3D building reconstruction from high-resolution Ikonos stereo imagery

An investigation of the application of 1m Ikonos satellite imagery to 3D building reconstruction is reported. The focus of the evaluation has been upon geopositioning accuracy, radiometric quality and attributes of the imagery that support building feature extraction. Following an initial review of characteristics of the Ikonos system, the multi-image dataset employed is described, along with the Melbourne Ikonos testfield. Radiometric and image preprocessing aspects are discussed and the results of 2D and 3D metric accuracy tests are presented. A quantitative and qualitative assessment of the use of stereo Ikonos imagery for generating building models is then provided, using the campus of the University of Melbourne as an evaluation site. The results of this assessment are summarised, these highlighting both the submetre metric accuracy potential of Ikonos imagery and difficulties to be anticipated in building reconstruction when a comprehensive and detailed modelling is required. sor and mission parameters, these are summarised in Table 1. Visitors to Space Imaging’s (SI’s) web site (www.spaceimaging.com) will note that there are basically five product options for panchromatic and pan-sharpened 1m Ikonos imagery: Geo, Reference, Pro, Precision and Precision Plus. Except for the Geo product, all are ortho-rectified, with ground control being required for Precision ortho-imagery. The absolute geopositioning accuracies (RMS, 1-sigma) associated with these categories of imagery are 24m, 12m, 5m, 2m and 1m, respectively. Table 1. Sensor and mission parameters for the Ikonos-2 satellite. ______________________________________________________________________ Focal length of steerable linear array 10 m Orbit altitude and period 680 km & 98 minutes Nominal image scale 1:68,000 Array length & pixel size 13,800 & 12 μm PAN Field of view 0.93 Footprint in panchromatic (nadir) 0.82m, resampled to 1m Footprint in multispectral (nadir) 3.3m, resampled to 4m Number of bits 11 Swath width at nadir 11 km Nominal scene size 11 x 11 km Revisit and repeat-cycle times 1-3 & 14 days (max) Stereo imaging: along-track, with cross-track possible ________________________________________________________ Depending on the intended function of a digital city model, metric accuracy expectations will vary, though if the very sizeable market of modelling for mobile communications is to be accommodated, accuracies at the metre level are generally sought. The clear implication from the product offerings listed above, however, is that users of Ikonos imagery who seek metre-level accuracy will have to resort to acquisition of expensive Precision imagery. We have pursued an alternative option, with the aim of yielding high accuracy results, to metre or sub-metre level, using the least expensive Ikonos data, namely Geo images, coupled with alternative computational schemes for mono-, stereoand multi-image positioning. A few accounts of Geo imagery being employed for ortho-image production to metre-level accuracies have been recently published (e.g. Kersten et al. 2000, Gruen 2001, Davis & Wang 2001), though the only results to date that the authors are aware of involving 3D geopositioning from stereo triangulation have emanated from SI (Dial 2000). The reported stereo results were, perhaps not surprisingly, both encouraging and consistent with Ikonos product specifications. One can imagine a number of disincentives for SI to promote the use of Geo imagery for higher accuracy applications.