The RADIUS Common Development Environment pulls together many diverse functions into an integrated whole. The main goal of the environment is to provide a system to do interactive modeling of 3-dimensional scenes from multiple images, as well as, providing an infrastructure to support the research in and implementation of image understanding-based algorithms for this and other tasks. The RCDE contains facilities for: CAD-system-like 3D modeling; image processing; electronic-light-table image viewing and exploitation; frame and non-frame camera photogrammetry; and photo realistic rendering. The major achievement of the system is the high level of integration and interoperability between and among these facilities. The key realization that enables this is that every entity represented in the RCDE has an associated local coordinate system. This includes cartographic and cultural features, images and sub-images, text annotations, graphical user interface elements, photogrammetric conjugate points and even the earth itself. These entities are tied together through a flexible and efficient network of coordinate transformations. This allows each type of data to be represented, manipulated, and displayed in the most convenient and precise form, without sacrificing functionality or generality, in addition to enabling the fusion of different types of geometric data. In this paper, we explain the coordinate system representations and transformation facilities in the RCDE and outline some of the rationale and strategies behind the current design and implementation. Also included are examples drawn from its use in the government sponsored RADIUS program.