Mohamed M. R. Mostafa

Digital image georeferencing from a multiple camera system by GPS/INS

In this paper, the development and testing of an airborne fully digital multi-sensor system for digital mapping data acquisition is presented. The system acquires two streams of data, namely, navigation (georeferencing) data and imaging data. The navigation data are obtained by integrating an accurate strapdown inertial navigation system with a differential GPS system (DGPS). The imaging data are acquired by two low-cost digital cameras, configured in such a way so as to reduce their geometric limitations. The two cameras capture strips of overlapping nadir and oblique images. The GPS/INS-derived trajectory contains the full translational and rotational motion of the carrier aircraft. Thus, image exterior orientation information is extracted from the trajectory, during post-processing. This approach eliminates the need for ground control (GCP) when computing 3D positions of objects that appear in the field of view of the system imaging component. Two approaches for calibrating the system are presented, namely, terrestrial calibration and in-flight calibration. Test flights were conducted over the campus of The University of Calgary. Testing the system showed that best ground point positioning accuracy at 1:12,000 average image scale is 0.2 m (RMS) in easting and northing and 0.3 m (RMS) in height. Preliminary results indicate that major applications of such a system in the future are in the field of digital mapping, at scales of 1:5000 and smaller, and in the generation of digital elevation models for engineering applications.

Performance Analysis of Integrated Sensor Orientation

Integrated multi-sensor systems, with their major progress in terms of sensor resolution, data rate and operational flexibility, have become a very attractive mapping tool over the last decade. In aerial mapping application, for example, Exterior Orientation (EO) parameters for the imaging sensors are required. Using the integrated Differential Global Positioning System (DGPS) with Inertial Measurement Units (IMU), direct determination of the EO parameters can be obtained from the integrated system navigation solution. This process is referred to as Direct Georeferening (DG). DG provides substantial benefits over the indirect determination method of estimating the EO parameters from conventional Aerial Triangulation (AT) techniques using a block of images with a sufficient number of known control points. These benefits include the ability to map remote and inaccessible regions, and by replacing tie point measurements/matching and AT, significant cost-savings can be obtained for projects that do not require stereo models (such as projects with existing DEM or single image). The accuracy of DG, however, is limited by the accuracy attainable by the DGPS and any residual datum calibration errors. These can typically be as large as 10 cm RMSE, which is not sufficient for some large scale mapping applications. However, by combining the direct EO data a traditional block adjustment, AT techniques can be used to remove the residual errors in the solution. This technique is known as Integrated Sensor Orientation (ISO). It has several advantages over traditional AT, primarily because the stable geometry provided by direct EO can reduce the number of required GCP and tie-point to a minimum. At the same time, ISO provides an excellent tool for Quality Control/Quality Assurance (QC/QA) of the EO derived from a DG system. This paper examines the factors that determine the system performance for ISO. In addition, examples are given to illustrate the expected accuracy of an aerial mapping project using ISO under different qualities of DGPS/IMU data.

A Fully Integrated Solution for Aerial Surveys: Design, Development, and Performance Analysis

The focus of this paper is to present the current technological development in the field of system integration for data acquisition and georeferencing for aerial survey applications. The presentation is solely based on a commercial fully integrated system, the Digital Sensor System (DSS). The DSS is a fully-integrated, fully digital ruggedized system for airborne image acquisition, georeferencing, and map production. The DSS consists of a 4K X 4K digital camera, a GPS-aided INS direct georeferencing system, and a flight management system. The DSS software suite interfaces seamlessly with commercial off-the-shelf photogrammetric software allowing for fast topographic and orthophoto map production. The DSS currently uses a CCD chip with a 9 μm pixel size which allows digital image acquisition with a ground sample distance that ranges from 0.05 m to 1.0 m using its 35 mm and 55 mm lenses. The embedded POS AV direct georeferencing system provides the exterior orientation parameters in both real-time and post-mission modes. The DSS is used primarily to generate high-resolution color and color infrared digital orthophotos, orthomosaics, and topographic maps which can be used for many different mapping, GIS, and remote sensing applications.