The use of Unmanned Aerial Vehicles (UAV) imagery for GIS data acquisition is constantly evolving. The ease of use, agility of the flying machines, quick turnaround time for generating accurate data, and low data acquisition costs have made UAV’s very popular with end customers and data acquisition companies. This article highlights UAV data processing steps and discusses areas of applications.
Processing UAV Imagery
The accuracy of aerial data is directly related to the spatial resolution of the input imagery. The high resolution images from UAV can compete with traditional aerial mapping solutions that bank on highly accurate alignment and positioning sensors on board. The advancement of computing practices resulted in vigorous and fully automatic production practices and coupled with high-end computing machines and viewing mechanisms will deal with positional inaccuracies and imagery orientation information which are characteristically challenging with customary techniques.
SBL’s geospatial team processes such images. Processing of UAV images has its own challenges. SBL used to receive post-processed UAV images along with inertial measurement unit (IMU) and ground control points (GCP) as input. Aerial Triangulation is the first step performed. During this stage GCP and Actual Check Point (ACP) reports have been generated. This is an iterative step until we get the desired accuracy. The following will explain in brief some of the critical steps in the processing of UAV data.
- The software examines for matching points by analyzing all images. The software used here an improved version of the binary descriptors, which are very powerful to match image points quickly and accurately.
- Those matching points as well as estimated values of the image position and orientation provided by the UAV autopilot are used in a bundle block adjustment to reconstruct the exact position and orientation of the camera for every acquired image.
- Based on this restitution the matching points are corroborated and their 3D coordinates calculated. A proper projection system is selected based on the requirements, and also GPS measurements from the UAV autopilot during the flight.
- 3D points are interpolated to form a Triangulated Irregular Network (TIN) in order to obtain a DEM. The spatial resolution of the TIN is moderated as per the need of 3D model requirements.
- This DEM is used to project every image pixel and to calculate the geo-referenced ortho-mosaic. The orthoimages will be cleared of positional and terrain displacement inaccuracies.
Applications of UAV Imagery
One of the major application for which UAV images used is for agriculture. UAV images are ideal for small sized farms. Plant counts such as corn counting will give an idea of yield from those plants. Plant health monitoring, differentiating species of agricultural farms/plants and plantation estimation are the major task performed for agriculture. Growth stages of the farms can also be monitored using ortho images acquired through UAV process. UAV image processing is also helpful for the site selection for solar farms.
In case of forestry, UAV images are very helpful in species identification. SBL’s interpreters have identified forest species and enabled the client to map forest land parcels. It is a tool to monitor de-forestation as well as afforestation. Golf courses are another field where UAV data sets are highly useful. Golf course features can be mapped with their actual heights through this process.
Mining industry is the most benefitted in the usage of UAV technological advancement. As most of the mines are spread over small areas, UAV data acquiring and processing is very cost effective. Along with other data processing, SBL has got the expertise in generating contours and mining related features to very minute levels of detail.
About the Author
Anil Narendran Pillai – (Vice President – Geomatics @ SBL)
Mr. Pillai heads the GSS (Geospatial Services) domain at SBL (www.sblcorp.com). He has worked in the digital mapping, remote sensing, and GIS industries for over 23 years. He has 23+ years experience managing and coordinating GIS projects and 12 years senior management experience. He has extensive experience in all aspects of aerial and satellite imaging technology and applications. He has utilized remotely sensed satellite and airborne imagery for a variety of environmental applications including site location analysis, forestry, telecommunications and utility corridor mapping. He has a strong background in management of GIS and Photogrammetry imaging projects to support Government and private industry needs.His Passion lies in Need Analysis and Documentation, Topographical Mapping (ArcGIS), Spatial Data Management, Integrity and Security, GIS Data transformations and projections from multiple sources, Image Processing Software user testing and documentation, Project Coordination and Tech. Support, Inter-agency communication and support, 3D Data Generation and Management, Project Management, Digital Photogrammetry, Satellite Image Processing, Pre-Sales Presentations.