GEO SLAM ZEB Locate LiDAR Scanner User Guide

GEO SLAM ZEB Locate LiDAR Scanner

Introduction

ZEB Locate is an add on to the existing backpack-mounted ZEB Horizon and has been developed and tested on the Trimble DA1 antenna. However, other GNSS receivers are supported as well. This user guide uses the Trimble DA1 antenna, which requires a subscription to the Trimble Correction Hub (both to be purchased independently of GeoSLAM). GNSS data is logged to an Android device via USB connector. Catalyst subscription level “Precision” provides accuracy level of 1 – 2cm. Positional accuracy is displayed in the Catalyst Mobile manager app on Android device.

How Zeb Locate Works

The workflow below (Figure 1) describes ZEB Locate operation in five steps.

1. Step 1. Data capture
2. Step 2. Copy data to computer
3. Step 3. Process SLAM data in GeoSLAM HUB
4. Step 4. Process SLAM data and GPS data in ZEB Locate Processor
5. Step 5. Georeferenced point cloud

Capture Data

This section describes how to prepare hardware, configure the software and scan with ZEB Locate system.

Assemble Backpack
GeoSLAM Zeb Locate solution contains ZEB Horizon, backpack frame, ZEB Locate Processor and our data logging app for Catalyst data capture. If users have ZEB Discovery, the same backpack can be used for Locate by simply swapping the camera with GNSS antenna.

Zeb Horizon to ZEB Locate
To assemble backpack:

• Loosen clamp levers on backpack harness frame by pulling outwards.
• Insert backpack pole assembly into clamp.
• Tighten clamp levers by pushing inwards.
•  Attach Scanner and Datalogger onto harness using V-lock mechanism and connect with the provided Horizon’s cable (Figure 3).
•  Attach battery
• Screw Trimble Catalyst DA1 antenna on the top of the post’s 5/8″ thread adapter.

There is an optional magnetic mount for your phone that can be placed on the backpack post. Figure 2 shows the assembled ZEB Locate. The cables and connections should be kept neat and away from sensors to avoid getting caught or tangled.
The Trimble Catalyst has a hardwired micro-USB out as its main cable and comes with USB-C adapter. There is a second micro-USB port at the bottom of the DA1 antenna for external power.

Zeb Discovery to Zeb Locate
ZEB Discovery’s backpack frame can be used interchangeably with Locate or Discovery. NCTech Pulsar+ camera needs to be carefully removed from the top of the post.

•  Remove the 2 orange brackets that secure the camera to the post, so you can easily switch back to Zeb Discovery later (Figure 5).
• Remove the camera’s power cable and remove the power adapter from the backpack.
•  Add 5/8″ adapter into the top of the post (Figure 4). It can be removed from the post with a plier or wedge when switching back to Discovery.

Follow instructions for Zeb Horizon to Zeb Locate from the  Select Catalyst Service
Various subscription levels are available based on the accuracy required for the survey or amount of usage (Figure 6).

Catalyst system (Figure 7) utilizes a range of correction sources and further info on the Catalyst system and subscription levels can be found here: https://geospatial.trimble.com/catalyst

Catalyst Precision Subscription

Data or Wi-Fi is not needed to check the license.

Catalyst on Demand

Mobile connection is needed to check account as it provides hourly packages. Multiple users can pull from one On-Demand pool.

Android App Download and Configuration
Two apps and one service are required on the Android device. The Trimble Mobile Manager, Trimble Catalyst Service and Geoslam_Locate app from GeoSLAM. Android settings must be carefully configured to ensure proper communication between hardware and software.

Downloads
From the Playstore, download (Figure 8):

•  Trimble Mobile Manager (TMM)
• Trimble Catalyst Service.

As one is an app and the other is the service, you will only see Trimble Mobile Manager as an Application, but Trimble Catalyst Service is present from settings menus. From GeoSLAM (not available on Playstore), install

• GeoSLAM_locate.apk

Trimble Mobile Manager
Combined with the Catalyst service, this application handles your subscription, provides read outs of GNSS status, and communicates the signal readouts to your android device in your assigned format. Home Page: Landing page for TMM app. This page provides accuracy read, overview of account status, and the toggles to connect to Catalyst. If you are using on demand, this is where you can start a session. Position Source: Receiver type is assigned in here, as well as a read of device compatibility and status (Figure 9).

Keep software up to date. Status: This page provides greater detail of location and accuracy, as well as information on satellites and stations that are helping to find your position. GNSS Configuration: Corrections and outputs are controlled in this menu. Select Reference Frame WGS84 and EGM96 for Geoid (Figure 10).
Catalyst: Checks Status of Receiver. Hardware Licenses: Checks Trimble Account for subscription info. Application Settings: Select metres for units. Share location MUST be enabled in order to correct location to stream to Geoslam_locate app (Figure 11).
For this to work properly, you may need to enable ‘Mock Location’ found within the Android Developer mode. You will also want to assure that TMM is the only location source.

Android Location Settings
To enable Developer Options, open the Settings screen, scroll to the bottom, and tap About phone. Find build number at the bottom of the About screen and:

•  Tap the “Build number” field seven times to enable developer options.
• Switch Developer options on.
•  Scroll down and set Trimble Mobile Manager as the mock location app.
•  Additionally, force full GNSS.
•  Exit Developer Options.

Search for location in settings. Location needs to be on, but all location services within need to be off or disabled; Wi-Fi and BT Accuracy improvements should be disabled (Figure 12).

GeoSLAM GPS Logger .apk
Functions: Our GPS logger is essentially a virtual controller with 3 functions:

•  Start logging
• Stop logging
•  Generate CSV file

Start and stop functions are available in the app interface. The .csv that is produced named name ‘catalyst_#############’ can be found in the androidPC\SamsungGalaxyS7\Phone\Android\data\com.geoslam.trimble_catayst_logger_acc\files
Settings and Configuration: The app functions require permission to utilize location and file storage. To assure that the correct location source is being written without interruption or default to the android device location, allow for background data and background activity (Figure 13).

Logged accuracy precision can be checked by examining the recorded CSV. If GPS is recorded from the phone instead of the Catalyst, the accuracy of the collected data will be low (Figure 14).

Figure 14: Accuracy difference in recorded Catalyst CSV file. First file shows low accuracies as phone GPS was used instead of Catalysts (second file)

Mobile Scanning with Zeb Locate
ZEB Locate like other ZEB family products keeps the core value of simplicity for data capture and processing.

Order of Operations
The Zeb Horizon scanner functions the same as listed in the User Guide and Quick Start Guide. Zeb Locate procedures are carried out alongside the standard scan process.

1.  Set the ZEB Locate backpack down in a good starting position. This should be on a stable, level area with open skies to receive as much GNSS data as possible. The scanner should be facing features that the SLAM algorithm can use for a good solution.
2. Check cables and connect the Android device to the DA1 antenna with USB Micro-B. Keep the Android device at hand to check positional accuracy during the scan if needed.
3. First run the Trimble Mobile Manager app and connect to the service (Figure 15).
4. Positional information will be displayed on the Home screen in Lat, Long, Height with an accuracy estimation. This estimate of positional error will reduce as more data is received. In open skies this will take approx. 2mins to achieve ‘Precision’ level accuracy. In tests this has regularly reported <3cm. The subscription expiry date is also displayed.The Settings button will allow for a configuration check which should read as follows:

•  Check that the Ref Frame is WGS84 with the EGM’96 geoid (Figure 16).
•  The Status page has further information about horizontal and vertical precision (Figure 17):
• 4Do not move the system until a good positional accuracy is reported.
• Once this has been achieved start the ZEB Horizon scanner as for normal operations. ZEB Locate utilizes our SLAM algorithm and users need to follow Horizon’s best capture practice. ZEB Locate will allow you to capture GNSS restricted environments (mind antenna height) and georeference the pointcloud data without decreasing pointcloud accuracy in those places. A sufficient outdoor, good GNSS capture is required to georeferenced such data correctly.
• When the ZEB Horizon scanner is running (scanner head rotating) and we have a good GNSS positional ‘fix’ start data logging in the GeoSLAM GPS Logger (Trimble Catalyst Logger) app (Figure 19). Minimum ZEB Locate recording is 60s. First 60s of any project also need highly accurate GNSS data (< 0.1m).
• Only positional info is displayed here in Lat, Long decimal degrees.
• After the scan return to start position for a closed loop survey. This should be an open sky area and set the ZEB Locate down on a stable, level surface.
• After a few seconds stop the ZEB Horizon scan as normal with FNC button and then stop GNSS logging in the GeoSLAM GPS Logger app.
•  Download GeoSLAM scanner data as normal from the data logger via USB.
•  Download Catalyst data from internal Android device memory > This PC\Samsung Galaxy> S7\Phone\Android\data\com.geoslam.trimble_catayst_loggeracc\files Files named ‘catalyst#############’ > Time/Heading/Lat/Long/Elevation/Accuracy CSV.

Using other GNSS receivers
ZEB Locate support variety of GNSS receivers. ZEB Locate Processor accepts 1Hz of GPS data in the following format (Figure 20):

When using other GNSS receivers that Catalyst, they need to be configured to one of the formats above.

Copy Data to Computer
Import data to your workstation that runs GeoSLAM HUB software.

Software and Licensing
The Zeb Locate Solution includes

•  GeoSLAM Hub
• Zeb Locate Processor
• Follow the installation instructions found in the HUB User Manual and follow the ZEB Locate installer wizard. After installation, ZEB Locate Processor will ask you to import the calibration XML file. This file contains lever arm offsets and it is delivered with the software. Users can also define the offsets manually. ZEB Locate activation will be added to your existing GeoSLAM HUB license. Contact [email protected] with your HUB activation key in order to enable ZEB Locate Processor. Once activated, refresh entitlements in HUB.

Data Transfer
Download .geoslam file from Data Logger via USB (Figure 21). Transfer .csv from Android to PC without altering formatting.

Process Data in HUB
Horizon data can be dragged and dropped into HUB for SLAM processing. Consider adjusting processing settings if necessary. Once processed two files are required for ZEB Locate Processor:

• Pointcloud Trajectory. From HUB Export > Trajectories > trajectories with quaternions (TXT)
• Pointcloud (LAS or LAZ). Consider smoothing and spatial decimation (Figure 22).

Process Data in Locate
ZEB Locate Processor aligns Horizon’s trajectory with GNSS trajectory and transforms the pointcloud into georeferenced LAZ.

System Settings

• Select correct GPS data type format
• Select required coordinate system
• Save changes

Calibration
The CALIBRATION tab contains XYZ Lever Arm between Horizon and the top of the backpack post. Those Factory Defaults are also saved with the provided XML file that users can load during the software installation (Figure 24).

Catalyst DA1 antenna phase center offset is already taken into account during data logging (Figure 25).

For any other Locate installation, please contact [email protected] for correct Lever Arm measurements. Antenna height and offset to the ZEB Horizon scanner are accounted for in the ZEB Locate Processor.

Process

ZEB Locate Processor requires the following data:

1. ZEB Trajectory (txt file with quaternions exported from GeoSLAM HUB). Example 2020-03-12_13-22-44_results_traj.txt
2. GPS Trajectory (Catalyst CSV, NMEA GGA & GST or GGA only).
3. Point Cloud (.las or .laz file exported from GeoSLAM HUB)

To process the data, load in GPS trajectory and Plot GPS Accuracy Plot (Figure 26).

Filter Threshold can be adjusted based on the plotted results. “Apply Filter” option will remove the data below the specified threshold. GPS Accuracy Threshold will help to exclude poor GPS data from processing (Figure 27).

After the accuracy threshold has been selected, add ZEB Trajectory, and press Process Data (Figure 28).

GPS and ZEB Horizon trajectory should be well aligned (Figure 29).

Trajectory Registration will show RMS error. If satisfied with results, add pointcloud data andhit the ‘Process Data’ button again and the software will begin the georeferencing alignment (Figure 30).

The process runs through three main stages (Figure 31).

The process automatically registers the scan data to the GPS data (Figure 32).

When the process is complete you will see this message:

And after clicking OK a plot showing the positional difference between the SLAM trajectory calculated in GeoSLAM HUB and the GNSS positions will be displayed (Figure 34).

Georeferenced Pointcloud
Resulting georeferenced pointcloud will be exported to the folder containing the input pointcloud and will be named ‘Registered_PointCloud.las/laz’. The pointcloud will be exported in selected coordinate system. If a file of the same name already exists in this folder you will see an option to overwrite or choose new output location.

References

• Trimble Catalyst | Trimble Geospatial

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