The introduction of low-cost commercial UAV technology has been helping us conduct operations that are dangerous, time-consuming, or uneconomical to be carried out by manual methods. They have numerous advantages over piloted aircraft, including lower image acquisition costs, the ability to fly at low altitude and low speeds, and with higher accuracy.
Commercial GIS software like DroneDeploy, Pix4d, Indshine etc. can be used to visualize these 3D models and calculate the volume of an area of interest. Volume estimations can be done from generated surface models created by a highly accurate ground-based Light Detection and Ranging (LiDAR) sensor. Volumetric Estimation is done in cases where accurate measurement is either time consuming, not manually feasible, or extraordinarily complex.
Traditional Volumetric Estimation Techniques
Manual volumetric estimation is a tedious process which consists of performing a detailed manual survey. The surveyor has to capture coordinates, conduct elevation profiling, and generate a 3D surface model, and then do the volumetric calculations and comparisons for each stockpile. This extremely tedious process has significant accuracy limitations.
Use cases of UAV Volumetric Estimation
- Disaster management
An important use case is for disaster relief and management. The first responders have to estimate the amount of material needed to rebuild and repair the damaged infrastructure. Currently, this includes a human survey with ancient equipment which is expensive, time-consuming, and inaccurate. Drones can be used to obtain stereo imagery which can be useful in estimating volumes.
In the construction industry, there is a need for constant monitoring of stockpile volumes to make sure that there is enough material for construction at all times while ensuring no wasteful overstocking. It is also essential to plan the financial report of inventory. In such cases, accurate measurement is required which can be easily achieved by drones.
Mining needs regular Volumetric estimation periodically to monitor the progress and regulate mining workflow.
- Detection of Illegal Mining activities
Drones can be used to identify the violations in terms of area, depth, and volume. High spatial resolution images are obtained quickly at less costs and human errors.
- Terrain analysis
The measurement and documenting of limestone quarries, cliff faces, and natural formations is now done using drones. They photograph the area and the pictures are later converted into 3D terrain models for analysis.
- Groundwater estimation
Groundwater levels and depth to water data are needed for researchers working in such ecosystems. The groundwater mapping is done using orthophotography and photogrammetric point clouds that are generated from images acquired by drones.
How is the Volumetric Estimation done?
The process is done by performing elevation profiling by drones using photogrammetry techniques or LiDAR technology.
In photogrammetry, a series of high-resolution images are captured by cameras and then used to generate 2D or 3D models using Optics and projective geometry principles.
In LiDAR a point cloud is generated by accurately computing the position of each point based on the reflection of laser beams transmitted by LiDAR sensors. A 3D model is generated using the point cloud. LiDAR is more accurate, reliable, and expensive than photogrammetry.
- Preflight Visual Inspection of perimeter
A preflight check of the perimeter is done to take note of any potential obstacles that might impact the volume calculations. These will be used to accurately annotate perimeter points.
- Aerial Mapping
Geotagged aerial images are captured using photogrammetric or LiDAR techniques. The acquired data is further processed to generate a map.
- Generating a 3D model and Digital Elevation Map
3D models and DEMs are generated using powerful tools and photogrammetric techniques or point cloud data obtained from LiDAR systems.
- Volume Calculation
Perimeter points are carefully selected to avoid errors. It is recommended to use the elevation layer to define perimeters as sometimes small piles can be overlooked or nearly invisible in the case of orthomosaic maps due to homogenous coloring and shadows. Therefore we recommend the use of the elevation layer as the base layer of the map.
The software will automatically compute the volumes of the stockpile or object using its digital elevation model and mathematical equations.