How is Orthoimagery Made?
The first step in an orthoimagery project requires a thorough and accurate flight plan that takes into account project deliverables, historic weather conditions, and challenges such as flight-restricted areas, etc.
Based on the flight plan, flying altitude and sensor focal length, a grid of aerial imagery is acquired using a high-resolution digital aerial camera. As each image is acquired, an onboard Global Positioning System (GPS) measures the camera's exact longitude and latitude, while a ground GPS Base Station is measures from a known ground position relative to the constantly changing position of the aircraft.
An Inertial Measurement Unit (IMU) simultaneously measures the acceleration and rotational values of the aircraft (pitch / roll / heading). Data measured by both GPS and IMU are important for efficient imagery processing and higher accuracy, and can reduce the number of ground control survey points required for the mission / flight. In order to ensure that there are no gaps in coverage, each aerial image acquired allows for specified amounts of forward and side overlap.
Upon completion of the flight, GPS and IMU data are processed to generate the exterior orientation information for the acquired imagery.
The imagery, exterior orientation information, camera calibration, and ground control data all are ingested into a highly sophisticated Aerial Triangulation (AT) software package.
At every step in the ortho-mosaic process, the imagery, AT, DTM, orthorectification, and the resulting imagery mosaic product undergo rigorous quality control procedures to ensure that deliverables meet the project's required final accuracy and quality.
The orthorectified imagery is then seamlined together and color-balanced, creating a seamless, radiometrically uniform imagery mosaic for the entire project area.
Sample Flight Plan