As imagery is collected from an airborne platform, an individual viewing the images wants to know from where on the Earth the images were collected. To do this, some information about the camera needs to be known, such as its position and orientation relative to the Earth. This can be provided by common inertial navigation systems (INS). Once the location of the camera is known, it is useful to project an image onto some representation of the Earth. Due to the non-smooth terrain of the Earth (mountains, valleys, etc.), this projection is highly non-linear. Thus, to ensure accurate projection, one needs to project onto a digital elevation map (DEM). This allows one to view the images overlaid onto a representation of the Earth.
A code has been developed that takes an image, a model of the camera used to acquire that image, the pose of the camera during acquisition (as provided by an INS), and a DEM, and outputs an image that has been geo-rectified. The world coordinate of the bounds of the image are provided for viewing purposes. The code finds a mapping from points on the ground (DEM) to pixels in the image. By performing this process for all points on the ground, one can “paint” the ground with the image, effectively performing a projection of the image onto the ground. In order to make this process efficient, a method was developed for finding a region of interest (ROI) on the ground to where the image will project.
This code is useful in any scenario involving an aerial imaging platform that moves and rotates over time. Many other applications are possible in processing aerial and satellite imagery.
This work was done by Adnan I. Ansar, Shane Brennan, Daniel S. Clouse, Yang Cheng, Curtis W. Padgett, and David C. Trotz of Caltech for NASA’s Jet Propulsion Laboratory.
The software used in this innovation is available for commercial licensing. Please contact Daniel Broderick of the California Institute of Technology at
This Brief includes a Technical Support Package (TSP).
Projection of Stabilized Aerial Imagery Onto Digital Elevation Maps for Geo-Rectified and Jitter-Free Viewing
(reference NPO-46920) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, focusing on the projection of stabilized aerial imagery onto digital elevation maps (DEMs) for geo-rectified and jitter-free viewing. It addresses the challenges associated with aerial surveillance, particularly the difficulties in accurately geo-rectifying images collected from Unmanned Aerial Vehicles (UAVs) due to factors like aircraft motion, 3D terrain relief, and the dynamic nature of moving objects.
Geo-rectification is essential for relating pixel coordinates in aerial images to their corresponding real-world locations (latitude and longitude). The document emphasizes that this process is complicated by perspective changes and the limitations of existing DEMs, which may be outdated and have low resolution compared to the high-resolution imagery captured by aerial platforms.
One significant issue highlighted is the phenomenon of "jitter," which refers to the instability in imagery that should appear steady. Jitter can occur due to various factors, including inaccuracies in the inertial navigation systems and camera models. The document explains that while poor camera models are less problematic, the inaccuracies in the Earth model and navigation systems can lead to significant visual disturbances in the imagery.
To combat jitter, the document introduces an image stabilization algorithm developed by the authors. This algorithm aims to identify and correct the movement between two images, effectively warping one image to align with the other. The result is a set of images that are not only stabilized but also tagged with metadata, allowing for accurate overlay with other data collected for the same geographic area.
The document also mentions that the output of the image stabilization process can be demonstrated through a video encoded with the “Microsoft Video 1” codec, which showcases the effectiveness of the algorithm. The overall goal of the research is to enhance the quality and usability of aerial imagery for various applications, including military operations, law enforcement, and rescue missions.
In summary, this Technical Support Package outlines the importance of geo-rectification and image stabilization in aerial surveillance, presenting innovative solutions to improve the accuracy and clarity of aerial imagery for practical applications.
