0

Tag: lidar

Australian start-up develops drones that fly underground

By GCR Staff

Australian company Emesent has developed software that allows autonomous drones to create mapping of underground spaces such as mines and tunnels.

The company was founded by researchers at the robotics department of the Commonwealth Scientific and Industrial Research Organisation, an Australian federal research agency. While there, they began created “Hovermap”, a technology that allows drones to explore confined spaces such as mines, transport and utility tunnels.

The drones, which do not require a human controller, rely on the LiDAR laser systems used by self-driving vehicles, as well as collision-avoidance sensors and GPS chips. They can also perform other tasks, such as taking gas readings

A video of the system in action can be seen here.

Read More: GCR

Surveying with Drones: The Key Differences Between Aerial LiDAR and Photogrammetry

The following is a guest post from Dustin Price, licensed land surveyor and operations manager at Landpoint: a surveying, aerial data and technical services provider.

There has been an influx of new and, in some cases, game-changing surveying technologies that have popped up over the past few years. Arguably the biggest of these technologies is unmanned aerial vehicles (UAVs), which has allowed surveyors to collect data in a fraction of the time it would take using traditional methods.

The rise of UAV surveying has also created a choice for those that need aerial data: LiDAR or photogrammetry. Here are a few key ways in which these two technologies are different.

Read More: Drone Life

Monitoring Coastal Erosion with UAV Lidar – Comprehensive Surveying of Coastal Topography

By Michel Assenbaum

The French Mediterranean coast is a complex natural environment where geology, climate and the sea interact and continuously reshape the landscape. Coastal erosion and the availability of drinking water are two major coastal management issues that necessitate precise monitoring of the morphological changes to the shoreline.

UAV Lidar is being used in this region to produce comprehensive topographic surveys with unprecedented productivity and level of detail, and several Lidar surveys are planned over the next two years.

Read on for details of the context, technical setup and results of the very first survey which took place in January 2018.

More: GIM International

LiDAR for Drones: Direct Georeferencing vs Traditional Aerial Triangulation Systems

Earlier last year, Pierre Chaponnière, Application Engineer at YellowScan, talked about the benefits of Direct Georeferencing for simultaneous LiDAR / Photogrammetry versus Traditional Aerial Triangulation systems and exemplified its use with a case study of a quarry in France. This subject picks up on some of the information we discussed in an article around how to use a drone for aerial surveying instead of arguing about Photogrammetry vs LiDAR.

To start off the presentation, Pierre discussed a bit about the main differences between Aerial Triangulation and Direct Georeferencing. As Pierre puts it, “Aerial Triangulation (AT) is sort of an upward workflow”. Simply put, this process works through the identification of ground control points (GCP) or tie points on the collected images – this could be images or LiDAR point cloud – to position and orientate your platform, and then generate results, such as an orthophoto.

On the other hand, Direct Georeferencing (DG) consists in using high-grade IMUs – YellowScan mentioned the Applanix APX 15 – resulting in “a centidegree accuracy in rolling, pitching, and heading”. This means it’s possible to get the full accuracy of both the platform’s position and orientation, and accurately position each point of your LiDAR or photogrammetry pixel. “This gives you the ability to quickly georeference any points because you already georeferenced and you can just position your data”.

Putting it into practice

After introducing and comparing both methods, Pierre moved onto the case study of a 25 hectares (ha) quarry site, with a 140m deep pit and high steep walls, to the south of France. The case study consisted of collecting different data, such as quarterly maps, and volumetric calculations, by using three different survey methods on the same day, with the same weather conditions and hour slots. One of the methods was a Terrestrial LiDAR System (TLS) – a Trimble TX5 mounted on a tripod, which reaches a frequency of up to 976kHz, and has a range of up to 120m.

Then, there was the DJI Inspire, used as a photogrammetric sensor for the Traditional Aerial Triangulation system, equipped with a 16MP camera.

At the same time, YellowScan used its LiDAR scanner Surveyor equipped with the Applanix APX15 on a drone, mounted in a combo with a 24MP camera.

The set up

Setting up a TLS isn’t an easy task. Initially, the network set up is rather tricky, as you need to set up a checkerboard in order to actually position your tripod and achieve an absolute positioning reference to the scanner. Then, you need to move around with a few reflective spheres to relay your station from one to the other. “So, there’s a lot of movement and a lot of moving parts around in Terrestrial LiDAR scanning”, Pierre adds.

“Then, in terms of the DJI Inspire and the photogrammetry process, the operative constraints are fairly simple in terms of flight planning,” Pierre continued, “The only thing you need to do pre-flight, is just having a network of ground control points and targets in order to actually shoot them from the drone, and then being able to visualize them on your acquisition. So, this takes a bit of time and effort to deploy”.

In regards to the YellowScan Surveyor Combo, you only need a GNSS base station that works in PPK mode. This means you can be five kilometers away from it with the drone, and you’ll still get good correction results. However, since the scanner has a limited range, you need to adapt your flying altitude to the terrain.

Timing and results

After calculating and placing each method’s results side by side, it becomes apparent where the real differences, advantages, and disadvantages are over each other.

In 6 hours, the TLS covered 22 stations, 1 hectare, and generated 2Gb of data, whereas the AT process with the DJI Inspire covered 25ha, took the same amount of time (with 10x10min flights and preparation), and generated 6Gb of data. However, due to the luminosity variations, the DJI Inspire needed two days to complete the process (3 hours each day in a specific time slot).

On top of that, the YellowScan Surveyor Combo, equipped with the DG system, managed to cover 25ha in 2 hours, with only 4x10min flights and preparation, as it only needed one passage over a specific part of the quarry to capture the necessary points. The result was 4.1Gb of data from the LiDAR scanner, and 6.7Gb from the 24MP camera.

Additionally, you need to take into account the amount of time of manual processing (where you need to intervene in the process to achieve the desired result), and machine processing (where you leave the computer to deal with the data alone).

So, the TLS took +3 hours to finish the process: +2 hours of moving spheres around and aligning checkerboards, and +1 hour in exporting the data to the computer.

The DJI Inspire didn’t take any time in the manual processing phase, since it is an automated process. However, it took +12 hours for the computer to process the Aerial Triangulation, detect GCPs and create a dense cloud. Furthermore, YellowScan also decided to perform the AT process for the 6.7Gb data captured from the high resolution 24MP camera, which ended up taking +40 hours.

Finally, the YellowScan Surveyor took +3.5h to perform the PPK process, classify and match lines, and process DG images as well as ortho generation. Additionally, the computer took +2h to perform the matching and classification process.

Coverage production rate

In the end, all of these steps translate to a single product from each process:

The TLS generates an unclassified 2Gb LAS file, with a Ground Sample Distance (GSD) of 1cm, meaning it has a production rate of 0.1ha/h;

The DJI Inspire 16MP camera AT process resulted in an unclassified 0.6Gb LAS file, with a GSD of 10cm, ending in a higher production rate of 1.4ha/h, while the YellowScan 24MP camera AT process finished with an unclassified 10Gb LAS file, with a GSD of 2cm, and a lower production rate of 0.5ha/h.

The dominant one here was the YellowScan Surveyor, which generated a classified 2.7Gb LAS file, with colorized DG, and a GSD of 5cm. The production rate was the highest one of the four, at 3.3ha/h.

Point-by-point vs Cloud-to-Cloud vs Section-to-Section accuracy assessment

To validate the acquired products and their accuracy when compared with the real world, YellowScan used the RMSE measure, as shown in the image above. On a point-by-point measurement (left-side image), the YellowScan Surveyor didn’t stand out when compared with the photogrammetric solutions.

However, when you move on to a wider area (image on the right), you start to see the differences between them. The image represents a parcel of ground with steep curves and slope changes. While the YellowScan Surveyor with the Direct Georeferencing system doesn’t show any errors, the DJI Inspire produces a lot of artifacts when generating the model when it comes to “brutal slope changes”.

Pierre said: “The Aerial Triangulation process works well, but not really at slope changes, [as it] generates a lot of artifacts there”.

Moreover, Pierre also talked about vegetation penetration, as well as infrastructure mapping, and showed a comparison between the two – check images below.

On the left side, although the YellowScan Surveyor leaves a few holes in denser vegetation areas, it does show a better representation of what it looks like than the DJI AT process. Then, on the right, you can see how much more detailed the infrastructure is on the YellowScan Surveyor example.

The conclusion

To wrap up the presentation, Pierre talked about the benefits of using a combo like the YellowScan Surveyor, with a 24 MP camera and the Direct Georeferencing system – in this case, the Applanix APX 15 – over an AT Photogrammetry solution.

To start with, the LiDAR/photo DG solution provides faster survey and processing times. Ground truth points or GCPs are not as critically needed as they would be in a AT photogrammetry process. The only point that needs to be well positioned is the landmark the base station is setup on, the rest would work rather as validation points for reporting and quality checks.

A single flight path of a LiDAR survey offers much wider coverage than photogrammetry, It isn’t affected by sunlight as opposed to AT photogrammetry which is light dependent; image correlation issues don’t impact the result; and it has the ability to capture fine infrastructures or objects, such as power lines, and conveyors.

Additionally and on a more general note, remote sensing surveys provide safer operations, no disturbance or operation downtime, as well as faster data collection and a wider field of view.

One of the questions we posed in last year’s article was around whether or not photogrammetry was better than LiDAR, or vice-versa. The answer is that it all depends on what you want to do. However, YellowScan created a solution that combines both technologies, and by adding a Direct Georeferencing board to the mix, it ends up offering better results.

As YellowScan mentions in one of the slides of the presentation, the YellowScan Surveyor combo is “the one tool every surveyor needs”, and by combining the best of what photogrammetry and LiDAR have to offer, it’s hard to argue with that assessment.

 

About the Author

Technology in general makes João Antunes tick, but the specific ways it has created and changed the landscape in IT, gaming and computers ignited curiosity that’s turned into a passion for him. As the son of a journalist writing about how these industries have emerged and evolved, he has an incredible perspective when it comes to understanding the kind of disruption new technologies can create in a given space. He’s committed to showcasing what that disruption will mean for professionals as they work to utilize brand new pieces of hardware, software, systems and processes.

 

Should you Choose LiDAR or Photogrammetry for Aerial Drone Surveys?

The question of photogrammetry or LIDAR is one survey professionals have explored in great detail over the past few years. Many drone pilots face this question, and wonder which one of the solutions will work best for them. What’s the real answer to the question? As someone with a background in land surveying and photogrammetry, PwC Polska’s drone team manager Aleksander Buczkowski thinks the differences between each solution are obvious, but not so straightforward for someone without proper knowledge.Growing up surrounded by thousands of maps from his father – a University professor of cartography -, Aleksander ended up following his steps. He obtained his Master’s degree in GIS and Geospatial Technologies, and soon moved into business, where he spent a few years working on various projects related to HD maps for autonomous cars. However, two years ago, he developed an interest “in the possibilities of low altitude photogrammetry and remote sensing”, as he “realized combining the science that has been previously reserved to airplanes and satellites with drone platforms has a potential to disrupt the way we think about geospatial data.”“When you start to get deeper, the level of detail and ease of use of this data, can transform the way businesses operate”, Aleksander continued. “Mining companies can generate detailed 3D models of their sites on a daily basis, energy companies create digital twins of their entire infrastructure, construction companies monitor progress on each square centimeter of their capital project. But it’s not easy to manage such a change and make it work on a large scale. This is why I’ve joined PwC, that opened Global Center of Excellence in drone technologies in Warsaw, Poland.”

Image courtesy of Multivista Systems

As Manager of PwC Polska’s drone team, Aleksander helps companies around the world to successfully integrate drone into their workflow, which include different jobs such as: advisory projects on drone sales strategy; 3D models’ generation of mines in the middle of a jungle; and developing deep learning solutions to automate drone-based asset management.

To avoid the propagation of myths and misconceptions around UAV LiDAR and photogrammetry, as well as to answer many of the clients who ask him which solution is better, Aleksander decided to write the “Drone LiDAR or Photogrammetry? Everything you need to know” article. In the article, he talks through the various factors (Data Output, Accuracy, Data Acquisition, Processing, Efficiency and Cost) that are taken into consideration and help differentiate, as well as understand how each technology works. As Aleksander says in his article: “these two technologies have as many differences as similarities”.

LiDAR advantages mean you can generate more precise 3D cloud files; it doesn’t depend on light conditions; achieves high relative accuracy (1-3cm) out of the box (with the help of an IMU (inertial motion unit) and GNSS receiver); and data acquisition and processing operations are much faster. However, LiDAR-generated files are non-RGB, meaning it can be challenging to interpret.

On the other hand, Photogrammetry generates full-color 3D and 2D models such as raw images, orthomaps, Digital Surface Models and 3D points clouds.

“Beautiful 3D point clouds and 3D mesh models, which are the output of photogrammetric processing, look so realistic that people don’t realize the limitations of the technology”, Aleksander said. “The photogrammetry software is not yet able to reliably generate models of narrow objects on a large scale such as powerlines, it cannot penetrate a tree’s canopy, requires specific weather conditions, a large number of ground control points and a long time to process the data. Each project and each case should be analyzed separately in order to select the optimal technology.”

In terms of cost, different factors come into account: the software & hardware, time of preparation, and the drone itself. Aleksander provides an estimate of $50,000 – $350,000 for a LiDAR solution, while for Photogrammetry the prices go down to $2,000 – $20,000. You might think it is clear what the better technology is once you look at these numbers, but time is money, and LiDAR might save you in that aspect depending on the use case business model.

“Photogrammetry data can weight over 30 times more than LiDAR”, Aleksander continued. “A regular photogrammetry inspection that I work with easily exceeds 50GB (compared to 2GB LiDAR file). It’s a lot of data and you must be able to use, analyze and measure. On the other hand, LiDAR results aren’t always easy to interpret and non-engineers tend to be not capable of using it. At the end, one of the most important challenges you will face is how to make sure that your client will be able to use the data effectively and efficiently. Without solving this challenge you won’t succeed in the drone business.”

That’s what it is about: which technology fits your or your client needs, not which one is “better”. Ultimatrly, this conclusion isn’t a decisive one, but one solution that might provide the kind of definitive answer professionals are looking for. Aleksander believes in “the future is the sensor fusion. Complementary LiDAR and camera sensors will be a single solution to rule them all”. Interestingly enough, in December 2017, we covered YellowScan’s presentation about the benefits of Direct Georeferencing for simultaneous LiDAR / Photogrammetry versus Traditional Aerial Triangulation, where they showed the results between Photogrammetry vs LiDAR vs simultaneous LiDAR / Photogrammetry solutions, and more solutions will be available soon.

Is this the future we’re looking at when talking about aerial surveys? As more and more people think of drones as tools to accomplish a variety of tasks, we’ll certainly see a dedicated focus on the expanded capabilities of these tools, and that includes being able to collect data of all types and sizes.

 

About the Author

Technology in general makes João Antunes tick, but the specific ways it has created and changed the landscape in IT, gaming and computers ignited curiosity that’s turned into a passion for him. As the son of a journalist writing about how these industries have emerged and evolved, he has an incredible perspective when it comes to understanding the kind of disruption new technologies can create in a given space. He’s committed to showcasing what that disruption will mean for professionals as they work to utilize brand new pieces of hardware, software, systems and processes.