means that every time you go online with the Controller, you must make a connection yourself by selecting 'Yes' from this list. [ Set to Auto Connect at startup ] Select this option (only once, and hit the Apply button) and the next time that you go online with the Controller, the driver will try to connect to the laser unit immediately.
Action	Selected action will be sent to the laser unit, immediately after hitting the Apply or OK button. You must be connected first in order to select an action. Notice that any selection will always revert back to [None], after each selected action. It is recommended to wait a moment after each action, until the status in the Event list is updated with a message, because it takes some time for the unit to handle each command (action). [None] This will be the selection after each action. Nothing will happen when you hit the Apply or OK button. Start Select this action in order to start scanning. Scanning should be started immediately after hitting the Apply or OK button, and the updated laser data should be visible e.g. in a Raw Multibeam Display. If you notice that nothing happens, check the notification messages in the Events list in order to pinpoint the problem. Stop Select this action in order to stop scanning. Scanning will be stopped immediately after hitting the Apply or OK button. The laser will also stop scanning automatically when you disconnect, or when going offline with the Controller.
Angle Resolution	Set the angle resolution, i.e. the angle increment between two consecutive pixels. The lowest resolution is 0.1° and the highest possible resolution will be 0.01°. (The latter scenario will result in a maximum of 36000 pixels per full scan). Notice that the behavior of High resolution may differ between firmware versions of the device.
Scan Speed (Hz)	Enter the rotation speed of laser head. Valid values: 1 - 10 Hz. Newer SLM units may support rotation speeds of up to 20 Hz. Check the messages in the Events list: after a successful connection it will report the maximum allowed scan speed. Notice that the frequency can have influence on the resulting angle resolution, see comments above.
Vertical Area Selection	Scanner head rotates 360° every line at the selected scan speed. 0° means looking down (opposite of the marker), 180° means looking up (marker direction), 90° looking starboard, 270° looking port. Decoded Angle Convention (When marker points upwards) Select the required scheme from the list. Schemes are defined in the Laser Device Settings XML File. Excluded data due to his setting will not be recorded!
Minimum Intensity	Set the minimum required intensity (signal strength). Valid values: 0 to 4095. Notice that blocked data due to this setting will not be recorded! This option may not be available in your setup. In that case all signal strength values will be accepted.
Maximum Intensity	Set the maximum allowed intensity (signal strength). Valid values: 0 to 4095. Notice that blocked data due to this setting will not be recorded! This option may not be available in your setup. In that case all signal strength values will be accepted.
Minimum Range	Set the minimum required range in meters. Valid values: 0 to 500 meters. Using this setting is recommended, but be careful: Blocked data due to this setting (i.e. all pixels less than this range) will not be recorded!
Maximum Range	Set the maximum allowed range in meters. Valid values: 0 to 500 meters. Using this setting is recommended, but be careful: Blocked data due to this setting (i.e. all pixels more than this range) will not be recorded!
Store Laser Location	If enabled, an additional pixel with zero range will be added to each line scan, in order to indicate the exact laser scanner location in the resulting point cloud. This extra pixel will always have beam number 0, and its intensity and quality values will be zero.
Use PPS	This setting is highly recommended, in order to use exact time stamping of the laser data. When enabled, the laser unit must receive a valid PPS pulse from an external GPS receiver and UTC time-tag message. See Timing for more information.
Capture Raw Data	Enable this option if you want to store the raw binary data stream coming straight from the unit to a log file on disk. This may be useful for debugging purposes, or to load the data into other software. This binary log file will be located in the current project's LogFile folder and the naming convention will be <System Name> - DD-MM-YYYY - <Sequence>.bin. The sequence number is incremented after every Start/Stop scanning action. Please note that this binary file is of no use for QINSy, and it may effect the online performance because of the extra hard disk activity. This option may not be available in your setup. In that case no raw data will be captured.

Additional Information

The SLM has the following features and limitations:

The range resolution will be centimeters, with a maximum of 150 meters (500 feet), or 500 meters (1500 feet).
The angle resolution will be 0.1° or 0.01° (user-definable).
The number of scans per second will be between 1 and 10 Hz. (user-definable)
Newer SLM units may support rotation speeds of up to 20 Hz.

We have seen that it shuts down when you go above a certain spin-rate. In that case check if you have a sufficient power supply.
The maximum expected number of beams (pixels) per second will be 36000 (theoretically).
The actual number of beams depends on the on-line used settings, like range mask, vertical angle mask, intensity mask, etc.
(see Online Setup for more information)

Problems

If you experience problems using your laser scanner in combination with this driver, or if you need additional information or support, please attach the daily laser log-file when submitting your JIRA support ticket.

The most commonly reported problem is that network data is blocked by the Windows Firewall. When this happens you may see that data does come in using other utilities (like the IO Tester or the manufacturer's own software), but that the Qinsy driver does not accept any data.

The following (Windows 7) steps may solve this:

Go offline, open the Control Panel (Start menu, Settings, Control Panel)
Select Windows Firewall (System and Security)
Select Advanced Settings (Upper left corner)
Select Inbound Rules, highlight all 'Driver for Laser Scanning' entries and delete them using the right mouse popup menu (or Del key)
If you now go online, the Windows Security Alert message will pop up: It is important to check all three check boxes!

Another possible problem could be that your computer has more than one network cards installed (e.g. LAN and WIFI), but within the same sub-net mask range (255.255.255.0). It is recommended to make the first three digits unique for each network card IP address.
You may check the daily laser log-file, it will show the IP addresses for all available network adapters and indicates which one the driver will use.

Please check that the driver is using the correct one.

Daily Laser Log File

All user actions are logged in a daily laser log file. You will find this file in the current project's LogFiles folder.
The filename convention for this ASCII log-file is <System Name> DD-MM-YYYY.log.

Notice that all time stamps in this log file are by default in UTC.
An advanced user may change this to local time zone (LTZ) by changing the registry key:

HKEY_CURRENT_USER\Software\QPS\QINSy\8.1\Drivers\DrvLaser\Settings\TimeLogFileUtc value from 1 to 0.