Choosing the right drone survey

Key takeaways

Think less about the drone and more about what technology is needed.

Access is not a factor for a drone. A drone only needs a take off and landing point combined with ground control, within any legal restrictions.

Your two main options in selecting technology for land surveying, include LiDAR and photogrammetry.

LiDAR is the right choice for heavily vegetated areas to see what's underneath.

Photogrammetry is a better solution for hardscape land, in a city or built up areas.

Stop thinking about the drone. Start thinking about the technology.

When clients come to Engineers With Drones asking about drone surveys, the question they almost always lead with is about the drone itself - which model, which sensor, what specification. It is a reasonable thing to ask, but it is the wrong place to start. "You never want to be thinking about the drone," says Bob Foley. "You always want to be thinking about the technology to use."

That shift in thinking changes everything about how you approach a project. The drone is just the delivery mechanism. What actually determines the quality and usefulness of your survey data is the technology it carries - and for land surveying, there are two options: LiDAR and photogrammetry.

Access is almost never the issue

Before getting into technology selection, it is worth clearing up a common misconception: that difficult terrain or restricted access limits what a drone can do. In practice, it rarely does. "The drone doesn't care about access except for things like airports and whatnot," Bob explains. "So long as you have a takeoff and landing point and you can access a sufficient amount of points to put down some ground control, then the drone will go wherever it likes, wherever it's legally allowed to go. So that's not a factor."

That means a steep valley, a remote hillside, a densely wooded site or an active industrial facility are all workable. The conversation very quickly moves from "can we get there?" to "what do we need to capture once we are there?" - and that is where the technology decision matters.

LiDAR vs photogrammetry - the one question that decides it

Both LiDAR and photogrammetry produce a point cloud - a precise three-dimensional dataset of the surveyed area. The difference is in how they get there and what they can see through.

LiDAR fires laser pulses at the ground and measures their return. Because the pulses can pass through gaps in a tree canopy and return from the ground beneath, LiDAR can map what is underneath vegetation - something a camera simply cannot do. Photogrammetry works by stitching together a large number of overlapping photographs with high precision, producing a point cloud alongside other deliverables such as orthophotos and 3D models. It is highly accurate and produces rich visual outputs, but it needs clear line of sight to the ground.

Bob's approach when a new enquiry comes in is straightforward. "The first question I'm usually asking is what is on the land and what are they trying to get out of it?" The answer almost always points clearly to one technology or the other. "If they tell me there's lots of trees, forestry, vegetation, LiDAR. If they tell me it's mostly open light grass and there's lots of hardscape, things like that, then it's photogrammetry."

When to choose LiDAR

If the site is heavily vegetated - forestry, scrubland, overgrown fields - and the client needs to understand what is beneath the vegetation, there is no alternative. "LiDAR is the only technology for that," Bob says plainly. It is also the right choice where ground-level features such as drainage channels, archaeological remains or terrain detail are hidden under a tree canopy. The laser penetrates; the camera does not.

When to choose photogrammetry

For hardscape sites - cities, industrial facilities, construction sites, roads and built-up areas - photogrammetry is generally the stronger option. It is faster to process, produces visually rich outputs that are easy for stakeholders to interpret, and delivers the accuracy required for engineering and planning purposes. Light grass, open fields and sites without a significant vegetation problem are also well suited to photogrammetry.

The practical upshot is that most clients, once they understand this distinction, find the technology decision straightforward. The answer usually becomes clear the moment you describe the site.

Full transcript

Show transcript

Interviewer:

[00:00:02] This will be from a client's point of view. How do you approach when they kind of get on to you with their spec? How do you approach then selecting the right drone or survey method and especially when factors like terrain, accuracy and access come into play?

Bob Foley: Engineers With Drones

[00:00:16] Yeah, absolutely. So let's start at the end. The drone doesn't care about access except for things like airports and whatnot. The drone doesn't see the ground underneath it. doesn't really care about it. So long as you have a takeoff and landing point and you can access a sufficient amount of points to put down some ground control, then the drone will go wherever it likes, wherever it's legally allowed to go. So that's not a factor.

An interesting thing to consider is, you never want to be thinking about the drone. You always want to be thinking about the technology to use. So there are two broad technologies in land surveying, LiDAR and photogrammetry.

Okay, LiDAR, a bunch of laser beams shoot out, take measurements, and it generates what's called a point cloud. Photogrammetry, you take a load of photographs, you technically stitch them all together in a very precise way. and you generate also a point cloud with other deliverables from that as well.

Depending on what you're trying to achieve, it's very important to choose the correct technology.

LiDAR, when my clients ask, the first thing I ask is what sort of land you want to map. If they say it's highly vegetated and I really want to know what's underneath, then LiDAR is the only technology for that.

If you have a lot of hardscape land, like in the middle of a city or a built up area where it's lots of roads, footpaths, houses and so on and so forth, small gardens, light grass, that sort of thing, then photogrammetry is a much better solution for that. So the first question I'm usually asking is what is on the land and what are they trying to get out of it?

If they tell me there's lots of trees, forestries, trees, forestry, vegetation, LiDAR, if they tell me it's mostly open light grass and there's lots of hardscape, things like that, then it's photogrammetry.

Drone survey FAQs

How do you choose the right type of drone survey?

You never really want to be thinking about the drone, you want to be thinking about the technology. The two main technologies for are LiDAR and photogrammetry. Both LiDAR and photogrammetry generate a point cloud, however LiDAR has the ability to survey land through trees and vegetation. Photogrammetry however is the better solution for hardscape land, including cities and built up areas.