Optimizing Laser Scanning Techniques for Heritage Site Preservation: A Case Study Using the BLK360 G1
ABSTRACT
This article discusses the application of laser scanners with different settings in scanning, documenting and potentially preserving cultural heritage sites. Using the Leica BLK360 G1 laser scanner, we outline our methodology, including settings, scanning points, and distance considerations. We also provide insights into the registration and processing of scan data, compare different scanning results, and offer conclusions on the optimal settings for achieving the best balance of quality and time. Finally, we suggest potential future comparisons with the BLK2GO mobile scanner and RTC360 static scanner.
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1. INTRODUCTION
1.1. About our past and present work
Our team has a long history of using advanced technologies to document, scan and preserve cultural heritage sites. In the past, we have used various methods, including photogrammetry and laser scanning. Notable projects include the detailed documentation of the Teleki-Bolyai Library in Targu Mures, Romania or the architectural survey of Wesselényi Castle in Jibou, Romania. These projects have set a solid foundation for our current work, emphasizing accuracy and efficiency in heritage documentation.
Before surveying a site, we conduct comprehensive research to ensure project completion according to specifications both from a historical values and a technological perspective. We always choose the best scanning settings and methods for optimal results. However, our findings often lack a solid research reference for methodology due to the experience-based nature of this technology and varying site conditions. In this article, we will share our experiences and guidelines on setting up a scanner for achieving the highest quality scans in the shortest possible time.
1.2. BLK 360 g1
In this research we are using the Leica BLK360 G1. This device is a compact and powerful laser scanner that has been a good companion on our approach to scanning. With its ease of use and high-quality output, the BLK360 G1 allows us to capture detailed 3D point cloud data quickly and accurately. This device is particularly advantageous for its portability and cost-efficiency, making it suitable for diverse site conditions, shown on Figure 1.
According to the user manual, the BLK360 has a 3D point accuracy of 6 mm at 10 meters, 8 mm at 20 meters, and a maximum range of 60 meters, with a scan rate of up to 360,000 points per second. The scanning time varies based on density: 40 seconds for low density, 1 minute 50 seconds for medium density, and 3 minutes 40 seconds for high density. Additionally, the LDR mode takes 1 minute, while HDR mode requires 2 minutes 30 seconds.
1.3. the research
In this study, we aim to assess the effectiveness of the BLK360 G1 in scanning a specific cultural heritage site. We will detail our methodology, from the initial settings and scanning points to the final registration and processing of the data. Our goal is to determine the best practices for using the BLK360 G1 for scanning cultural heritage and for preservation projects. This research is exclusively focused on BLK360 G1 settings. Comparison between other scanners will be done shortly.
2. METHODOLOGY
2.1. Scanning
Our methodology is primarily based on practical experience. Surveyors typically learn the basics and gain expertise by working on various projects, which aligns with the normal learning curve in the field. In this research, we aim to provide a broader perspective on the use of different scanner settings, enhancing understanding and application in diverse scenarios.
2.1.1. Settings
Leica’s software for data management, the BLK Data Manager (Figure 2.), is a small and easy-to-use application. It allows users to change scanner settings, download or delete scans from the scanner to a PC, and check battery percentage. In this research, we are experimenting with all variations of the scan density and image quality settings to determine the optimal configurations.
For this project we exclusively use the data manager, and direct IP address connections to the scanner are not utilized.
Setting up the BLK360 involves configuring several parameters to ensure optimal data capture. These settings include the resolution, scanning speed, and exposure settings, which need to be tailored to the specific conditions of the site. The BLK360 G1 offers six possible settings for scanning: low, medium, and high scan density, combined with either LDR (Low Dynamic Range) or HDR (High Dynamic Range) image quality.
2.1.2. Setup Locations
Identifying strategic locations for scanning is crucial for comprehensive coverage of the site. We selected these setups to minimize shadowed or covered areas and ensure that all relevant details are captured. Due to the site’s design, identifying these setups was challenging, because of the trees and vegetation. Despite this, we identified the three points shown in Figure 3, where we conducted the research.
2.1.3. Scanning distance
Maintaining an appropriate distance from the building is essential for accurate data capture. We analyze the site’s layout to determine optimal distances, balancing the need for detail with the scanner’s range capabilities. The main question is how far away one can be to use the shortest scanning settings and still achieve the best results. Throughout the research, we conducted all scans from the three points shown in Figure 3, ensuring we tested various distances to identify the most effective settings. The three setups were positioned at distances of approximately 8.5, 13, and 29 meters from the base of the facade, shown on Figure 4. In the article, we will consistently refer to them as setups (from left to right) 1, 2, and 3. This range of distances allowed us to evaluate the performance of the scanner settings at different proximities, helping us determine the optimal configuration for achieving high-quality scans efficiently.
2.2. SITE
2.2.1. About the site
While writing this article, the scanned building was already renovated, and the street was partially closed to traffic due to the reorganization of the surrounding area.
The selected cultural heritage site is a historically significant building with intricate architectural details. Its preservation is critical, and detailed documentation will aid in future restoration efforts.
The Palace of Culture (Romanian: Palatul Culturii, Hungarian: Kultúrpalota) is a historic building in Târgu Mureș, Romania, housing the Mureș County Library, Museum, and State Philharmonic. Built between 1911 and 1913 under Mayor György Bernády, it features Art Nouveau architecture with three sections. Highlights include the Mirrors’ Hall, a 700-seat Concert Hall, and a Small Hall for events. Decorative elements include Hungarian legend scenes, bronze portraits, and colourful Zsolnay roof tiles. The building is listed in the National Register of Historic Monuments.
2.2.3. Difficulties
Scanning cultural heritage sites often presents challenges, such as limited access to certain areas, varying light conditions, and the presence of obstacles. These factors require careful planning and adaptation of scanning strategies.
In this research, we only scanned the façade of the building. Despite some complicating factors such as trees, high traffic in some areas, and opening and closing doors, we successfully captured the necessary data. These challenges required careful planning and strategic placement of scanning points to ensure comprehensive coverage while minimizing interruptions and obstructions.
2.3. REGISTRATION AND PROCESSING
2.3.1. Software
We use Leica’s specialized software, Cyclone REGISTER 360 PLUS, for the registration and processing of scan data. This software enables us to align multiple scans, clean the data, make measurements, add geotags, and more. Its well-designed user interface shown on Figure 5, ensures smooth post-processing, enhancing our workflow and efficiency.
2.3.2 Steps of registration and processing
- Data Import: Importing the raw scan data into the software.
- Registration: Aligning the individual scans to create a unified model.
- Cleaning: Removing noise and irrelevant data points.
- Quality checking: Ensuring the accuracy and completeness of the model.
- Export: Exporting the point cloud in needed formats.
3. RESULTS
The results section will present the final point cloud of the cultural heritage site, showcasing the level of detail captured and the scanning time. This visualization will illustrate the accuracy and efficiency of our scanning process and will compare the different scans.
Throughout the scanning process, we measured the following times for different settings:
- Low scanning density + LDR: 1.40 minutes
- Low scanning density + HDR: 2.45 minutes
- Medium scanning density + LDR: 2.54 minutes
- Medium scanning density + HDR: 4.13 minutes
- High scanning density + LDR: 4.43 minutes
- High scanning density + HDR: 5.55 minutes
If LDR quality is chosen, see Figure 6, the bright and shadow areas can become overly bright or too dark. However, during our scan, the weather was perfect for using LDR due to the cloudy sky, which provided evenly diffused lighting.
Compared to the LDR image in Figure 6, it can be concluded that in Figure 7, bright and dark contrast is more prevalent.
This scan was made from point 1 which is 8.5 metres from the base of the building and the scanning time for LDR was 1.40 minutes and for HDR 2.45 minutes, and scanning details remained the same. This is perfect to show the differences between the LDR and HDR image quality. A difference of 1 minute and 5 seconds between the two scans may seem brief, but over the course of 200 or more scans, this time discrepancy becomes significant. Now we will show the differences between the scanning density.
In Figure 8, we observe the differences between the three points. Our conclusion is that for most applications low scanning density is not the optimal choice for scanning an intricate façade with ornate details from these distances.
In Figure 9 we observe that broadly the façade can be seen in a much better quality, but the details are still not very visible. The LDR scanning in medium density took 2.54 minutes, we note that it is 10 seconds more than the low density HDR which is almost insignificant but the medium HDR is 4.13 minutes.
In Figure 10, it can be concluded that high-density scanning is the most effective approach for exterior scanning, especially for capturing this very ornate façade and its many ornaments. However, the details captured in the scan from point 3 are somewhat less visible. The high-density LDR scanning took 4.43 minutes, which is 30 seconds longer than the medium HDR scan, while the high HDR scan lasted 5.55 minutes.
To enhance observation, we have included close-up images in Figure 11 to highlight the quality of the details. The details are less visible at greater distances. Ideally, the best approach would be to conduct scans at close range and, if possible, from the same height.
In Figure 12, we have included close-up images of the same details captured from the same distance but with different scanning densities. The differences among the three images are quite significant. While the low-density scan is nearly invisible, the medium-density scan is somewhat visible but not entirely clear. In contrast, the high-density scan clearly represents the details and is undoubtedly the best quality.
In Figure 13, we present another example of high-density scanning from various distances. It is important to examine details from different orbital angles because while the scanner’s viewpoint might capture the best possible details, other angles might reveal missing information. Clearly, if scans were conducted from additional angles, there would be fewer missing details.
4. CONCLUSION
4.1. What is the best setting for each location - quality/time
Based on our findings, achieving the highest quality scans in the shortest time requires customization according to the type of heritage site and prevailing weather conditions. Our research was conducted exclusively on exterior surfaces under cloudy conditions.
Scans should be tailored to the client’s needs. For some projects, the exterior of a building may be less critical than the interior, and capturing only the outer lines and structure may be sufficient to align with the interior details. However, for scanning cultural heritage sites where the exterior is significant, we recommend using high-density scanning with HDR quality, which takes 5.55 minutes. Although this may seem time-consuming, it is crucial for producing a clear and detailed scan.
In better weather conditions, LDR scanning might be adequate and faster, taking 4.43 minutes. If site conditions allow for closer scanning and consistent height, medium-density scanning with LDR quality, which takes 2.54 minutes, could be sufficient. However, this approach requires more scanning points, potentially increasing overall scanning time.
Low-density scanning is generally not suitable for exterior surfaces where detail is crucial. However, for interior scanning, low density can be more appropriate due to the shorter distances but note that higher number of scanning points may be needed. If interior lighting conditions are favourable, low-density scanning with LDR quality could be a viable option, with a scanning time of only 1.40 minutes.
In conclusion, scanning approaches should be tailored to the specific conditions of the site and the client’s requirements. Our research provides a clearer understanding of how different scanning methods and conditions impact the quality and efficiency of the scans.
4.2. Future Comparions
Looking ahead, we propose a future study to compare the BLK360 G1 with the BLK360 G2, BLK2GO, BLK2FLY and RTC360. This will help refine our documentation techniques as well as demonstrate the many factors that need to be considered when 3D scanning a building. Field experience with these factors provides our team with the know-how needed to deliver consistently good results in built heritage preservation and adaptive reuse. Additionally, a future study could explore methodologies for processing the point cloud, including techniques for cleaning, as illustrated in Figure 14.
Cleaning the point cloud is essential for emphasizing the main subject of the scan. It is often necessary due to site conditions, such as moving objects, people, or other obstructions that may cover important parts of the site. However, in some cases, cleaning may not be as critical.
Lastly, we want to emphasize that this research is specifically tailored to the BLK360. However, for a unique and historically significant site like the Palace of Culture in Târgu Mureș, we recommend using a more advanced scanner, such as the Leica RTC360 3D Laser Scanner.
The Leica RTC360 is designed for fast and highly precise 3D scanning. With its advanced automatic point cloud registration, high-speed scanning capability of up to 2 million points per second, and the ability to capture full-dome HDR imagery in less than two minutes, it is an excellent choice for capturing intricate details and complex geometries in a cultural heritage site like the Palace of Culture. This scanner ensures that every aspect of the building is documented with exceptional accuracy and clarity, making it ideal for preserving such a valuable architectural gem.
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