ABSTRACT
The alignment of images with a digital elevation model (DEM) has many applications in the planetary mapping field. In this chapter, we propose a novel highly precise co-registration method that can achieve direct pixel-based matching between an image and a reference DEM. The DEM is first converted into a simulated image using a hill-shading technique based upon a photometric model and the image’s illumination conditions. Initial matching between the simulated image and the input image is then performed based on affine scale-invariant feature transform (ASIFT). Meanwhile, the image’s rational function model is established and used as a geometric constraint. Next, the tie points generated by the initial ASIFT matching are used to refine the rational function model geometric model of the image and to eliminate the gross errors of tie points in an iterative fashion. Finally, highly precise co-registration is performed by pixel-based least-squares image matching using the refined geometric model as a global geometric constraint. Two Lunar Reconnaissance Orbiter (LRO) narrow-angle camera images located at the pre-selected landing site of the Chang’E-5 mission and the SLDEM2015, a combined product of lunar orbiter laser altimetry (LOLA) and DEM generated from the Japanese Selenological and Engineering Explorer (SELENE) terrain camera images, were selected in our experiment. The results demonstrate that the proposed method can achieve effective pixel-based matching between an image and a reference DEM with a mean accuracy of 15.6 pixels in the image space and 20.95 m (0.5 pixel of the reference DEM) in the object space. Another 15 narrow-angle camera images that were evenly distributed at various latitudes were selected as an additional experiment to evaluate the matching precision of various DEM densities. The results show that the precision improved in a near-linear manner as the latitude increased. Thus, the denser the DEM, the greater the matching precision. The proposed method offers a highly precise and automatic method of matching orbiter images with DEMs.
