A Technical Guide: Drone LiDAR Vs. Photogrammetry

Introduction

GIS (Geographic Information System) is gaining momentum in the present scenario. Photogrammetry& LiDAR (Light Detection And Ranging) technologies are latest technologies revolutionizing the way we are working. In this article, let us dig through the circumstances to determine the right kind of sensors to use.

UAVs (Unmanned Aerial Vehicle) promises cheap and easy survey’s, but yes, there is something more that they can provide. To get the results that suit your requirements, you probably have to educate yourself about the sensors the UAVs uses to capture the data. You will also have to educate yourself about LiDAR and Photogrammetry.

Here is an informative guide that takes you on a deep dive to decide when it is best to use photogrammetry, LiDAR, or both when you are surveying with your UAV.

Apply UAV LiDAR when…

You want to map below the tree shade, mine sites conveyors and other various obstructions.

Reason: Photogrammetry faces difficulty while generating elevation models in areas where objects block the ground. The traditional photogrammetry tends to do mistake while creating a digital elevation map. When calculating elevation for a point on the earth, Photogrammetry requires two images that can see that point. If a tree is interfering the position, it may show up in one picture but not the other. It probably confuses the automation algorithms that match the images. As a result, the output is a noisy elevation model.
What’s the scenario of Modern Photogrammetry?

Well, it worsens the problem. Once the algorithm is developed, photogrammetry could generate “very dense point clouds, which are often with a spacing factor or two or are larger than the resolution images.” This is called as Dense Image Matching (DIM) which creates surface models rather than actual elevation maps.
In other words, Photogrammetry is not an ideal technology for mapping elevations when the ground isn’t clear from all angles.

Apply UAV LiDAR When…

You are modeling smaller, narrow objects like pipes, sharp-edged features (roof edges), and field of rocks.Reason: LiDAR Models the object excellently because a single ray from the scanner measures each point in the cloud. Whereas, in Photogrammetry, the model doesn’t correspond to the object as well as modern photogrammetry makes rough estimations and then smooth’s the model out to remove noise.
Thus, this makes modern photogrammetry a tough sell for modeling the tinier objects precisely.
Now let’s have a look at when to use Photogrammetry.

Apply UAV Photogrammetry when…

You are imaging bare earth mine sites, groundwork projects, other areas that are not occupied by trees as well as buildings.Reason: Drones are indeed cheaper, lighter as well as faster in working. If the work you want to do doesn’t require LiDAR, then attaching a camera to your UAV will save a lot of money and time as well.

Apply UAV Photogrammetry when…

You are performing a small mapping project, and photogrammetry data will fulfill your requirements.Reason: It is financially not feasible to mobilize a manned aircraft for a small-site mapping project work. Whereas, a UAV is small to handle by a single surveyor and operate it in the field without any help.

Apply LiDAR as well Photogrammetry when…

You are about to perform modeling that requires LiDAR.Reason: The high-resolution data can be a bit tough to collect with aerial LiDAR. This means one needs something extra to get the data with imagery. The ideal scenario is to use imagery for context and LiDAR for obtaining the 3D Component.
While the cameras are inexpensive and offer a great value that there aren’t many facts to ignore them out of the UAV sensor package.

Use What Makes Sense For Your Business

LiDAR and Photogrammetry are both impactful and full of potential when utilizing in right way. The point is finding the right sensor for your requirement.
In a more straightforward form, if you want to map clean stockpile yards of fine materials, then photogrammetry is the cost-effective solution. On the other hand, for the projects that require modeling, then LiDAR is a perfect choice.

The beginning of the new era of 3D Scanning (Solid-State LiDAR)

Well, the technology will see a sharp shift in coming years. The reason is Focal Plane Array (FPA) LiDAR also known as Flash LiDAR or Solid-State LiDAR.
Here is the easiest way to understand how FPA works. Imagine it as a digital camera taking pictures. Once LiDAR frames a shot, instead of taking pictures, a single laser flash and the entire scene gets captured by an array of detectors.
The FPA LiDARs are perfect for drones because they are cheaper, smaller as well as lighter and are more geometrically exact than the existing LiDAR units.
Thus, the demand for FPA LiDARs is going to skyrocket in the next few years. Stay tuned till then!

Source: https://blog.nibt.education/2018/03/a-technical-guide-drone-lidar-vs-photogrammetry/