Applications

Surveying and Mapping

• In the world of surveying and mapping, accuracy is indispensable for creating reliable and detailed spatial representations.
• Accurate land surveying is essential for a variety of purposes, such as determining property boundaries, creating topographic maps, and supporting the construction of buildings and infrastructure.

Since now we know why accuracy is a very important factor in our daily commutes, let us take a journey into the world of GNSS.

While Global Navigation Satellite Systems (GNSS), such as GPS, provide widespread and reliable positioning information, the limitation of the standalone GNSS is in its accuracy.

The above illustration shows how the other photogrammerty outputs are generated using point cloud

Point clouds significantly enhance the capabilities of drone surveying by providing accurate, detailed, and comprehensive spatial data. This integration of technology is instrumental in improving decision-making, reducing risks, and increasing the efficiency of various applications across industries, ultimately contributing to better-informed and more sustainable practices.

The Digital Terrain Model is a subset of DEM and consists of the earth’s surface and excludes buildings, trees, etc

The Digital Surface Model is a subset of DEM and consists of the earth’s surface, including all objects like buildings, trees, etc.

This illustration gives you a more detailed view and understanding on the Digital Surface model and the digital terrain model. The black line is represented by the digital surface model and as you can see here it has taken the elevation of the trees, house and the poles. The red line is represented by the digital terrain model and it has excluded the elevation of the trees, house and poles.

• GeoTIFF (Georeferenced Tagged Image File Format):It combines image data with geospatial information, allowing it to be precisely located on the Earth’s surface. This format is compatible with various Geographic Information System (GIS) software and is suitable for many geospatial applications.

• Worldfile: It is a six line plain text sidecar file used by geographic information systems (GIS) to georeference raster map images.
  

• Slope: It identifies the steepness. The lower the slope value, the flatter the terrain; the higher the slope value, the steeper the terrain.
  

• PDF (Portable Document Format): DEM’s can be exported as PDFs for easy sharing and printing. However, like JPEG, they may not contain geospatial data.
  

• CSV File: Comma-separated files contain latitude, longitude and elevation information in a text file, with each data category (or “column”) separated by a comma.
  

To sum up, digital elevation models are essential resources for drone surveys. They enable experts in a range of disciplines to reduce risks, streamline procedures, and make well-informed judgements. The combination of drone technology and the growing availability of different kinds of digital elevation models (DEMs) has the potential to completely transform how humans interact with our surroundings and manage our resources. Drones and DEMs can help you shape a better, more sustainable future whether you’re a land developer, environmentalist, urban planner, or geospatial scientist.

A Geographic Coordinate System (GCS) is a reference framework that defines the locations of features on an earth model. These coordinates are based on an ellipsoid that approximates the Earth’s shape, allowing us to measure distances and angles between different points of the Earth. In Geographic Coordinate System, locations are defined using angular measurements, usually in decimal degrees. A GCS is required for the data to pinpoint its location on the earth’s surface accurately. The most commonly used geographic coordinate system is the World Geodetic System 1984 (WGS 84).

To represent a location in GCS, you need the location in either degree minute seconds or decimal degrees. This is an example of GCS.

Let us find out the location of the Bangalore Cantonment Railway Station. Consider the location of the railway station to be 12°59'37.38"N and 77°35'52.87"E in Geographical Coordinate System. Here the location is in Degree Minute Second format.

From the figure above, we can see horizontal lines run east — west. They are called Latitudes or Parallels. They form concentric circles around the Earth and are equally spaced and parallel to one another. The Equator is the line of latitude that cuts across the center of the Earth and marks zero degrees of latitude. Positive latitudes from 0 to +90 degrees are found north of the equator, while negative latitudes from 0 to -90 degrees are located south of the equator.

From the figure above, we can see vertical lines run north — south. They are called Longitudes or Meridians. The Prime Meridian is the line of longitude that is at zero degrees and runs from the North Pole to the South Pole. For most geographic coordinate systems, the prime meridian is the longitude that passes through Greenwich, England. Positive longitudes from 0 to +90 degrees are found east of the Prime Meridian, while negative longitudes from 0 to -90 degrees are located west of the Prime Meridian.

From the figure above, the grid-like network of latitude and longitude lines encircles the entire globe and is called the Graticule. The equator and prime meridian intersection define the origin of the graticule (0,0).

A spheroid or a sphere approximating the Earth’s shape can define a coordinate system. A sphere is based on a circle, whereas a spheroid is an ellipsoid based on an ellipse.

There are many different models of the earth’s surface and, therefore, many different GCS. World Geodetic System 1984 (WGS 1984) is designed as a one-size-fits-all GCS, good for mapping global data. Australian Geodetic Datum 1984 is designed to fit the earth snugly around Australia, giving you good precision for this continent but poor accuracy anywhere else.

The Ministry of Civil Aviation launched an airspace map of India for drone operations on 24 September 2021 for the first time. It enables civilian drone operators to check for delineated no-fly zones or areas where certain formalities must be completed before flying a drone. The map is available on the Directorate General of Civil Aviation’s (DGCA) digital sky platform.

The drone airspace map is an interactive map of India that demarcates the country’s red, yellow, and green zones. Anyone planning to operate a drone should mandatorily check the latest airspace map for any changes in zone boundaries from the digital sky website.

Green zones are unrestricted zones where drones can be operated without any permission. The green zone is the airspace up to 120 m/400ft that has not been identified as a red or yellow zone. Permission is unnecessary to operate drones weighing up to 500 kg in green zones.

Yellow zones are controlled zones, and the drone can only be operated after permission from DGCA. The yellow zone is the airspace up to 120m/400ft in a designated green zone, up to 60m/200ft in the vicinity of an operating airport that is between 8 and 12 kilometers away, and above ground in the vicinity of an operational airport that is between 5–8 kilometers away.

From Figure 2 above, In the Airport Yellow [8–12 km] zone, drones can be operated only up to 60m/200ft. You need to take permission from the authorities in order to fly above this height.

There are international boundaries besides the Green, Yellow, Red, and Geo Zones. This is a highly restricted zone. You are not allowed to fly the drone here

Remote Pilot License

In India, Drone Pilot Training is now mandatory to fly a commercial-purpose drone of any size. To become a professional drone pilot in India, candidates must obtain a drone pilot license upon completing training from a DGCA (Directorate General of Civil Aviation) approved institute. Flying a drone without the required certificate can result in severe fines and drone confiscation.

To be eligible for the program, One must be at least 18 years old and under 65. They should also have a minimum qualification of Class 10. Candidates must also pass a medical examination and a background check from the relevant government agency. It is not necessary to own a drone to enlist.

This brings us to the end of the blog. I hope this article gained some knowledge for you!

Thank you for reading.

KML Creation: Create a KML of the site you want to map. Make the site’s boundary large enough, so you don’t miss any area you plan to map. With the help of earth browsers such as Google Earth, you can study the area you want to map by inspecting the area. Make sure to confirm that no structures such as chimneys, tall trees, buildings, or any other construction hinders the drone’s path. If any construction or facility that may threaten the drone is inside the boundary of your site, plan in a way that you fly above it.

Splitting the KML: If the area is large enough and has varied landscapes on your site, you need to break the KML. Split the KML according to your requirement and give a unique identification to the KMLs created. While splitting the KML, make sure to have overlapping between adjacent KMLS. Also, you can find a safe and clear elevated area as your home position (Drone Take-Off Position). Make sure the home position is accessible by road and is open and clear. Save the location of the home position while planning.

E.g., From Figure above, we can see that this is a mining terrain with a boundary of 310 hectares. The maximum elevation on the left part of the site is 365m, and the maximum elevation on the right part is 480m.

We need to split the KML into two parts since there is an elevation difference of more than 110m. We have saved the KML to Boundary A and Boundary B. Boundary A and B have areas of 144 and 166 hectares, respectively. 30m Overlapping is ensured between the adjacent KMLs denoted by the red line. The home position is represented by the yellow pinpoints and is saved as Home 1 and Home 2, respectively. The home position of Boundary A can be set at any safe and clear point whose elevation is above 345m. The home position for Boundary B can be selected at any safe point whose elevation is above 460m. Here the home positions are set at 354m and 465m, respectively.

While marking the home position, ensure the boundary is within the drone range. The drone range varies with different drones. We can find the distance from the home position using the Measure Distance and Area option from Google Earth. Measure and check if the boundary exceeds the drone range. Change the home position if the boundary exceeds the drone range.

GCPs can also be placed in each KML. Generally, per sq. km or 100 Hectares, 4–5 GCPs are more than sufficient to geo-reference raster data. The thumb rule of placing the GCP is that wherever there’s an abrupt change in the terrain, you can set the GCP, and also, GCPs should be spread out uniformly throughout the landscape. Since the boundary A and B have an area of more than 100 hectares, we can place 6 GCPs per KML.

Setting the Overlap: Each drone has a different field of view (F.O.V.) based on the camera. This has consequences for mission planning, particularly for mapping missions that cover large areas. Overlap matches the features between photographs. There are two types of overlap:

Increasing the overlap for a flight creates more matched points and greater accuracy. Lower altitude and higher overlapping will increase the number of images and the time required for the flight, but worth it in the long run, as this helps obtain high-resolution images.

Altitude and GSD: It may also come as no shock that flying the drone at a higher altitude helps the camera cover more land area in a single image with fewer batteries and less time overall. This interprets more enormous possibilities for capturing distinctive features in multiple images. But the reciprocation is that the image’s resolution and accuracy will be compromised. Flying at low altitudes captures more details of the area. It also helps match common points while processing, increasing the image resolution and accuracy.

GSD is the distance between the centers of two successive pixels on your map, measured in inches, centimeters, or millimeters. A drone can measure with a GSD of 5 cm/px, meaning that each pixel on your digital map represents 5 centimeters of actual space in the real world.

Battery: The optimization of your battery life will differ depending on the type of drone you use. Mapping large areas require more than one battery to map the whole area. Make sure to carry extra batteries and plan efficiently to save battery life. If the site is large, then you need to make battery swaps. The drone returns home when the battery gets low, and you need to swap the battery and resume the mission. The drone then flies to the position from which it triggers a return home and continues the mission. Store your batteries in a place with stable temperatures.

Environmental factors: Plan and keep an extra day mapping large areas due to environmental factors such as precipitation, wind, etc. It is wise to avoid flying your drone at high wind speeds. You can estimate the wind using wind apps. My personal favorite is windfinder.com. This app has detailed wind forecasts and weather forecasts that let you always find the spot with the best wind weather conditions. Every drone pilot needs to have this app because it will help you plan your flight well.

Check Data in the Field: Technical errors, like camera glitches, overexposed photos, etc., may arise while you are on the field. It is always recommended to review the data you have collected while you are still on-site to make any necessary corrections. The Map Viewer tool from this website solved my problem of checking data in the field. This free tool allows you to upload images, GCP, and KML. The user can then verify that all the images taken are within the KML border by viewing the photos and flight path on a base map.