Global 3D Terrain Maps for Agricultural Applications

摘要

At some point in life, everyone needs to use a map. Maps tell us where we are, what is around us, and what route needs to be taken to reach a desired location. Until very recently, maps were printed in paper and provided a two-dimensional representation of reality. However, most of the maps consulted at present are in electronic format with useful features for customizing trips or recalculating routes. Yet, they are still two-dimensional representations, although sometimes enriched with real photographs. A further stage in mapping techniques will be, therefore, the addition of the third dimension that provides a sense of depth and volume. While this excess of information may seem somewhat capricious for people, it may be critical for autonomous vehicles and mobile robots. Intelligent agents demand high levels of perception and thus greatly profit from three-dimensional vision. The widespread availability of global positioning information in the last decade has induced the development of multiple applications within the framework of precision agriculture. The main idea beyond this concept is to supply the right amount of input at the appropriate time for precise field locations, which obviously require the knowledge of field coordinates for site-specific applications. The practical implementation of precision farming is, consequently, tied to geographical references. However, prescription and information maps are typically displayed in two dimensions and generated with the level of resolution normally achieved with satellite-based imagery. The generation of global three-dimensional (3D) terrain maps offers all the advantages of global localization with the extra benefits of highresolution local perception enriched with three dimensions plus color information acquired in real time. Different kinds of three-dimensional maps have been reported according to the specific needs of each application developed, as the singular nature of every situation determines the basic characteristics of its corresponding 3D map. Planetary exploration, for example, benefits from virtual representations of unstructured and unknown environments that help scouting rovers to navigate (Olson et al., 2003; Wang et al., 2009); and the military forces, the other large group of users of 3D maps for recreating off-road terrains (Schultz et al., 1999), rely on stereo-based three-dimensional reconstructions of the world for a multiplicity of purposes. From the agricultural point of view, several attempts have been made to apply the mapping qualities of compact binocular cameras to production fields. Preceding the advent of compact cameras with real-time capabilities, something that took place at the turn of this century, airborne laser rangefinders allowed the monitoring of soil loss from gully erosion