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.

In this blog series, we will embark on a captivating journey through the realm of photogrammetry and its outputs.

Photogrammetry is a technique used to measure and map physical objects or environments using photographs. It combines the principles of photography and geometry to create accurate 3D models or measurements from 2D images. Photogrammetry is used in the military, construction, land surveying, real estate, etc.

Through the process of photogrammetry, multiple images of an object or scene are captured from different angles or viewpoints. These images are then analyzed and matched to extract precise measurements, shapes, textures, and even colors. The software algorithms used in photogrammetry can reconstruct the 3D structure of the object based on the visual information provided by the images.

With the help of a Worldfile we can also import an orthomosaic into AUTOCAD and georeference it with the help of the GEOREFIMG AutoCAD command.

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

• JPEG: JPEG is a common image format and orthomosaic maps can be saved as high-quality JPEG files. While they are more accessible for visualization, they may lack the georeferencing information that GeoTIFF provides.

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

I have used Surveyaan Geoworkspace photogrammetry software to create the orthomosaic and its formats.

The possibilities of orthomosaic mapping are limitless, and as technology continues to advance, we can expect even greater achievements and innovations.

An IMU with strong vibration resistance and good performance will enhance drone flight performance.

Accelerometer also gives linear acceleration in the horizontal and vertical directions. This data can be used to calculate the velocity, movement, and even rate of change of altitude of the drone.

Sensors that measure air pressure are called Barometers. Drones use this air pressure data to calculate their altitude.

The Government released several sets of instructions to allow the operation of UAV drones called the Standard Operating Procedures (SOP) for carrying out drone survey and submission of Digital Aerial Images of Mining areas to Indian Bureau of Mines.

Standard Operating Procedures for carrying out drone survey and submission of Digital Aerial Images of Mining areas to Indian Bureau of Mines

From Airspace Map of India above, In the Airport Yellow [8-12 km] zone , drones can be operated only upto 60m. In the Airport Yellow [5-8 km] zone and Airport Red zone , drones can be operated only after permission from DGCA.

From the figure as shown above, we can see that this is the International Boundary. This is a highly restricted zone.

8. Co-ordinate Reference System

From the Figure above, these are the photos captured by the drone and here you can see that the (Latitude, Longitude) values are in Degree Minute Second (DMS).

The Orthomosaic shall be submitted in the Universal Transverse Mercator (UTM) and unit as meters.

From Figure  above, this is an orthomosaic file and here it is in UTM Coordinate Reference System having EPSG Code: 32643 and the coordinate values are in meters.

The GCPs survey data and boundary pillar coordinates shall be submitted in (Latitude, Longitude) with WGS84 Datum and Degree Minute Seconds as unit.

The precision of the data submitted in (Latitude, Longitude) with WGS84 Datum should be in format as (DD MM SS.SSSSSS)

From Figure  above, it shows the properties of an image used in drone survey. Here the (Latitude, Longitude) values are in Degree Minute Second (DMS) and in the seconds value you need to have precision upto 6 digits.

9. Preservation of Raw and Processed Data

The raw and processed data of each survey must be kept safely with the lessee for a minimum period of five years. The data must be submitted to IBM in case required by IBM for verification at any stage. The data can be stored in cloud platforms such as Surveyaan Geoworkspace, so that there is no risk of getting the data lost or corrupted.

Now, we will continue in the next blog mentioning about the data outputs and formats needed to be submitted to IBM.

Mining is the extraction of valuable minerals or other geological materials from the earth. The profitable substances that are mined from the earth are called minerals. The minerals are valuable in their pure form, but in earth they are mixed with unwanted rocks and minerals. This mix of mineral and rock is usually carried away from the mine and processed later and refined to isolate the mineral

The Indian Bureau of Mines (IBM) established in 1948, is a multi-disciplinary government organization under the Department of Mines. It is headquartered at Nagpur, Maharashtra. It is engaged in promotion of conservation, scientific development of mineral resources and protection of environment in mines other than coal, atomic minerals, petroleum & natural gas and minor minerals. It is primarily advisory body to help in formulation of policy and legal framework for mining sector and advising Central and State Governments on development and utilization of mineral resources.

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.

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.

Drones have transformed the way we capture information. They collect massive amounts of high-quality data in real-time. Three types of missions are generally used in Drone surveys to aid the process of data collection. The user can choose a mission depending on his/her project’s requirements. Once the mission is selected, the drone flies to the initial point and takes photos regularly until it reaches the endpoint. The captured images are then processed in any photogrammetry software to obtain the results.

Drones are a potent tool for government agencies, research scholars, and businesses. Even though modern UAVs use sophisticated technologies to reduce accidents, you should always fly cautiously. Let’s take a closer look at how to safely operate these machines in different terrains.

Volumetric measurements are done using aerial or ground surveying techniques to calculate the volume of stockpiles and other materials. Conventionally, it was done on the ground using total station but now, as an alternative, aerial UAVs are used to find the measurements. Surveyors now use drones to calculate the stockpile volume and amount of material removed from the ground. They plan accurate projects at different timeframes, and measure excavations. Surveys are done on the mine, quarry, landfills, coal yards, etc.

Before moving on to the Volumetric calculation, you have to be familiar with some terms given below.

Linear fit: Concerning the points in the polygon, a linear fitted plane will be considered, and the plane that fits the best will be used for calculating the volume. The linear fit is used to calculate the volume of stockpiles whenever the ground underneath the stockpiles is sloped or irregular.

Here in Figure 8 above, you can see two project photos. The photo on the left is the area surveyed first and to the right is a photo of the same area surveyed after one month.