What is meant by drone survey?

A drone survey refers to the use of a drone, or unmanned aerial vehicle (UAV), to capture aerial data with downward-facing sensors, such as RGB or multispectral cameras, and LIDAR payloads. During a drone survey with an RGB camera, the ground is photographed several times from different angles, and each image is tagged with coordinates.

Photogrammetry combines images that contain the same point on the ground from multiple vantage points to yield detailed 2D and 3D maps.

From this data, a photogrammetry software can create geo-referenced orthomosaics, elevation models or 3D models of the project area. These maps can also be used to extract information such as highly-accurate distances or volumetric measurements.

Unlike manned aircraft or satellite imagery, drones can fly at a much lower altitude, making the generation of high-resolution, high-accuracy data, much faster, less expensive and independent of atmospheric conditions such as cloud cover.

Drone Mapping Use Cases by Industry

Construction

The construction industry also greatly benefits from drone mapping. Maps can be used to regularly update clients in the construction industry on the progress of their projects, analyze stockpiles of raw materials such as dirt and gravel, or even generate 3D models of construction sites. These maps help construction managers obtain the “big picture” and assist in strategic decision making.

 

Mining

One industry that is already embracing mapping by drone is the mining industry. Up-to-date and detailed maps are used to manage stockpiles, water drainage, erosion detection, and pit and dump management among a host of other uses. Constantly updated maps can give managers better situational awareness that can assist in decision making.

 

Real Estate

Aerial maps are useful for aiding in the sale of land. For those considering buying large areas of real estate, an up-to-date aerial map can be of considerable value in determining if the property is right for them. If you have ever looked at a standard satellite image, you know that the detail is often lacking. Drone mapping can solve that clarity issue. A highly detailed aerial map allows for insight into the property details without requiring a client to be there in person. And with the help of a licensed land surveyor, contour lines and accurate borders can even be overlaid onto the imagery

 

Emergency Management

When disaster strikes, quick and accurate information is vital for emergency management to effectively respond, especially when the disaster covers a large area. Using drone photogrammetry, officials can determine the most damaged areas of a disaster (think flood or hurricane). With this data, they can effectively distribute their resources for a timely response. In 2017 we’ve seen drones at work in disaster relief during Hurricane Harvey, Hurricane Irma, and others, with drones being used in search and rescue work, and non-profit organizations.

 

Agriculture

The industry with the most potential for drone mapping is agriculture. Currently, agriculture is forecasted to be the largest use case overall for UAS. Maps give farmers the power to quickly analyze their crops and provide crucial data to guide decision making. Using NDVI imagery, a farmer with proper training can determine the health of his field and make important decisions in real time. Instead of walking the whole crop or traversing the field with a tractor, a drone can semi-autonomously produce a map and point out areas of trouble. This means that those in agriculture can save time, increase crop yield, and ultimately, improve their bottom line.

 

Land Surveying

Land surveyors are an obvious beneficiary of aerial mapping. Their job is to take precise measurements on pieces of land in order to determine boundaries. The data they collect assist in the creation of maps, plots, and legal documentation. With maps as a crucial part of their job, there is no doubt that drone photogrammetry can be helpful to their profession. Surveyors can obtain a highly accurate map with photogrammetry that can easily be turned into a 3D topographic map with contour data—a process that used to be extremely tedious. With their expertise and the possession of high quality equipment like RTK GPS units, surveyors can produce extremely accurate maps for their clients, and the efficiency drones provide helps them to expedite their workflow and improve their bottom line

 

Inspection

As you probably already know, inspection is becoming an important part of the UAS industry. Drone pilots primarily use cameras to visually inspect equipment, but photogrammetry can also assist in inspection. On a small scale, drones can help create a detailed map of a roof, and RGB and IR sensors can help to detect areas with leaks or poor insulation coverage. On a bigger scale, for example, the energy industry can use aerial maps to inspect solar farms, spotting problem spots in the solar panels with the aid of infrared imagery.

 

Forestry

Drone mapping can also be helpful to the forestry industry. With detailed maps, illegal logging can be detected and tracked, tree count can be determined, and the health of the forest can be monitored. Using NDVI imagery, areas of dry vegetation can be monitored, which can assist with forest fire prevention. Maps can also help identify dead trees, revealing whether a disease might be affecting the forest. The list goes on and on.

This resource was created to help you better understand how drones are being used in mapping and land surveying today, to provide some pointers about the mapping software out there, and to generally get you started if you’ve been considering adding mapping to your list of drone pilot skill sets.

Construction

The construction industry also greatly benefits from drone mapping. Maps can be used to regularly update clients in the construction industry on the progress of their projects, analyze stockpiles of raw materials such as dirt and gravel, or even generate 3D models of construction sites. These maps help construction managers obtain the “big picture” and assist in strategic decision making.

 

Key Mapping Terminology

• Photogrammetry—The science of taking measurements from photographs, usually those taken from the air.
• Orthomosaic—An aerial image corrected for topographic relief, camera tilt, and distortions in camera optic so that the scale of the image is uniform throughout.
• RGB Camera—This is the traditional type of camera used in mapping. It takes a sample of Red, Green, and Blue spectrums of light to create the image.
• NDVI—Also known as Normalized Difference Vegetation Index, which is a derived image (usually from a modified RGB or near IR sensor). NDVI takes the reflective light from the plant and ranks it on a scale from a -1 to +1 value. When there is a higher amount of reflective light from the plant, NDVI then correlates with a healthier plant, as the chlorophyll in the plant is what the light reflects off (plants that are not healthy have a lack of chlorophyll, and therefore reflect less light). NDVI is a valuable tool for those in agriculture and can be used to analyze crop health. Although NDVI is useful, it requires a certain degree of ground truth and proper analysis to be helpful to the end user. A standard NDVI map is typically not a helpful deliverable to the end user, but rather a tool for those who specialize in crop monitoring.
• GCP—Also know as a Ground Control Point, which is a physical marker on the ground that is used to keep your map geographically accurate. The location of a GCP is noted with an RTK (Real Time Kinematic) GPS (or other GNSS system) coordinate. This is a very accurate coordinate and allows your whole map to be aligned properly with the surrounding geographical area. Essentially, it makes sure that one point of the image is aligned with the precise GPS coordinate on the earth. This is very important if your map is going to be compared to an older map data, overlaid over other remote imagery, or relied upon for survey-accurate results.
• Near Infrared—A spectrum of light (electromagnetic radiation) that is slightly below the wavelength of visible light. NIR light reflected off a plant can be an indicator of how healthy it is. Special NIR, multispectral, or modified RGB cameras are needed to obtain this data.
• Infrared—IR is electromagnetic radiation or light with longer wavelength (lower frequency) than near infrared. The benefits of IR is that it can detect heat.
• Thermography—Thermography is imagery taken of the infrared spectrum of light. This imagery shows areas of heat in an object and is often used in industrial applications. The demand for thermographic work seems to be growing, and presents a new way for drone pilots to earn money.
• RTK—Also known as Real Time Kinematic satellite navigation, this is a centimeter-accurate technique of obtaining GPS (or any GNSS) data. Essentially, the RTK receiver analyzes the GPS radio signal to calculate this data. RTK is a big deal—an on board RTK receiver on a drone can negate the need for GCPs.
• Point Cloud—A point cloud is the collection of points or coordinates on an object’s surface. This collection of points can be used to create a 3D model of an area. Point Clouds are often derived from photogrammetric and LIDAR data.
• Relative Accuracy—In terms of mapping, relative accuracy refers to how accurate a point on a map is to other points on the same map. This means that if two points on a map are X cm apart on the map, they should be X cm apart in the real world.
• Absolute Accuracy—Absolute Accuracy refers to the accuracy of a point related to the coordinates in the real world. Absolute Accuracy means that a point on a map should match its actual GPS coordinates.
• Resolution—Resolution is the level of detail on a map. This is often measured in CM/Pixel, which means that for every pixel, X amount of CM will be represented on the map.

What are the benefits of drones in surveying?

Reduce field time and survey costs

Capturing topographic data with a drone is up to five times faster than with land-based methods and requires less manpower. With PPK geo-tagging, you also save time, as placing numerous GCPs is no longer necessary. You ultimately deliver your survey results faster and at a lower cost.

Provide accurate and exhaustive data

Total stations only measure individual points. One drone flight produces thousands of measurements, which can be represented in different formats (orthomosaic, point cloud, DTM, DSM, contour lines, etc). Each pixel of the produced map or point of the 3D model contains 3D geo-data.

Map otherwise inaccessible areas

An aerial mapping drone can take off and fly almost anywhere. You are no longer limited by unreachable areas, unsafe steep slopes or harsh terrain unsuitable for traditional measuring tools. You do not need to close down highways or train tracks. In fact, you can capture data during operation without an organizational overhead.

What are drones used for in surveying?

Land surveying / cartography

Survey drones generate high-resolution orthomosaics and detailed 3D models of areas where low-quality, outdated or even no data, are available. They thus enable high-accuracy cadastral maps to be produced quickly and easily, even in complex or difficult to access environments. Surveyors can also extract features from the images, such as signs, curbs, road markers, fire hydrants and drains.

After post-processing with a photogrammetry software, these same images can produce very detailed elevation models, contour lines and breaklines, as well as 3D reconstructions of land sites or buildings.

Land management and development

Aerial images taken by drones greatly accelerate and simplify topographic surveys for land management and planning. This holds true for site scouting, allotment planning and design, as well as final construction of roads, buildings and utilities.

These images also provide the foundation for detailed models of site topography for pre-construction engineering studies. The generated data can also be transferred to any CAD or BIM software so that engineers can immediately start working from a 3D model.

As data collection by drones is easily repeatable at low cost, images can be taken at regular intervals and overlaid on the original blueprints to assess whether the construction work is moving according to plan specifications.

Precise measurements

High resolution orthophotos enable surveyors to perform highly-accurate distance and surface measurements.

With 3D mapping software, it is also possible to obtain volumetric measurements from the very same images. This fast and inexpensive method of volume measurement is particularly useful to calculate stocks in mines and quarries for inventory or monitoring purposes.

With a drone, surveyors can capture many more topographic data points, hence more accurate volume measurements. They can also do this in a much safer way than if they had to manually capture the data by going up and down a stockpile. Since drones are capturing the data from above, operations on site won’t be interrupted. The short acquisition time enables capturing a site snapshot at a specific point in time.

Slope monitoring

With automated GIS analysis, it is possible to extract slope measurements from DTMs and DSMs generated by drone imagery. Knowing the steepness of the ground’s surface, the areas can be classified and used for slope monitoring purposes, including landslide mitigation and prevention.

With orthomosaics taken at different times, it is possible to detect changes in earth movement and to measure its velocity. This data can help predict landslides and prevent potential damage to roads, railways and bridges.

Urban planning

The development of increasingly dense and complex urban areas requires intensive planning and therefore time-consuming and expensive data collection. Thanks to drones, urban planners can collect large amounts of up-to-date data in a short period of time and with far less staff. The images produced in this way allow planners to examine the existing social and environmental conditions of the sites and consider the impact of different scenarios.

Thanks to 3D models, buildings can also be easily overlayed onto their environment, giving planners and citizens an experimental perspective of a complex development project. 3D models also allow analysis and visualization of cast shadows and outlooks/views.

What kinds of deliverables can you expect with drone surveying?

It depends on the camera or sensor and the software you are using for post-processing. RGB mapping cameras like the Sony’s RX1R II or QX1 together with most photogrammetry software can produce the following data:

Orthomosaic maps

Drone images are corrected for image distortion and stitched together during post-processing to create a highly-accurate orthomosaic map. Each pixel contains 2D geo-information (X, Y) and can directly procure accurate measurements, such as horizontal distances and surfaces.

File formats: geoTIFF (.tiff), .jpg, .png, Google tiles (.kml, .html)

3D point cloud

A densified point cloud can be generated from drone images. Each point contains geospatial (X, Y, Z) and color information. It provides a very accurate model for distance (slant and horizontal), area and volume measurements.

File formats: .las, .laz, .ply, .xyz

Digital surface models (DSM)

Drone images can also be used to create DSM models of the area. Each pixel contains 2D information (X, Y) and the altitude (Z value) of the highest point for this position.

File formats: GeoTiff (.tif), .xyz, .las, .laz

Digital terrain model (DTM)

After filtering objects such as buildings, the drone images can be used to create DTMs with each pixel containing 2.5D information (X, Y, and Z value of the highest altitude).

File formats: GeoTiff (.tif)

3D textured mesh

The 3D textured mesh is a reproduction of the edges, faces, vertices and texture of the area shot by the drone. This model is most useful for visual inspection or for when external stakeholders or public involvement is essential for a project.

File formats: .ply, .fbx, .dxf, .obj, .pdf

Contour lines

Depending on the project requirements, either the DTM or DSM model, with custom contour intervals, can be used to create a contour lines map, giving you a better understanding of the surface of the area shot by the drone.

File formats: .shp, .dxf, .pdf

How accurate is a drone survey?

The performance and type of drone, the quality of its components, the camera resolution, the height at which the drone flies, the vegetation, and the method and technology used to geolocate the aerial images can heavily influence the accuracy of drone survey mapping. At this point, it is possible to reach an absolute accuracy down to 1 cm (0.4 in) and 0.7 cm/px (0.3 in/px) GSD under optimal conditions with a high-end surveying drone such as the WingtraOne.

How to do a drone survey?

1. Check before you leave the office

Check the local regulations and make sure that you are allowed to fly your drone at the planned location. Also, make sure that the weather is suitable, meaning no rain, fog, snowfall or strong winds. Check that the battery of your drone and connected devices such as tablets are fully charged and that the memory card of your drone camera has sufficient empty space to capture the entire project.

2. Plan your flight

You can create the survey flight plan with the drone flight planning app on the tablet. For this, just tap and drag the points around the area you want to survey, or import a KML file. Make sure you account for tall objects within the flight plan, as well as altitude differences. If needed, you can adjust flight settings such as altitude, ground sampling distance (GSD), flight direction and images overlap.

3. Set up your flight in the field

During this step, you basically unpack and assemble the drone and make sure that it is ready to take-off in safe conditions. Following the interactive check-list, you will one-by-one check every parameter, like the calibration of the airspeed sensor and making sure the camera lid is removed.

4. Fly and collect images

After pushing the take-off button, the drone autonomously takes off, captures images and lands back where it started. In this step, the operator essentially makes sure that nobody approaches the drone during take-off or landing and that the weather conditions stay optimal for the survey mission.

5. Geotag your images

After one or several flights, import the images into WingtraHub software to geotag them s. Geo-tagging assigns geographical position (X, Y, Z) information to the images either in a separate CSV file or in the images’ meta-data.

How to process drone survey data?

While surveying with drones, images of the ground are taken from multiple vantage points. Through processing these images, a photogrammetry software can then create orthomosaics and 3D models, from which it can measure accurate distance, as well as surfaces and volumes of physical objects.

Data outputs from the drone

Images taken by the drone are usually saved on a memory card (such as SD card), just like for any other camera. Depending on the technology used by the drone, the images are already geo-tagged or can be imported in a geo-tagging software, such as WingtraHub. According to the size of the survey site, you probably have between a few hundred images and a few thousand, and each image contains geographical information (X, Y, Z).

Importing into a photogrammetry software

After importing or uploading the geo-tagged images in a photogrammetry software such as Drondeploy, delair.ai, 3DR Sitescan or Pix4D, images will be stitched together to create 2D or 3D models of the surveyed site. Image processing can be a lengthy process depending on the number of images and the performance of your computer. Some photogrammetry software are desktop-based, thus requiring robust hardware. Other software is cloud-based, employing powerful servers instead of your local computer to process the data.