Land and Impact Survey and Mapping Technologies

What is Photogrammetry?

Photogrammetry is the science of making measurements from photographs for recording the exact positions of surface points in order to produce a 3D map. It is a technique that has been used for decades by professionals such as surveyors, archaeologists, and cartographers.

Photogrammetry has historically been an exhaustive, time consuming process, now, it's available to everyone with the advancement of techniques and technology! Drones have radically changed things, both by allowing for thousands of aerial pictures to be taken of a single site in one flight , and also because new technology has been developed to help integrate all of those photos into a single 3D map.

What is Lidar?

Lidar stands for “Light Detection And Ranging."

Lidar is a 3D mapping technology that uses lasers to scan and create a 3D map of the surveyed location. It is used in many industries, including construction, mining, and forestry. Lidar is an acronym for “light detection and ranging.” You will often hear “3D” used with Lidar because Lidar provides a 3D mapping of its scan.

Lidars emit pulsed light waves into a surrounding area. The wave bounces off of objects, and when it does so the device will calculate the distance of the surface based on the time it took for the wave to reach the object. This is a great tool for measuring distances in a variety of settings, such as construction sites or even in your own home. It is now used for almost every industrial survey and physical data capture.

PHOTOGRAMMETRY VS LIDAR

Photogrammetry and Lidar are similar but offer different benefits and drawbacks. Photogrammetry provides a photo-like image showing clear details of the exact objects on the ground and their space, size, and color – but because photogrammetry uses photos and not lasers there is a drawback here because lasers can break through tiny spaces like between leaves and trees where some lasers will even hit the ground giving a lot more precise data on certain areas such as forests and areas of high vegetation.

Lidar also has an upper hand when it comes to processing time, full resolution photogrammetry processing can take several hours or even days depending on the size of the project. Lidar on the other hand uses real-time kinematic positioning (RTK) during flight or post-processed kinematic position (PPK) after flight and these fully processed data sets can be ready in as little as under an hour.

When it comes to surveying, there has been an ongoing argument about the comparative values of photogrammetry and LiDAR, and which is best.

So how do you know whether to use LiDAR or photogrammetry?

In general, the rule of thumb is that photogrammetry is good for surveying large sites that aren’t obstructed by tree cover or other impediments, while LiDAR is good for smaller, obstructed sites.

LiDAR should be used when:

You are mapping below tree canopy, mine site conveyors, and other obstructions because photogrammetry has trouble generating elevation models in areas where objects block the ground.

You are modeling narrow objects such as transmission lines, pipes, sharp-edge features (for instance roof edges), and fields of rocks (aggregates) because alternate mapping methods such as SfM algorithms and DIM have lower “conformance” than LiDAR, and thus result in a lower quality of detail in the 3D map produced.

Photogrammetry should be used when:

You are imaging bare earth mine sites, earth works projects, and other areas that are not occluded by trees, buildings, or equipment.

You are performing a small mapping project and photogrammetry data will suit your needs.

Despite all of this, the general advice is that if you’re using LiDAR, you should also use photogrammetry. The logic is that LiDAR is the more expensive of the two options, and since photogrammetry will provide additional useful data, you may as well do both.

However, new LiDAR technology may turn some of this advice on its head. After all, the cheaper and more available LiDAR for drones becomes, the more we will see adoption.

Lidar Applications – Surveying

Lidar applications are endless, common industries in which lidar surveying may be used include but are not limited to the following; civil engineering & surveying, infrastructure such as highways and road networks, and mines & quarries.

CIVIL ENGINEERING & SURVEYING

Usage of Lidar in Civil engineering is extensive. Aspects of civil engineering that require lidar are design, evaluation, and surveying. Lidar can help make decisions on accurate design plans, help to find changes to previous data, and create detailed 3D landscapes for existing structures and vegetation.

Other benefits of surveying with done Lidar include speed, accuracy, and safety. These benefits are self-explanatory – with the efficiency, you get when using a lidar-equipped drone you’re able to cut down on the time it takes to survey massive areas of land, and in effect reduce the budget required as well. Lidar provides an ultra-accurate representation of the environment because of the precision of lasers used in commercial lidar scanners. UAVs make it much safer to run surveying missions that are unmanned and leave virtually no risk for human injury or death.

INFRASTRUCTURE: HIGHWAYS AND ROAD NETWORKS

Lidar is also an extremely important technology for the infrastructure industry. Lidar helps to cut down timelines and budgets for infrastructure planning, maintenance improvement, and development extensively.

When considering infrastructure you have to think about planning road projects, maintaining existing roads, improving existing roads, and developing new roads – within each of these steps of infrastructure Lidar can be used to safely and efficiently collect accurate data that helps to plan new projects, find damaged areas for very necessary repairs (that may be hard to spot with photogrammetry), and much more.

MINES AND QUARRIES

Lidar used in mines and quarries is a critical surveying tool. By nature, mines and quarries are very remote and access is limited making it very dangerous to access. UAV Lidar offers a comprehensive surveying option that is many times more practical than traditional surveying. Like other industries using UAV lidar technology improves safety, speed, and budget. UAVs allow for quick access to hard-to-reach locations while maintaining safety for the operator. Also, this makes it much faster to get the job done – quicker work means fewer resources, less man-hours, and fewer materials needed, this lowers necessary budgets to complete these projects.

Archaeology

One of the most noteworthy (and just plain cool) uses of LiDAR is in helping archaeologists discover new ruin sites, as well as helping them to better understand existing sites.

In many cases, archaeologists may not want to dig at an existing site because they don’t want to risk destroying the ruins that are currently preserved under earth and sand—but LiDAR can allow them to get a view into what is there without having to dig at all.

Check out this video from the Smithsonian explaining how LiDAR was used to reveal a hidden city at Angkor Wat:

How LIDAR Scans Reveal Angkor's Hidden City

Watch this video on YouTube

Earlier this year the Smithsonian reported on the use of LiDAR to research 430 miles of jungle in the El Mirador basin, a vast area in Central America rife with remnants of Mayan civilization that includes huge roads and networks of temples, which was first discovered by using LiDAR data.

Without LiDAR, El Mirador may have never been found, or at least not in its full totality—which is significant, because the discovery of the ruins in El Mirador indicate a high level of cultural and technical sophistication at a much more ancient time than current archeological theories had theorized for the Mayans, and subsequently has led to a general rethinking of our understanding of the entire Mayan world.

Agriculture

LiDAR helps farmers to find areas where costly fertilizer is being overused, and also helps to create elevation maps of farmland that can be converted to create slope and sunlight exposure area maps.

Layer information provided via LiDAR can be used to create high, medium, and low crop production area maps, and extracted data can help farmers to save on fertilizer, and generally optimize their efforts.

Industrial Surveying and Mapping

LiDAR is used in various industrial applications to create 3D maps for:

Stockpile measurements

Mining operations, including the measurement of ore volumes for mining

Topographical mapping for large industrial projects and building projects

Tracking resources

Measuring roadways under traffic (i.e., while cars are driving on them)

It’s important to note that, when it comes to industrial applications, LiDAR is often used in conjunction with photogrammetry—scroll down for an in-depth comparison of the two.

Conservation

LiDAR helps produce accurate maps for conservation efforts, and many U.S. states have undertaken intensive data collection efforts to better document their natural resources so that they can better protect them.

The Iowa Department of Natural Resources, for example, uses LiDAR data to inform their Geographic Information System (GIS), a repository of information about all of the natural resources in the state.

Forestry is one area of conservation where LiDAR has been used to measure canopy heights, biomass measurements, and leaf area.

lidar-drones-conservation

Image source

Water conservation is another area in which LiDAR data has been used to map culverts, flood plains, watersheds, and areas of inundation and depression (i.e., where flooding and drought occur / might occur in the future).

LiDAR data, including derivatives like contour maps, digital elevation models, hillshade projections, and others are assisting with a wide range of natural resource conservation applications.

– University of Minnesota Water Resource Center

Dune monitoring and other related monitoring of natural resources can also be done via LiDAR, and some national parks are starting to allow investigations into the use of drones to map and model the movements of dunes.

iDAR drones vs. ground-based LiDAR

One additional question company leaders must ask themselves when deciding whether to use LiDAR drone systems, is whether they would be better served with LiDAR modules based on the ground. These land-based options, from providers including Faro and Trimble, are highly accurate, delivering millimeter-level scanning.

The downside to using LiDAR on the ground is a lack of efficiency. Flying a drone over a site allows surveyors to accomplish more work in less time, while also reaching hard-to-reach areas, compared to the sometimes tedious process of operating ground-based laser scanners.

As long as an organization can tolerate an accuracy of +/- 5cm when creating 3D models from point clouds, aerial sensors mounted on a LiDAR drone provide a far more efficient approach to mapping and surveying.

LiDAR drones in action: Top use cases

Adding LiDAR UAVs is a great way for companies of all industries to map and survey more effectively. It’s impressive just how many unique deployment scenarios support drone LiDAR technology. Some of these cases can also incorporate photogrammetry, while others are wholly new and driven by the advent of affordable LiDAR drones.

Land surveying for small plots

Whenever there is a need to carry out an accurate aerial survey of a plot of land, a LiDAR drone can be the ideal tool. While a large plot of land may be more suited to a fly-over with a plane or a manned helicopter, drone technology is ideal for small plots.

LiDAR point cloud of a parkEasily construct accurate terrain maps to make informed landscaping decisions. Image by LiDARUSA

Using a drone as a surveying tool is more affordable than commissioning, staffing and fueling a standard aircraft. Furthermore, drones use a small UAV. which doesn't require pilots to fly over the site, making it a safer option. A few operators stationed on the ground can quickly and methodically map out the area and move on.

Topographic and bathymetric surveying

In addition to smaller surveys, LiDAR drones can use sensors to take in large topographical areas, taking over work that would traditionally be carried out from planes or helicopters. In the case of a land-based survey, the drone uses a near-infrared laser.

By flying over the water and using a water-penetrating green light, LiDAR drones can also collect readings about the depth of the sea floor or riverbed in a given area. When creating maps that incorporate bathymetric data, LiDAR drones can cover both the land and the sea.

Digital terrain modeling in advance of work

When companies are in the process of preparing for major dirt-moving work, it's important to have a map of the site in 3D. This is where an accurate digital terrain model (DTM) — created via a LiDAR 3D point cloud — can be pivotal.

True-Color Point CloudsTrue-color point cloud captured by the Zenmuse L1

Dirt-moving is generally paid for by the yard of earth excavated, which means that for budgetary planning purposes, businesses need to know exactly what they are dealing with in a given area, using 3D imagery. LiDAR can penetrate vegetation and other features to give accurate readings about the topography of a given site.

Accident scene mapping and reconstruction

Drones of all kinds are becoming more popular in public safety — for instance, thermal drones can search for missing persons, even at night. In the case of LiDAR drones, the technology is ideally suited to complex accident scene reconstruction. Crews can carry out this work at any time of day, because LiDAR does not require light to work.

Collision Reconstruction LiDARCollision reconstruction in low-light conditions with LiDAR

After the highly accurate 3D model is captured, crews can clear the wreck scene. This timeliness is especially important when an accident site is obstructing traffic. The data from the LiDAR drone can then serve as evidence in any court cases stemming from the crash. Please note that photogrammetry is also an excellent option for crash scene reconstruction and emergency mapping, which you can learn more about in our Emergency Mapping Guidebook below.

Emergency Mapping Guidebook - Desktop CTA

Forestry

Measuring the inventory of a forest used for syrup, pape, or lumber production can be difficult or time-consuming because of the large areas involved. Companies that don't use LiDAR drones may have to rely on estimates based on workers' guesses.

LiDAR Foliage PenetrationLiDAR can measure canopy heights and tree density

A LiDAR drone can not only give accurate readings of metrics such as canopy height and tree density, the sensors involved are precise enough to give readings about individual trees. LiDAR drones can even function in low light when visibility is limited.

Precision agriculture

Basing agricultural practices on precise data has become more popular in recent years, with photography drones helping with everything from crop planning to herd tracking. LiDAR drones can add a new level of accuracy to projections, allowing farmers to respond to conditions in their fields.

One major use of LiDAR drones in agriculture is providing 3D terrain data, which allows operators to construct levees in their rice fields. Another use is to measure the progress of crops, letting farmers use fertilizers in a more targeted fashion.

Power line inspection

While utility operators may have struggled to measure small infrastructure components (including power lines) before the advent of affordable UAV LiDAR systems, they can now carry out aerial inspections. Scanning power lines from the air allows surveyors to measure risk factors, such as the encroachment of vegetation.

LiDAR Power Cables with measurement GIF

Whether taking readings about the current status of power grid infrastructure or planning to build new power lines, utility providers can rely on 3D models from LiDAR drones. The fact that the vehicles fly means they can cross rough terrain more easily and safely.

Mining

Mining companies can measure ore extraction space with mines. By calculating surface data and comparing current to past readings, miners can determine their operations' progress. Drones provide a more economical option compared to airplane surveying , and are safer and more efficient than ground-based scanning.

Sending drones into mines is another valuable way to collect data while foregrounding safety. SLAM LiDAR can serve as a collision detection tool while also allowing the drone to map inside a mine. After a planned detonation, a drone can enter a shaft first, making sure the structure is sound enough for humans to enter.

Emesent Hovermap M300 1Matrice 300 RTK with an Emesent Hovermap

Archaeology

LiDAR drones are good at mapping the exact contours of structures — and these buildings don't have to be new. By using UAVs on an archaeological site, researchers can get a clear picture of the size and relative location of all relevant terrain features as well as any human-created remnants.

Mapping an archaeological site with a LiDAR UAV is quick and efficient compared to ground-based scanning and mapping methods. Since the drones can cover large areas, archaeologists can rediscover entire "lost" areas in a short time, even if those sites comprise entire ancient cities.

Stockpile volume measurements

Construction firms are going beyond surveying and using the systems for other functions such as inventory measurement. Repeatedly scanning a stockpile of materials allows a business to determine the rate of usage, allowing leaders to reorder at the right moment.

Understanding every aspect of a job site enables more efficient operations overall. Observing how much a stockpile changes in volume over time is possible with precise sensors, such as LiDAR, and mounting them on drones is an efficient way to put these solutions in action.