Acquire Point Cloud Data with Absolute Coordinate
There are two ways to obtain a point cloud with absolute coordinates: through existing ground control points, or through the RTK module. The former suits a variety of indoor and outdoor scenes; the latter requires good RTK signal outdoors.
Through Existing Ground Control Points (GCP)
By collecting existing ground control points with the device, the scanned point cloud can be coordinate-converted while also improving point cloud accuracy.
Note
The number of control points in the survey area depends on the accuracy requirements, and they should be laid out evenly. To ensure the subsequent coordinate conversion, a single scan needs at least 3 reasonably distributed control points. The more high-accuracy control points and the more evenly they are distributed, the higher the accuracy.
1. Device installation
The components used include the Lixel L2 Pro handheld scanner, battery, and GCP Collection Base. The installation is shown below:
2. Field work
Field survey and planning
If a topographic map of the survey area is available, design the control points based on it and refine the design during the on-site survey. If there is no such map, design based on the on-site environment.
Control points should be distributed as reasonably as possible, evenly across the survey area, with the spacing between them kept within 100 m. To ensure the coordinate conversion in post-processing, there should be at least 3 control points, and they must not lie on the same line. Plan a reasonable scan route based on the control point distribution and the scan environment.
Start scanning
Turn on the scanner and start scanning through LixelGO or the device itself. For detailed steps, see the power-on and capture workflow.
Add external control points during scanning
When passing a control point during scanning, align the pointed corners around the scanner's control point base with the control point location, then add the control point in LixelGO or via the shortcut button. You can use a standard control point target nail or a standard control point target sheet.
Tap "Control Point Mode" on the left side of the screen.
[GCP] Tap "+" on the left side of the screen to add a control point.
Enter the control point number and tap OK. When "The control point was added successfully" pops up, the control point has been collected.
Note the name and order of the control points recorded in LixelGO when marking them. During later processing in LixelStudio, make sure the imported control point file names correspond one-to-one with the control point names recorded in the device.
If a duplicate control point name is added, LixelGO shows a pop-up reminder; make your choice based on the actual situation.
In the "Control Point List" on the left, you can view the collected control points and delete them. Tap the delete button to the right of a control point to remove it.
[POI] Tap "+" on the left side of the screen to add a point.
Stop scanning
Tap the red stop-record button on the right side of the screen. The device flashes green quickly; once scanning ends, the device turns solid green. You can then power off or start a second scan.
3. Office work: data processing
See the LixelStudio product manual.
Through the RTK Module
By using the RTK accessory, absolute coordinate information can be obtained directly during capture, which also improves the overall accuracy of the point cloud.
Note
For the best results, use this mode for scanning outdoors where the RTK signal is good.
1. Device installation
The components used include the Lixel L2 Pro, battery, base bracket, and either a survey RTK or a standard RTK.
The installation is shown below:
Note
- The RTK module indicator light has three colors: blue, green, and red.
- Red: RTK not connected; Blue: RTK connected, not fixed; Green: RTK connected and has a fixed solution.
2. Field work
Scan route planning
Plan the scan route reasonably based on the on-site environment, keeping the RTK signal good along the route as much as possible. To ensure post-processing accuracy, keep any continuous RTK signal loss or non-fixed sections along the route within 100 m.
Connect the device
Turn on the scanner and connect to it through LixelGO. For detailed steps, see the power-on and capture workflow.
RTK account settings
Enter the device screen, tap RTK settings (the satellite icon button) to enter RTK settings. Three account configuration methods are currently provided: Qianxun SI, China Mobile, and Custom, which you can configure based on your situation. The custom settings are as follows:
Set the source ellipsoid to WGS84 or CGCS2000 to directly output an absolute-coordinate point cloud. Note: currently only WGS84: UTM 3-degree zone, and CGCS2000: Gauss-Kruger 3-degree zone are supported, with the geodetic height as elevation.
Qianxun SI and China Mobile: log in by entering the corresponding account and password.
When you have one or more frequently used accounts, you can use the Save button to store the RTK account information in the LixelGO app cache.
How to use:
- Enter the RTK account information: host, port, source node, etc.
- Tap the Save button. A dialog appears to select the configuration item to save; tap Save, and the RTK account information is saved in the LixelGO app cache.
- Tap the Edit button to change the name of a configuration item; after saving, the RTK account configuration name is changed.
- The drop-down list shows the saved RTK account configuration items.
Note
- Currently Qianxun SI, China Mobile, and Custom RTK are supported. Using Custom RTK requires the RTK data format to be a common format, otherwise it will not work properly.
- The device automatically records the RTK account information the first time it is set, and logs in automatically afterward.
- Changing the RTK coordinate system takes about 5 minutes; it is recommended to start work 5 minutes after the change.
- The RTK accessory can currently obtain absolute coordinate information in WGS84, CGCS2000, and ITRF2008, with the geodetic height as the elevation system.
RTK advanced settings
The L2 Pro RTK has three GNSS modes.
| GNSS Mode Settings | Definition | Description |
|---|---|---|
| RTK | The RTK module uses the RTK function, receiving differential data and recording it into the project file | On the startup page, select RTK mode according to the actual project requirements. In LixelStudio, the RTK module is required for project processing. |
| PPK | The RTK module uses the PPK function, receiving raw satellite data and recording it into the project file | On the startup page, select PPK mode according to the actual project requirements. In LixelStudio, the PPK module is required for project processing. |
| DJI | The device obtains the RTK data provided by the aircraft and records it into the project | On the startup page, select DJI mode according to the actual project requirements. In LixelStudio, the RTK module is required for project processing. For details, see the drone accessory section of the manual. |
The L2 Pro has three RTK types.
| RTK Type Settings | Definition | Description |
|---|---|---|
| Standard RTK | The device uses the parameters of the standard RTK | On the startup page, correctly select the RTK type mounted on the device. |
| Survey RTK | The device uses the parameters of the survey RTK | On the startup page, correctly select the RTK type mounted on the device. |
| Aerial RTK | The device uses the parameters of the XGRIDS drone accessory | On the startup page, correctly select the RTK type mounted on the device. |
Satellite system settings
In RTK advanced settings, you can personalize the satellite system selection. Single selection, multiple selection, and select-all are supported.
Prerequisites: 1. firmware version 2.3.0 or above; 2. RTK is connected.
Options
- When you enter RTK advanced settings, the satellite system settings in the device are read and displayed automatically.
- Single selection, multiple selection, and select-all are supported.
- After checking your selection, tap Set; it takes effect immediately once the setting succeeds.
Start scanning
In RTK mode, wait for the RTK module indicator to turn green and for the RTK signal in LixelGO to show Fixed, and only then pick up the scanner to start scanning.
Precautions
RTK mode only supports outdoor scenes with RTK signal; RTK cannot obtain a fixed solution indoors.
When the RTK has a fixed solution, the RTK module indicator turns green. When it is blue, watch the number of satellites.
Only start work when the satellite status in LixelGO is Fixed, not NONE, Float, or Single.
To ensure accuracy, keep the device in the fixed-solution state for most of the capture. There must be more than 100 valid RTK data points for the coordinate conversion to work properly in LixelStudio.
When capturing, keep the scanner as vertical as possible. While walking, the scanner tilt generally should not exceed 20°. In special cases, such as scanning the ground of a small space or a ground target, the tilt must not exceed 30°. Refer to this icon and adjust the device posture in real time, trying to avoid the "Please return the device to an upright posture" prompt.
- Pay attention to the scan spatial range and ensure that, with the satellite status "Fixed", the walking range is over 10 m. Otherwise LixelStudio will not be able to perform post-processing.
Stop scanning
Tap the red stop-record button on the right side of the screen. The device flashes green quickly; once scanning ends, the device turns solid green. You can then power off or start a second scan.
3. Office work: data processing
See the LixelStudio user manual.