Lidar (Light Detection and Ranging) uses lasers to measure data points that represent the world. The 3D models are used by surveyors for topographic maps, building capture, and more.
An overview of surveying
Surveying has been important for decision-making since ancient Egypt, where it played a key role in tasks like defining property boundaries for tax purposes and managing newly acquired lands.
Originally, surveying was completed using manual methods, such as with rods and chains, compasses, plumb bob and a lot of handwritten calculations to determine relative distances. Today, surveying fundamentals still have a core place in society. We have clients at NavVis who describe that some of their existing processes still rely heavily on graph paper to survey complex buildings.
Technology progressed until photogrammetry arrived, where terrain could be mapped using photos taken from the ground or from the air.
Then, in the late 1990s and especially from 2000 onwards, lidar scanning (LiDAR and LIDAR are also correct ways to write it) started to become the new standard for surveying. An abbreviation for “Light Detection and Ranging”, lidar uses lasers to scan the environment and represent it in the form of numerous data points.
This “point cloud” data collected using lidar is used to create detailed 2D and 3D maps including CAD linework, terrain and contour maps, Digital Elevation Models (DEMs), and various other models and visualizations of streets and buildings. This made it game-changing technology for land surveying.
Introducing lidar technology
An important lidar principle to remember is “time of flight.” The rapid laser pulses sent out from a lidar device bounce off the terrain and back to the sensor. The time of flight is how long it takes this laser pulse to make this round trip.
Knowing the time and the speed of the laser (which is the speed of light), a computer can then calculate the distance the laser traveled (distance = speed x time), which gives us the exact position that the laser bounced off of in the environment.
Note: The angle that the laser records the position from is equally vital to knowing the position for that laser pulse.
Take millions of these measurements, and the result is an accurate model of the environment surrounding the device. The “points of data” that are collected are collectively referred to as a point cloud: Everything you need to know about point clouds. When combined precisely with color data from cameras, a visualization of this data looks like this:
There are three key components of a lidar scanner to be aware of:
- A laser source, which emits near-infrared lasers, sweeping the environment, tracking the angle of the laser and
- A laser receiver recording the reflected laser pulses
- Timing and positioning systems, such as a GPS or IMU (Inertia Measurement Unit).
Types of lidar-based surveys
Lidar scanning equipment can take a wide variety of forms, from devices used on the ground to drones that scan from the sky.
In an aerial lidar survey, scanners are mounted on a plane, helicopter or drone. This allows them to cover a wider area quickly, but it comes at additional cost and typically lower density.
In a terrestrial lidar survey, a terrestrial laser scanner is used, also known as a TLS. This can be in the form of a stationary set-up that is mounted on a tripod, or a mobile solution (commonly known as MTLS or MMS) that is carried by surveyors or mounted on vehicles.
In an example TLS workflow, a surveyor would establish a control network with a total station, laser tracker or GNSS. Once the surveyor returns to the office, they would register the scans together, organize the photos, and generate the deliverables.
A wearable lidar scanning solution like NavVis MLX or NavVis VLX 3 is also somewhat of a combination of the two. These devices capture accurate topographic details of the environment in the form of geo-referenced, photorealistic point clouds and high-definition 360 panoramas at walking speed, and can be used seamlessly alongside a stationary TLS.
Benefits of lidar surveying
Unlike photogrammetry, lidar scanning can be used to create 3D models, works in any light condition, and can penetrate dense features to provide information that photos simply cannot see. It is also a flexible collection method that can be used equally as effectively when surveying stationary buildings , structures, or landscapes.
To summarize, the benefits of lidar are:
- High precision and accuracy
- Speed and efficiency in data collection
- Versatility in various environments and conditions
- Cost-effectiveness compared to traditional methods
When used in combination with simultaneous localization and mapping (SLAM) technology, the benefits of lidar scanning multiply: it becomes even quicker to scan a location, including hazardous areas or those with difficult geometry.
Real-world applications of lidar surveys
Lidar technology can be found in the toolbox of licensed surveyors working on varied projects including (but not limited to):
- Topographic and detail surveys
- Building measurement surveys
- Infrastructure surveys such as road or bridge surveys
A topographic survey, sometimes called a topo or detail survey, maps the boundaries and features of a parcel of land. It produces an accurate map of current topographic conditions, usually as preparation for engineering or construction projects.
A building measurement survey will include various as-built structures, both indoors and outdoors (e.g. façades and courtyards). The resulting digital models and visual representations can serve as references for documentation, restoration, or conservation of heritage sites.
A road survey will map roads but also associated objects (also known as street furniture), such as curbs, signage, lamp posts, and benches.
A survey deliverable might include:
- contour lines
- boundary lines
- natural features
- buildings
They are important in various industries and professions, including:
- Urban planning and development
- Construction and infrastructure projects
- Environmental monitoring and conservation
- Facility management and Building Information Modeling (BIM)
- Government and municipal uses
Lidar surveying outputs
Digital elevation model (DEM): A 3D representation of the Earth’s bare surface, excluding natural features. Indicates elevation values at regular intervals.
Digital terrain model (DTM): A 3D model that augments the DEM with natural features such as rivers, vegetation, etc.
3D building model: A geo-located model that indicates the position, layout, and dimensions of any structures on site.
Computer-aided design (CAD) map: A 2D map that uses points and line drawings to indicate all necessary details and features.
Lidar surveying in action: A case study
Sova Surveys in Bath, England, was contacted by a return client to produce a BIM model of Margam Castle in Wales for a refurb project.
This workflow uses multiple types of lidar scanner, both a stationary TLS and a NavVis VLX, to get the required accuracy but do it at a much higher speed than TLS could manage alone.
They used a total station to set a minimal control network: four external points and five per floor in the interior. Then, a Trimble TLS was used to capture the “spine” of the building, which means connecting spaces like hallways. They also used the TLS to capture areas they planned to model at LOD400, like the central staircase.
To set control for the NavVis VLX scan, they used the Trimble's integrated laser pointer to make markings as they went. “That way, we had all the control we needed, all without having to use the total station again," they reported. Then, it was a simple matter of walking the castle with the NavVis VLX to finish the point cloud and capture comprehensive panoramic imagery.
Read the full case study here: Sova Surveys' scan-to-BIM success at Margam Castle →Tips for choosing a survey scanning solution
Factors to consider when planning a survey include:
- Project size
- Budget
- Timeline
- Accuracy required
- Environment and conditions
The requirements of the project will determine what technology or combination of technologies will be most suitable. Surveyors must consider what challenges they will face in the field. For example, urban topographic mapping might include hazardous or busy areas that make it time-consuming to capture or that make conventional surveying techniques less effective.
Mobile lidar scanners that utilize SLAM technology can overcome or at least mitigate some of these challenges. Premier SLAM-based laser scanning solutions provide high-definition panoramic imagery with laser scanning accuracy . The deliverables can be produced faster and with more flexibility than with a TLS.
When integrated into topographic workflows, SLAM-based laser scanning complements and enhances surveying methods such as static laser scanning and total stations, offering a more efficient and comprehensive approach to terrain data capture.
Learn more about lidar surveying
NavVis offers SLAM-based, wearable laser scanning solutions to empower surveying and reality capture professionals to capture accurate data, visualize it effectively, and integrate it into existing workflows. Find out more on our surveying and reality capture page.
Alternatively, contact us today to learn how our professional lidar survey technology can provide you with accurate, high-resolution data tailored to your specific needs. Request a free consultation now and see the difference lidar can make.