Real-world accuracy of Drone-based LiDAR
How accurate is drone LiDAR?
This is the most common question we hear from our lidar customers here at Candrone, and it’s a good one. Lidar systems are complex, their spec sheets can be as well. Join us over the next couple of months to break down the jargon in a short-series of blogs!
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Today we’re going to look at Beam Divergence! What is it, and why does it matter?
Beam divergence can best be visualized like a flashlight beam - starting narrow at the light source, and widening at a constant rate as distance increases. Every laser pulse emitted from a lidar sensor diverges, so you end up with a lot of the pulses overlapping each other when they hit the target. Imagine shining several flashlights at the same area of a wall.
The further you get away from the target, the wider the beam gets. This creates more and more overlap you have between pulses. In a very rough way, you can think of the beam divergence as a representation of the resolution or sharpness of your model.
Why should we care about this?
Well, it’s one of the key specs defining how much noise your model will have.
High beam divergence = Lower resolution = Fuzzy corners on small or sharply defined features.
[insert cross section of v70 data]
For example, the spec sheet above is for the Livox Avia - this is the lidar sensor used in DJI’s new L1 lidar, GreenValley International’s LIAIR V70, amongst others.
The beam divergence is quoted as 0.28° by 0.03° this means at 100m distance you’re getting an oval-shaped beam splash 49cm long by 5cm wide.
Below is a comparison of what a staircase looks like with low vs high beam divergence.
High beam divergence = Lower resolution = Fuzzy corners on small or sharply defined features such as stairs. Below is a scan using the GVI LiAir V70 to scan a stairwell at 80m elevation. Try picking out the step edges!
The Teledyne CL360 lidar sensor has a beam divergence of 0.3 milradians. At 100m that’s a circular splash only 3cm in diameter.
There’s a big difference in price between these two sensors, and this is reflected in the precision of the point clouds you’ll get from each. Higher performance lidar sensors are usually larger and heavier though, so flight times and coverage areas will suffer. Bigger isn’t always better - it’s important to determine which lidar system will suit the type of mapping you’ll be doing most.
Point clouds from the Teledyne will show smaller features like kerbs, retaining walls, building edges and street furniture in sharper detail - there will be less point cloud noise around these defined features and it’ll be easier to extract accurate vectors.
The reverse is also applicable - if you’re mapping natural surface features then having low beam divergence isn’t as important - the lower cost unit will likely fit your needs and provide a higher productivity solution.
A good rule of thumb is - if the beam splash is larger than the feature, the feature probably won’t be very easily definable in the point cloud.
So what will be the best lidar sensor for your needs?
The lidar specialists at Candrone can help you make this decision. We offer extensive pre and after sales support to help you make the right decision, and get the most from your gear.
Give us a call today, or join our mailing list to get the scoop on our latest blogs, training, and tips!
Next blog will be all about returns - see you next time!