Boresighting Your LiDAR Laser

This article outlines how to boresight your R2A or R360 laser for increased accuracy.

1. Capture a dataset

  • Use a tight double gridded flight plan over a building or set of buildings. The peak of the roofs will be used to align the lasers.
  • Speed: 5 m/s (11 mph)
  • Height: 50 m or 165 ft
  • Camera trigger 5 seconds (See Calibrate the LiDAR RGB Camera  if we wish to use this mission to calibrate your camera too)

2. Process the trajectory in PCMaster and then create a slice.

  • Right click and choose "Color by Intensity" to easier view your data. 
  • Move the focus point to the roof - sometimes edges are easier to see the peak. This will vary based on your dataset. 
  • Just Shift+Control and zoom in closer to the peak of the roof
  • Create a slice which is parallel with your flight trajectory to calibrate Yaw and Pitch. 
  • Once the focus point is near the peak of the roof, right click and choose "Start slicing at focus point"
  • Hold control and move the focus point carefully along the peak of the roof to create a small slice (see example below)
  • Right click and choose "Finish slicing" 
  • This will be repeated later, but this step helps clarify the area you will be using in later steps

Tips for Maneuvering

Left click and drag the mouse: rotate the dataset

Hold Shift and left click: rotate the dataset

Hold Control and left click: move the focus point in PCMaster

Hold Shift and Control and left click: move the dataset up or down - this helps get closer to the roof

3. Color by Laser

  • Right click and choose "Color by Laser".
  • This will allow you to see a different color for each laser 
  • The R2A has 6 lasers the R360 has 32. 

4. Create Paths

  • Go to Paths and remove the original path
  • Go back to the dataset and create a selection at the beginning and end of each flight line over your roof
  • Choose slices all in one direction

5.  Adjust Values

  • In the toolbar at the top of PCMaster, go to Linear Offset and confirm the values:
    • R2A (0, 0.0480, -0.0730) 
    • R360 (0, 0.065,0)

6. Reset the Angular Offsets.

  • Make note of your existing offsets
  • Click on IMU-LiDAR Angular Offsets and reset the Yaw, Pitch, Roll values to zero. 

6. Calibrate the Yaw value

  • Isolate the paths which are moving in the same direction. i.e. all paths flying from the North to the South in this example would be the green and the brown
  • To confirm the direction, you can zoom in closely on the trajectory and see the line is made up of small arrows indicating the direction of flight.
  • Click on Lasers and uncheck the display column for the green and brown path.
  • Go to the slice and click the up and down button for the Yaw value in Angular Offsets until the slice is aligned vertically. 
  • You can come back and refine this if you wish after adjusting Roll.

roof slice

 

7. Calibrate the Pitch value

  • To edit the Pitch value, isolate the paths which are moving in the opposite direction of the Yaw paths.
  • Click on Lasers and check the green and blue path only in the display column.
  • Recreate slice and click the up and down button for the Pitch value in Angular Offsets until the slice is aligned vertically. They don't have to be perfectly converged, just aligned to one another, as below. 
  • You can come back and refine this if you wish after adjusting Roll.

pitch

8. Calibrate the Roll value

Create a slice which is perpendicular with your flight trajectory to calibrate Roll. 

  • Recreate the slice and click the up and down button for the Roll value in Angular Offsets until the slice is aligned horizontally.  

 Before:

before roll

After:

after roll

  • At any point you can go back and adjust Yaw, Pitch, and Roll. Sometimes you may need to adjust a few times to get it as tight as possible. 

10. Verify the Yaw and Pitch values 

Once the Yaw and Pitch values are added. Create a slice which is parallel to your flight trajectory to verify your Yaw and Pitch values. If small adjustments are needed for Yaw and Pitch, add them accordingly to the slice until the slice is aligned vertically. 

11. Verify the Roll values

Once the Roll values are added. Create a slice which is perpendicular to your flight trajectory to verify your Roll values. If small adjustments are needed for Roll, add them accordingly to the slice until the slice is aligned vertically.  

12. Adjust Laser Values

  • Click on Cloud Filter
  • Click Rotation Angle and click the check box. For the values: R360 225-315 and R2A 237-303
  • Select all of your paths
  • Select a roof slice, try to use the steepest one possible
  • Open Lasers in the toolbar
  • Right click the dataset and choose "Color by Laser"
  • The R360 has 32 lasers and the R2A has 6. For the R360, use groups of 4 lasers at a time. For the R2A this is less important but you can use 2 to 3 at a time. 
  • Manually adjust the Azimuth and Elevation and determine if the points improve from the adjustment. Sometimes no adjustment is needed.
  • The goal is to minimize the thickness of the points and maintain the roofs shape
    lasers r360
  • It is easier to move the points outward and then back inward to ensure they're as tight as possible. 
  • This process may take sometime but it is important. 
  • Repeat each group of 4 (on the r360) until you complete them all
  • Turn on all the lasers and verify the point cloud is tighter than when you started. 

Before Laser Adjustment: 

before laser

After Laser Adjustment:

after laser

When you are done with all lasers, go back and check other roof slices areas to ensure they look good. Before and after screenshots will help you verify!

 

13.  Storing the Computed Values

 

Saving your newly computed laser boresighting values in the PCMaster Project file  will allow you to load these values as standard onto your R2A or R360 using the web interface. They will be recorded in the files on the device when you are capturing data. When you create a new PCMaster Project, these values will also then be automatically loaded there.

To store the desired values:

  1. Save a PCMaster file to your USB Drive. It is called ppk.pcmp
  2. Open the web interface
  3. Go to the Settings -> Boresight
  4. Click “Read from PCMaster project”
  5. Browse for the PCMaster Project file and select it

Now the computer values will be extracted from the file and stored in the LiDAR Payload non-volatile memory.

 

 

Have more questions about this topic? Visit community.rockrobotic.com to create a post to ask questions and connect with other community members as well as the ROCK Support Team.