The interference between two radar images, acquired from approximately the same location, has a number of uses. In particular, the literature abounds with examples of coherent change detection (CCD) and interferometric SAR (InSAR) uses which respectively enable the detection of small changes and the extraction of terrain elevation. In almost all of these examples collections have been deliberately constrained so that they have almost identical collection geometries. If the geometry of the collections differ then a severe degradation in the coherence or the products results when the images are formed in a conventional manner. This paper presents a new approach to image formation which simultaneously forms, focusses and interferes two images. This approach is not subject to the same geometry constraints and indeed works best when the ideal conditions are violated. As a byproduct of the process no image warping is required, the phase unwrapping problem and atmospheric phase grating effects can be eliminated.