What do Drones, LiDAR Mean for Aerial Surveying, Mapping?
Now is a special time for geospatial service providers. Many call it as important a time in the history of geospatial technology as the introduction of geographic information systems (GIS). Arguably, unmanned aerial systems (UAS) and 3D data acquisition tools are undergoing some of the most notable innovations, impacting aerial surveyors and mappers most.
The Association for Unmanned Vehicle Systems International (AUVSI) projects that drones will have an economic impact of $82 billion by the year 2025. According to the most recent POB Laser Scanning Surveying Trends study, 19 percent of respondents reported using UAS in 2015, compared to 38 percent in 2016. Over the same time period, the use of photogrammetric cameras slightly decreased by 9 percentage points, and the use of laser scanning/imaging tools increased by 5 percentage points. While aerial LiDAR use dropped from 33 percent to 18 percent, 69 percent of respondents to the 2016 study report that demand for laser scanning has increased.
So, what should aerial surveyors and mappers do with all of this information? Will drones replace manned aircraft systems? Will LiDAR replace photogrammetry? POB decided to explore the state of aerial applications through the insight of stakeholders. They covered the planning that goes into aerial surveying and mapping today, and shared how they decide when to use what tools.
“Drones are a huge factor,” says Mike Tully, CP, GISP, president and CEO of Aerial Services Inc. in Cedar Falls, Iowa.
The company, celebrating 50 years of remote sensing and mapping services, started working with drones three or four years ago. Tully says drones are, for the first time in history, enabling anyone to put sensors in the national airspace by drastically lowering the barriers to entry.
When he joined the business 20 years ago, aerial surveying and mapping service providers needed a lot of capital to buy manned aircraft, expensive large-format cameras and computing technology to process the data. Today, for $5,000, nearly anyone can put a very capable camera in the air, collect high-resolution 3D data and make maps with software that is very automated, Tully says.
He expects that drones will enable a whole host of new mapping services that haven’t yet been possible with manned aircraft because of safety issues and higher costs. In projects that benefit from multiple flyovers, for example, drones may be much easier and cheaper to use than planes and helicopters.
“Drones will begin competing with traditional manned aircraft projects, especially as the federal regulations allow beyond-visual-line-of-sight. Today they don’t, for the most part. Tomorrow they will,” Tully says.
“I feel like I have seen an exaggerated example of the technological changes that the rest of the industry has experienced,” says David Day, CP, executive vice president of Philadelphia-based Keystone Aerial Surveys Inc.
Aerial surveying was a mature and stable industry when he joined the aerial data acquisition services company in the mid-1990s. At that point in time, he says film cameras were regularly used, and creating deliverables required a lot of time and manpower. Soon after, he remembers GPS technology emerged, followed by computer based “soft copy” photogrammetry from scanned film; then came direct digital data acquisition.
Software and computer capability advancements in the early 2000s made it possible for the company to complete state-wide, high-resolution data collections in a few weeks and deliver products in just months. Now, with computer algorithms such as semi-global matching and structure from motion, small consumer cameras are able to be used from both manned aircraft and UAS.
Philippe Simard, Ph.D., president of SimActive Inc., says he too remembers when scanned film was the norm, back when the company started the development of its Correlator3D photogrammetry software. He says drones have introduced a whole new dimension to the industry, which he calls the “democratization of photogrammetry.” Once reserved for people who had years of experience, Simard points out that the price of drones coupled with the ease of use of products like Correlator3D is making the technology available to anyone. “We thus see an exponential growth in mapping applications from drones and use of our software.”
In a nutshell, Day sums up the technological evolution of photogrammetry as photographic and physical to IT-based. On the one hand, he says it is good because it fosters new energy and ideas. On the other hand, he says it is bad. “Automation and reliance on software can create users who are unaware of the principles behind photogrammetry that play a role when software fails.”
Plane, Helicopter or Drone?
When it comes to choosing which aircraft to use for aerial data acquisition, Day says helicopters are often selected for low, slow-flying projects including mapping, patrol and inspection. While the platform used to be used for film projects, he says it is now usually used for dense LiDAR collection.
Deciding whether to use an airplane or a drone can be a very difficult choice. For large-area collection, an airplane is the best option; for one, FAA regulations restrict drone flights over people. Manned flights have no such restrictions. However, Day says that even if such flights were permitted by the FAA, an airplane would still be the better choice because it is less costly. For small, local projects or for work that a manned aircraft cannot perform, drones make the most sense. However, Day says even small projects can be best served with an airplane if the travel distance for the pilot is significant.
As for survey-grade data, Day — who defines this as products meeting the ASPRS horizontal and vertical accuracy specifications by using pixel size of imagery — says it can easily be achieved by imaging and LiDAR systems mounted to manned aircraft systems. “But from Keystone’s published studies, we have determined that survey-grade data can be generated by a UAS in very limited and controlled situations that are not really cost effective,” he says. “In general, we believe UAS data is best suited for products where accuracy needs to achieve three to four times the pixel size.”
In the end, a photogrammetry project is the same for any type of aircraft or sensor, Day says. The area must be covered with a user-specified amount of overlap between strips. “Even navigating the airspace is similar for manned and unmanned,” he points out.
When planning a flight, Tully says it is important to understand the flight and positional accuracy specifications. Flight planners must mach accuracy specifications with altitude, speed and what type of aircraft is needed to cost-effectively meet the project goals. Airspace flight restrictions are an additional factor that influences flight plannnig. Pilots are not permitted to fly over many areas of the country, including airports. Companies in the business of aerial surveying and mapping should know how to identify possible flight restrictions and either obtain waivers or adjust flight plans to avoid certain airspace. Weather is also a major factor in flight planning. “Weather remains inherently unpredictable, so we’ve got to plan around weather. Logistically, this is often a complicated process involving a lot of moving parts,” Tully says. “When the weather clears, we need to have equipment at the project site so we can do the required data acquisition before that flight window closes.”
Photogrammetry or LiDAR?
Similar to aircraft, clients either directly dictate which sensor systems will be used, or their needs — type of imagery and level of accuracy — guide the choices made by the user and service provider.
Tully says most remote sensing and mapping requires imagery and some kind of point cloud. Photogrammetric techniques can be used to derive a point cloud from the photography, or the point cloud can be collected directly using a LiDAR sensor. LiDAR is typically more expensive than a camera for a given application.
Aside from cost, a key difference between photogrammetrically-derived point clouds and LiDAR is the ground. Tully explains that, because LiDAR uses active sensor technology, it can push through vegetation and reflect off the ground beneath. “Photogrammetrically derived point clouds are simply going to show the surface of things,” Tully says. “So LiDAR gives us a distinct advantage by giving us both the surface of things, which is very important, but also the bare earth elevations that photogrammetry alone just can’t give us. … LiDAR will generally give us a leg up and give us much more accurate models of the earth’s surface, which is, frequently, what’s needed.”
Since photogrammetry is significantly cheaper than LiDAR in many cases, especially when both photography and elevations are needed, it remains useful and important in many applications. “That’s why we’re seeing drones and even manned aircraft often fly borrow pits and coal piles to calculate volume and things like that using only aerial photography — and photogrammetrically-derived elevations. Because there is little or no vegetation obscuring the ground, the 3D point clouds derived from the photography are accurate enough for those purposes.”
Since LiDAR covers the ground and the surface of things, and photogrammetry only gets to the surface, as LiDAR sensors become less costly, Tully says he can see LiDAR dominating 3D modeling of the earth’s surface. “I can see a day when building 3D models of things under the sensor can’t be produced as efficiently using photos only because our LiDAR sensors will be powerful enough and cheap enough to make the photos-only method of remote sensing unnecessary.”
What Surveyors Should Know
For surveyors who, perhaps, are considering expanding their business to include aerial services, Tully says it is no simple step and should be considered carefully. A large part of what companies like Aerial Services do is actual mapping. “Don’t underestimate the complexity and difficulty of making a map. It’s not the same as surveying and its not simply ‘aerial photography,’” he says.
Remote sensing and mapping require a good technical understanding of photogrammetry; this includes knowing how to stitch remotely-sensed data together to make a uniform dataset that can be objectively tested for accuracy. Surveyors should also understand the limitations of processing software that depends upon the science of photogrammetry, which today automates a lot of the unmanned processing phase. “There are assumptions and compromises that software is making to produce these datasets very easily and very quickly,” Tully explains. “If the practicioner does not understand them, they might misrepresent the quality or accuracy of the product that comes out the other end.”
Many of Day’s clients see the introduction of drones as a way to bring total surveying or mapping projects under one roof. Unfortunately, he says many companies have tried this with manned aircraft before and have failed. He expects the success rate with drones to be higher, but highlights that to be safe, legal, deliver exceptional data and be cost effective requires a dedicated group of people. “Any surveyor who wants to perform aerial work with drones should know that they do not necessarily make data collection cheaper. Although the cost of entry is cheaper, other factors like labor and incidentals can be higher. Also, you will crash them and there is a steep learning curve to the software to generate products.”
To those surveyors considering manned operations, Day says aircraft break, digital cameras are expensive and post-production software is not cheap. In order to support these costs and make business sense, aerial surveying should be performed in large quantities.
On the other hand, Simard acknowledges that drones have been perceived as a threat by many surveying and mapping businesses; the rationale being that their low price could allow anyone to start collecting data and become competition. Echoing Tully’s point though, Simard says, “The truth is that the process is not that simple, at least not if results are to meet certain quality standards. The main challenge for anyone new to aerial surveying is to learn and understand the whole photogrammetric process to achieve desired project requirements.”
In the grand scheme of things, every technology represents just another tool — including drones and LiDAR sensors. What surveyors and mappers really need is to make sure the people using those tools are capable and competent and licensed, Tully says. “The problem is not with the technology. The potential risk is the exploitation of that technology by unqualified people.”
Day agrees that the key challenge is ensuring that quality does not suffer in the pursuit of reduced prices and increased automation. “Both land survey and aerial survey — or photogrammetry — has a long tradition of quality,” he says. “In a data-driven culture where timeliness is crucial, aerial surveying will still be relevant and useful, if we are willing to adapt.”