LiDAR Topographic Surveying in No-Fly Dense Urban Areas: Flexible and Safe Measurement Methods

Table of Contents

• Why drones can’t be flown in dense urban areas and surveying challenges

• What is topographic surveying using LiDAR

• Benefits of LiDAR surveying in urban areas

• Flexibility and safety of ground-based LiDAR as a drone alternative

• Efficient surveying by combining GNSS and LiDAR

• LRTK LiDAR enables flexible, safe, and simple surveying

• FAQ

In densely populated urban areas, aerial surveying using unmanned aircraft such as drones is restricted for legal and safety reasons. However, the need to obtain high-accuracy topographic data in urban areas for purposes such as road maintenance and disaster prevention still exists. So how can we conduct efficient and safe topographic surveys where drones cannot be flown? This article focuses on laser measurement technology (LiDAR) as a solution and explains in detail flexible and safe surveying methods that perform well in urban environments.

Why drones can’t be flown in dense urban areas and surveying challenges

First, in urban population-concentrated areas (so-called DID zones), unmanned aircraft like drones cannot be freely flown due to law. Under Japan’s Aviation Law, airspace over areas where people are concentrated is designated as “no-fly airspace,” and flying drones without special permission is generally prohibited. The rationale behind this regulation is to prevent risks to people and buildings on the ground from crashes caused by equipment failure or operator error. In practice, urban areas contain many people and structures in confined spaces, so drone flights always carry concerns about accidents and privacy infringement. In Japan’s major metropolitan areas, many regions — including the 23 wards of Tokyo, Yokohama, and Osaka — fall under these populated area designations (DID), making drone surveying over city areas practically very difficult.

When conducting topographic surveys in dense urban areas where drones cannot be used, one must rely on conventional ground surveying. But city-specific conditions — narrow roads and clusters of high-rise buildings — present several challenges to traditional methods. For example, the abundance of buildings often degrades satellite positioning (GNSS) accuracy. Also, detailed point measurements using total stations require many personnel and time, and surveying work on busy roads itself becomes a safety risk. Moreover, even when using conventional ground-based laser scanners, each scan must be set up on a tripod at a single location, requiring repeated equipment relocations to cover complex urban terrain. Thus, while drone-based efficient surveying is unavailable in no-fly urban areas, conventional methods have limits in speed and safety.

What is topographic surveying using LiDAR

LiDAR (Light Detection and Ranging) is a technology that measures distance by emitting laser light at a target and measuring its reflection. In surveying, LiDAR is used as a “3D laser scanner” and is notable as a method that can measure surrounding terrain and structures in a surface-wise manner. Whereas conventional surveying measures height and position point by point, LiDAR surveying fires countless laser pulses to produce a collection of points (point cloud data) that records terrain shapes in detail. This makes it possible to digitally capture ground undulations, building and road positions as high-density point clouds.

LiDAR topographic surveying can be performed by mounting scanners on aircraft or drones to measure large areas from the air, or by using ground-based equipment to scan the surroundings. Airborne LiDAR is suitable for wide-area surveys, while ground LiDAR is suitable for localized detailed measurements. In either case, point cloud data from LiDAR surveying can be used to create topographic maps and cross sections, calculate elevation differences and volumes, and support a wide range of applications from civil engineering and construction to urban planning and disaster prevention. In urban areas in particular, LiDAR is highly effective because it can digitize complex structures and intricate terrain in a short time.

Benefits of LiDAR surveying in urban areas

One of the biggest advantages of using LiDAR surveying in urban areas is improved efficiency. Traditionally, many survey points had to be measured painstakingly to create topographic maps, but LiDAR scanning can acquire wide-area point cloud data in a short time. For example, installing a laser scanner along a road and scanning while driving or walking can record surrounding ground surfaces and building shapes at once, allowing an area that would have taken days with conventional methods to be surveyed in just a few hours. This efficiency is a major advantage for urban construction planning and investigations that require results within limited timeframes.

Improved safety is another key point. LiDAR surveying measures the surroundings non-contact, reducing the risk of surveyors entering roadways and facing danger. Because surveys can be completed without closing roads or imposing traffic restrictions, the impact on third parties is minimized. Since lasers can measure from a distance, data for high places or areas difficult to access by people can be obtained safely. For instance, at busy intersections or on steep slopes and cliffs, LiDAR equipment can be operated from sidewalks or other safe positions to measure terrain, contributing to worker safety.

Furthermore, point cloud data obtained by LiDAR are detailed and comprehensive. The entire site can be captured as a 3D “digital copy,” making it easy to measure dimensions later or extract cross sections for secondary use. In complex urban sites where missing or overlooking measurements is a challenge, LiDAR can digitize almost all objects in a single scan, reducing the need for return site visits. In this way, LiDAR topographic surveying in urban areas brings significant advantages in speed, safety, and thoroughness of the resulting data.

Flexibility and safety of ground-based LiDAR as a drone alternative

In environments where drones cannot be used, ground-based LiDAR measurement is an effective alternative. Ground-based LiDAR refers to laser scanners mounted on pedestrians or vehicles to scan the ground and surroundings. This allows data acquisition directly on-site in places drones cannot reach — narrow alleys, under roofs, or behind bridges. Because ground measurements are not subject to aviation law restrictions, they can be conducted nimbly in populated areas without permit procedures. Moreover, equipment that can scan while moving on the ground allows flexible changes to measurement routes or additional scans as site conditions require, enabling adaptable response to complex urban terrain.

Some ground-based LiDAR units use SLAM (Simultaneous Localization and Mapping) technology, allowing autonomous positional estimation and scanning even in indoor or underground spaces where GPS signals don’t reach. The ability to choose appropriate measurement methods according to the environment is another strength unique to ground-based surveying.

From a safety standpoint, ground-based LiDAR has significant advantages. Because no object is flown in the air, equipment malfunction poses no risk of falling debris harming people or buildings. Also, equipment can be operated relatively safely on the ground at night or in adverse weather (laser measurements themselves can be performed day or night as long as visibility is sufficient). In urban areas where surveys are sometimes desired during early morning or nighttime when foot traffic is low, ground-based LiDAR’s quiet operation and limited light dispersion make it easier to perform measurements late at night while minimizing impact on the surroundings. Thus, LiDAR surveying from the ground is a safe measurement method that can be flexibly applied in city areas without flight risks.

Efficient surveying by combining GNSS and LiDAR

To maximize the power of LiDAR surveying, integration with GNSS (satellite positioning) technology has progressed in recent years. Systems that combine high-accuracy GNSS receivers (RTK methods, etc.) with mobile laser scanners can attach coordinate information to point cloud data in real time during measurement. Previously, post-scan alignment to control points and integration of multiple scans were required, but GNSS enables acquisition of absolute coordinates during scanning, greatly reducing troublesome post-processing. The ease of obtaining map-coordinate point clouds immediately without installing markers or control points is a very practical advantage.

GNSS-integrated LiDAR equipment also enables large-area, high-accuracy surveying in a short time. For example, a unit combining GNSS-RTK positional corrections with a high-performance laser scanner can accurately measure buildings and terrain several hundred meters ahead, allowing a single operator to scan sites of several hectares in about an hour. Because multiple scans obtained are already in the same coordinate reference, separate point clouds automatically overlap and do not produce misalignments when joined later. Field-acquired data can be uploaded to the cloud immediately and shared with stakeholders, or distances, angles, and areas can be measured on the web without specialized software, contributing to overall surveying process efficiency.

LRTK LiDAR enables flexible, safe, and simple surveying

One example of a measurement solution that brings together the technologies described above and dramatically simplifies topographic surveying in no-fly dense urban areas is LRTK LiDAR. LRTK LiDAR is a domestically produced surveying instrument that integrates a high-accuracy GNSS receiver and a high-performance 3D laser scanner, developed with a strong focus on ease of use on site. Scanning can be started without the hassle of placing markers, and the acquired point clouds are automatically tagged with latitude, longitude, and elevation information. Because the system is operated via a tablet and scan status can be confirmed in real time, even first-time users can thoroughly record the intended area. Objects that used to be easily overlooked, such as thin utility wires, can be captured precisely in the point cloud, and acquired data can be uploaded to the cloud on site and shared with stakeholders immediately.

With LRTK LiDAR, a single operator can safely complete topographic surveying even in urban sites where drones cannot be flown. Its flexibility and mobility make terrain measurement possible in any situation — from roads and narrow sites to under bridges and among high-rise buildings. The LRTK solution, which lowers the barriers to complex urban surveying, will be a reliable ally for obtaining precise data “quickly, safely, and simply” in future surveying work. This next-generation measurement approach is transforming surveying sites into more efficient and safer environments.

FAQ

Q: Why are drones regulated in urban areas? A: Drone flight over urban areas (population-concentrated districts) is generally prohibited under the Aviation Law. If a drone crashes in densely populated areas, it can cause significant damage to people and buildings on the ground. From a safety perspective, permission from the Ministry of Land, Infrastructure, Transport and Tourism is required to operate drones in urban areas.

Q: What data does LiDAR surveying provide? A: LiDAR produces large numbers of points known as “3D point cloud data” obtained by laser. These point clouds reflect the shapes of the ground and structures in detail and can be used to create contour maps and longitudinal/cross-sectional drawings, measure land elevation, distance, and slope, and even generate 3D models. Unlike photogrammetry, LiDAR provides objective spatial data that can be acquired in shadows or at night.

Q: What accuracy and measurement range can ground-based LiDAR achieve? A: It depends on the device, but high-performance ground-based LiDAR can achieve positional accuracy on the order of a few centimeters (a few inches), and range-direction resolution below a few centimeters (below a few inches). The measurable distance (laser reach) depends on the scanner’s laser power; typical ground scanners can acquire data from tens of meters (tens of ft) to, in long-range units, hundreds of meters (hundreds of ft). For example, LRTK LiDAR can capture point clouds of targets about 200 m (656.2 ft) away, allowing measurement of upper parts of buildings or entire plazas from the ground in a single scan.

Q: Can LiDAR be used without specialized knowledge? A: Modern LiDAR systems are designed to be user-friendly, and with basic operation training, even those with limited surveying experience can handle them. Devices like LRTK LiDAR that allow real-time point cloud confirmation make it easier to collect complete data, enabling anyone to conduct measurements with confidence. However, interpreting acquired data and compiling survey deliverables may still require a certain level of civil engineering and surveying knowledge.

Q: How much faster is surveying compared to traditional methods? A: It depends on site scale, but as a rough comparison, using LiDAR can shorten surveying time to a fraction — from several times faster to an order of magnitude faster — than manual surveying. For example, sites of several hectares that would take days to measure with a total station may be nearly completed in under half a day with high-speed LiDAR scanning. Reduced post-processing burden also shortens overall project timelines from planning to deliverable production.

Q: Is processing and using point cloud data difficult? A: Because point cloud data contains a lot of information, high-performance PCs and specialized software were traditionally required. However, cloud platforms for visualizing and editing point clouds are becoming widespread, making basic measurements and drafting possible via a browser without dedicated software. Tools like the cloud viewer provided by LRTK allow uploaded field scans to be shared and for plan and cross-section work to be efficiently performed on office PCs. Point cloud data can also be exported in standard formats such as LAS or PLY, which are highly compatible with other CAD and BIM tools, facilitating integration into conventional design workflows.

Q: Isn’t equipment expensive to introduce? A: Historically, 3D laser scanners were large and very expensive, but recent technological advances and wider adoption are bringing costs down. Compact, lightweight surveying devices that utilize smartphones, such as those in the LRTK series, have appeared and can be introduced at lower cost than traditional equipment. Some products also combine photogrammetry and laser surveying capabilities, making them more versatile and often more economical than purchasing multiple surveying instruments. Although initial investment is required, the resulting labor cost savings and shorter construction periods mean the investment can be recouped, making it a sound overall investment.

Q: What sites and uses are suitable for LiDAR surveying? A: LiDAR is highly effective at sites with complex terrain or structures, such as urban roads and blocks, 3D records of aging infrastructure, and disaster site assessment. It is suitable for detailed recording of small areas; for very large areas on the order of tens of square kilometers, combining aerial photogrammetry or airborne LiDAR may be preferable. Generally, LiDAR surveying is useful whenever precise 3D data of site terrain and structures is desired — from civil engineering design to urban planning, disaster mitigation, and cultural heritage documentation.

Q: How does photogrammetry differ from LiDAR surveying? A: Photogrammetry reconstructs 3D shapes from images taken by cameras using software, while LiDAR directly measures distances with lasers to obtain 3D point clouds. Photogrammetry is easy and can capture wide areas at once, but achieving high accuracy may require many control points and good lighting. LiDAR can obtain stable distance data in shadows or at night and captures shapes regardless of surface texture or pattern. Photogrammetric processing can take considerable time, whereas LiDAR point clouds can often be used immediately as survey deliverables. Both have strengths and weaknesses and are chosen based on use; recently, solutions like LRTK Phone that combine photogrammetry and LiDAR have also appeared.