After the cathedral of Christchurch, New Zealand, was hit by an earthquake, drones and advanced photogrammetry software supported the rebuilding work.
Surveying a damaged building can be dangerous. Mapping, using drones, reduces risk to staff and costs to the community. This case study of the iconic cathedral of Christchurch, severely hit by an earthquake, demonstrates how drones and advanced photogrammetry software delivered the orthomosaic map, enabling the accurate spatial planning needed to rebuild the cathedral.
In February 2011, New Zealand’s second most populous city was rocked by an earthquake. The iconic Christchurch Cathedral was shattered in the shake, and the clean-up is still ongoing. Christchurch's central city and eastern suburbs were badly affected.
Before the cathedral could be rebuilt and the 'red zone' surrounding it rejuvenated, a full survey was required. Christchurch City Council’s surveyor Jed Clement, licensed cadastral surveyor, stepped up to the task with the help of drones and Pix4Dmapper.
Locals describe Cathedral Square as "the heart of the city" and as being "key to Christchurch". It sits in the centre of Christchurch, both metaphorically and literally. The garden city, with its large urban parks bisected by the sleepy Ōtākaro Avon river, is known for agriculture, for being the gateway to Antarctica and, more recently, for earthquakes.
New Zealand is stretched across a fault line and earthquakes are common, although seldom as severe as the 2011 quake. By August 2012, the area had experienced more than 11,000 aftershocks of magnitude two or higher. Aftershocks were felt up to 300 kilometres away from the epicentre.
Strict building standards no doubt saved many lives. Scientists estimate that the shake that damaged the cathedral would have “totally flattened” most cities around the globe. The timber-framed homes favoured in New Zealand are relatively resistant to earthquakes, and most damage was sustained in poorly-designed buildings, or stone structures like the Christchurch Cathedral.
Prior to the 2011 earthquake, the cathedral had been damaged by earthquakes in 1881, 1888, 1901, 1922 and 2010. However, the greatest damage occurred in 2011. The first shake destroyed the spire and part of the tower, and left the rest of the building severely damaged. Aftershocks collapsed the west wall of the cathedral, and what was left of the tower had to be demolished in 2012.
Rebuilding After the Earthquake
As the city and the nation debated whether the Cathedral should be rebuilt at all, worshippers gathered in a temporary ‘Cardboard Cathedral’ made out of comfortingly earthquake-resistant materials – including cardboard. But now the cathedral is being rebuilt and commercial development in Cathedral Square and the surrounding area encouraged. Access to the area has been limited due to quake damage, and it’s hoped the development will revitalize the area.
To assist with the rebuild, the Christchurch City Council team launched a drone flight to capture ground levels and provide an up-to-date orthomosaic drone map of Cathedral Square to allow for accurate spatial planning.
The Benefits of Drones in Dangerous Situations
Much of Cathedral Square is open, but there were areas of the Square that were impossible to access due to the risks relating to construction as well as the damaged buildings, including the cathedral. Aerial photogrammetry was therefore the best choice for capturing data in these areas.
The drone could fly inside the restricted perimeter fences without risk to the operator. Just as importantly, Pix4D’s algorithms allowed for the optimal capture of imagery to render a high-quality 3D model that the surveyors could use to take precise measurements – all without entering the site.
Mapping an Inaccessible Area with Drones
The flight team met in Cathedral Square at 8am on a Sunday morning. The early start meant fewer people around the square and fewer vehicles on the road. While this caused less disruption to the public, it also had advantages for the team. Moving objects (like cars and people) may appear in the orthomosaic as transparent artefacts. While it is possible to remove these 'ghosts' and improve the appearance of the orthomosaic, the early start allowed the team to avoid capturing them in the first place.
The Christchurch City Council survey team’s drone pilots licence is pending, and they currently operate under New Zealand’s CAA Part 101 operating rules, which also regulate balloons and kites. The aerial mapping flight was approved by the city’s Roading Authority and the cathedral trust.
The team hoped for overcast weather, and got it. “We were concerned about the surface being quite reflective, which would mean losing detail in the final outputs,” says Clement. “But the morning of the flight could not have been better, being overcast and with no wind.” A total of four flights were completed: two oblique and two grid nadir to capture as much information as possible.
“Unfortunately, we had an issue with the connection to the drone on one of the flights,” says Clement. “That meant we were missing one set of oblique images over most of the square, which resulted in missed detail on the cathedral and surrounding buildings.”
Despite this issue, the team was able to reconstruct the 3D drone model in less than 23 hours in Pix4Dmapper aerial photogrammetry software.
Before take-off, eight ground control points (GCPs) were levelled to a 5mm accuracy. A further 12 checkpoints were added during processing, giving the mapping project an average ground sampling distance (GSD) of 1.38cm. “Quality ground surfaces and reporting – plus ease of use – is why we chose Pix4D,” added Clement.
Modelling a Moment in History
The model gave the team the certainty they needed to begin the detailed design phase of the southern portion of the Cathedral Square rebuild. This part of the rebuild is to coincide with the commercial development that is underway on the southern perimeter of the square, and is due to begin opening in late 2019.
Regenerate Christchurch notes that: “Redevelopment will acknowledge the past and the events that have shaped the city, while reflecting the best of the new… This is an opportunity to breathe life back into Cathedral Square and re-establish it as the heart of the city.”
The model of the square and broken cathedral is not only a useful tool, but the aerial photography is a snapshot of a moment in the city’s history.
The original version of this article was published on Pix4D.com. Last updated: 24/06/2020
From New York to Dubai to Myanmar, more smart cities are springing up across the globe. As more countries start to digitally transform, the futuristic cities and state-of-the-art gadgets that once belonged only to the realms of science fiction may soon become our reality... and they will be made possible with the advancement of the geospatial industry.
The global geospatial analytics market is estimated to be worth USD$134.48 billion by 2025, with the market registering a compound annual growth rate of 15% between 2019 and 2025[1]. Asia Pacific is also expected to see the highest growth during that period, fuelled by numerous smart city initiatives such as ASEAN Smart Cities.
These indicators point to the increase in demand for geospatial services, which will no doubt also bring improvements in quality to geospatial services and technologies. Led by factors such as increasing digitalization, access, ubiquity in unmanned aerial vehicle (UAV) usage and the opportunities of the Belt and Road Initiative (BRI), the geospatial industry is expected to remain a key player across the world in 2020.
Increasing Digitalization
Ever since the world entered a technological boom, we have been on a steady climb to become a digital world. Geospatial technologies will continue to enable us to build smart cities with the integration of digital technologies into work processes becoming a commonplace practice.
For example, the implementation of Integrated Digital Delivery (IDD) is one of the key elements in the Singapore government’s Construction Industry Transformation Map. IDD integrates every team member and stakeholder into the workflow, increasing connectivity between each member to improve efficiency and effectiveness. Cloud-based visualization and collaboration platforms like the HxDR from Hexagon allow data to be sent to the cloud as they are recorded. 3D point clouds and Building Information Modelling (BIM) can also be easily incorporated into the IDD workflow. This way, all parties involved in a project have access to real-time data and are updated on any new or changed information.
This approach highlights how the digitalization of geospatial technologies supports the construction industry and is important in ensuring that urban planning and construction workflows are operated efficiently, and in tandem.
Access for More Users
While the geospatial industry has always had a strong footprint in the construction industry, it can expand its horizons far beyond its roots. Lidar technology is used in laser scanners and trackers to provide accurate 3D models and land-over classifications to map areas as large as cities. However, there is a lot of anticipation about how geospatial technologies can be incorporated into other businesses. For instance, the automobile industry is looking into how Lidar can be used as 'eyes' for autonomous vehicles. Authorities can similarly use Lidar for urban planning and disaster response.
Furthermore, geospatial services are increasingly moving online as Software-as-a-Service (SaaS), allowing users to access a software’s functions over the internet. Geospatial services such as SaaS essentially mean that these services will become accessible to even beginning users. Geospatial providers are likely to improve the intuitiveness and user-friendliness of their products to make them more accessible for prospective users.
UAVs
The global UAVs market is forecasted to grow to US$40.6 billion by 2028 from US$17.0 billion in 2018[2], and will play an increasingly important role in optimizing processes in various industries.
Major construction companies in other countries have begun to integrate UAVs into their work processes. The engineering community is one of the first industries to adopt UAV technology to aid virtual design and construction. Not only do UAVs improve the safety of work sites and are cost-saving compared to traditional surveying methods, but their aerial perspective also offers near-limitless ways to gather and analyse data. UAVs in geospatial technology have been used to scope out massive areas, such as a whole city, within a few hours. The integration of 3D visualization tools in UAVs will further revolutionize the way that geospatial technology can inspect, survey and map.
Opportunities on the BRI
Since 2015, China’s proposed SG$900 billion BRI project has encompassed opportunities amounting to SG$155 billion in the transport and building sectors. With over 200 projects spanning various continents[3], the precision and speed that geospatial services can provide are invaluable to such projects, and the ability to visualize the outcomes of projects is a great advantage for every party involved.
A notable BRI project is the Edirne to Kars High-Speed Rail Line in Turkey. The 2,000km line is the key link connecting the Guangdong and Shenzhen ports to Rotterdam, while also connecting the Asian markets of Myanmar, Bangladesh, India, Pakistan and Iran. A project of this scale will require rigorous and thorough planning to ensure that all these locations are linked, which may also present geographical problems. By using geospatial technology to map and survey locations, any construction challenges faced can be solved and even avoided well in advance.
Furthermore, critics have raised concerns regarding the BRI, such as the safety of sea channels and environmental concerns, as 90% of global commercial trade and 60% of the world’s total oil volume is still conducted through shipping[4]. It is important that these channels remain safe for use. With technology like Lidar, accurate maps can be plotted to ensure new trade routes will not obstruct existing ones. Lidar can also be used to ensure that no excessive damage is caused to the environment during construction.
Conclusion
As the various factors look set for continuous growth, opportunities for the geospatial industry are abound in many areas. In particular, smart cities – a market that will be worth US$833 billion by 2030[5] – is in the driving seat to be the main growth engine for the industry as cities develop future infrastructure with geospatial technologies.
Please note that this article was written before the coronavirus outbreak.
Author: Mark Concannon
02/06/2020
The use of a UAS to acquire geodata for mapping purposes has evolved beyond infancy and is now rapidly maturing. How will it evolve in the foreseeable future?
The use of an unmanned aerial system (UAS) – cameras and Lidar sensors mounted on an unmanned aerial vehicle (UAV or ‘drone’) – to acquire geodata for mapping purposes has evolved beyond infancy and is now rapidly maturing. How will UAS mapping evolve in the foreseeable future? To envisage where exactly UAS technology is heading, it is appropriate to start with the big picture before examining the details.
So what is the current big picture for unmanned aerial systems? How are they embedded in today’s society? First of all, our planet is confronted with climate change. The most threatening effects are sea-level rise and lengthy heavy rainfall putting valleys, rivers, lowlands and deltas at increased risk of flooding. Each year, the world’s population expands by more than the equivalent of the total number of inhabitants in Australia and Canada combined. Less than 250 years ago, just one billion people were living on this planet. Today, that number has reached nearly eight billion. This represents an annual population growth rate of over 1% and a doubling of the population every 70 years – which is less than a lifetime for many people. Remember this when you complain about overcrowded cities! The Industrial Revolution brought the world machinery to plough, sow and harvest fields – which freed peasants from hard labour on farms, but also transformed smallholdings into industrial operations and signalled the end of the idyllic pastoral scenes immortalized in 19th-century paintings. Since then, those peasants’ descendants have continued to move around in search of work, contributing to the rapid growth of urban agglomerations. The resulting – and ongoing – societal developments have continuously increased the need for highly detailed, accurate and timely spatial data. This ever-evolving landscape forms the backdrop for examining where UAS mapping is now heading.
Persuasion skills
The main spatial data acquisition technologies for detailed 3D mapping of sites are based on imaging devices (photogrammetry) and Lidar sensors (laser scanning). The processing software to extract meaningful information from the data is greatly supported by the achievements of the computer vision research community over the last four decades. The major semi-finished products are point clouds. Cameras and Lidar sensors can be mounted on a wide variety of platforms or carriers, including vehicles and aircraft. Platforms operating outdoors, such as manned aircraft and cars, are usually equipped with GNSS and an inertial navigation system (INS) to accurately determine the six exterior orientation parameters of the sensors (3D position and orientation of the sensors in space). To improve reliability of georeferencing, additional sensors are often used such as wheel counters and compasses. The use of ground control points further enhances the geometric accuracy of the data. Thanks to simultaneous location and mapping (SLAM) algorithms, indoor mapping has become possible using trolleys, backpacks or handheld solutions. The decision for a specific platform depends on the application, size of the survey area, severity of disruption to human activities (e.g. interference with train timetables), required accuracy and level of detail, costs, instruments available at the surveying firms and the ability of those firms to communicate the benefits of their solutions to potential customers.
Miniaturization
On the flip side of societal developments are the technological advances. The key trend in the evolution of UAS mapping can be summarized as the miniaturization of components. Cameras and Lidar sensors suited for capturing high-quality data are becoming smaller and lighter, propped up by advanced processing software which facilitates the use of calibrated metric cameras and heavy Lidar sensors for precision solutions. Today’s positioning and orientation systems (POS) based on GNSS and INS can be held in the palm of one’s hand. The miniaturization of rotors, electric engines and batteries, in combination with carbon-fibre frames, has enabled the construction of lightweight UASs without compromising air stability. On such systems, camera(s) and Lidar (sensors) can be mounted abreast for the simultaneous capture of images and Lidar point clouds. Concurrent capturing of Lidar point clouds and photogrammetric images has proven to be beneficial for 3D mapping of built-up areas.
Hot spots
As illustrated by the numerous case studies published in GIM International in recent years, the UAS has proven its suitability for many 3D mapping applications, including at archaeological sites, industrial complexes, power stations, open-pit mines and construction sites. The use of UASs for capturing such sites will continue to flourish. Particularly, UAS photogrammetry is routinely used for mapping, inspection and monitoring of such sites. The projects concern individual buildings, small areas of interest and other isolated outdoor sites. Vast areas, such as urban agglomerations, are usually three-dimensionally mapped by selecting one geodata acquisition technology (often aerial photogrammetry) for the entire territory. That means all spots are treated equally. However, it is not always a case of ‘one size fits all’; some spots are more equal than others. Choosing one technology based on the greatest common denominator results in a dataset in which some spots are captured at the right level of detail while others are over-detailed or under-detailed. By complementing a UAS with trolley-based, backpack or handheld mobile mapping systems, under-detailed spots can be captured at the desired level of detail.
Circular economy
The ongoing miniaturization of carriers and sensors in conjunction with SLAM algorithms for positioning and orientation purposes has also made it possible for copters to manoeuvre through indoor spaces. Equipped with cameras and/or laser scanners, they can collect high-density point clouds. The high level of detail and accuracy of the data helps facility managers to inspect their property. It also supports the creation of 3D cadastres, which are aimed at recording the ownership of volumetric parts of buildings and other constructions. Authorities and citizens alike are convinced that wasting fuel and other resources as well as the emission of harmful substances should be minimized through reuse, refurbishment and/or the use of alternatives in pursuit of the circular economy. The main consequence is that sites where humans are active, including agricultural lands and mines, need to be mapped and monitored in ever-greater detail. Within today’s industrial agriculture, for example, the collection of spatial data supports regular inspections to avoid waste of fertilizers, fuel, seeds and water. A UAS is well-suited for capturing such spatial data on a regular basis. When it comes to indoor mapping, UAS and mobile mapping complement rather than compete with one another. For example, if used indoors a UAS could collide with objects or people, causing damage and possibly injuries, making it useless in crowded indoor environments. In such a setting, mobile mapping is a perfect solution. In addition, the two platforms have different perspectives (i.e. view angles): sideways-looking versus image capture from above.
Building information modelling (BIM) plays an essential role in the circularity mindset, since information on the types and quantities of construction materials used is key. Such an information system, which is also needed for the inspection and maintenance of indoor and outdoor spaces, could be called a building materials cadastre.
Bottlenecks
Ever since the emergence of computers, it seems to have been a rule of thumb that the amount of data acquired by sensors is ten times as much as the processing capacity of computers – so it’s no wonder that so many researchers are throwing themselves into data science and artificial intelligence to speed up the processing of geodata. Another major bottleneck preventing the rapid introduction of UASs in several applications is that many professionals seem reluctant to replace tried-and-tested technology with a novelty that has a non-proven outcome – even though it may be convincingly cheaper and demonstrably more efficient.
Essentials
There are four essential ingredients determining data quality (i.e. accuracy and detail) in 3D mapping systems: the sensors, the software, the platform and, above all, the survey plan. The design of the survey plan requires thorough knowledge, skills and expertise. This is where the geomatics specialist comes in. Given the strong societal needs for geoinformation outlined above, it is odd that universities in so few countries offer bachelor-level geomatics degrees; at best, the subject is usually on offer at master’s level only. There is a serious risk that society will pay the price for this in the future and be forced to increasingly depend on the less specialized knowledge of the multinational informatics industry.
Author: Mathias Lemmens
13/05/2020