Localization of Visually Indistinguishable Mature Lettuce Heads Using Spatial Information

This paper describes an approach to recognizing and localizing centers of mature lettuce heads in the field when the lettuce leaves obscure the distinctions between plants. This is of great value when using an automatic harvester in cluttered or closely planted vegetation. The aim of this work is to investigate and verify the potential use of spatial rather than visual clues for recognition and localization, with a view to implementing a more robust and sophisticated system if promise is shown. Colour/texture information was difficult to use so spatial information was used instead. A laser range finder was used to generate a height plot from above the plants. Lettuce examples were used to learn the radial distribution of the lettuce model. This was compared with the distributions of arbitrary locations in new scans to locate possible lettuce locations. Planting distance information was then used to localize the final lettuce positions. The algorithm was able to successfully locate 15 out of 16 sample lettuces.