Automatic image alignment for 3D environment modeling

We describe an approach for automatically registering color images with 3D laser scanned models. We use the chi-square statistic to compare color images to polygonal models texture mapped with acquired laser reflectance values. In complicated scenes we find that the chi-square test is not robust enough to permit an automatic global registration approach. Therefore, we introduce two techniques for obtaining initial pose estimates that correspond to a coarse alignment of the data. The first method is based on rigidly attaching a camera to a laser scanner and the second utilizes object tracking to decouple these imaging devices. The pose estimates serve as an initial guess for our optimization method, which maximizes the chi-square statistic over a local space of transformations in order to automatically determine the proper alignment.