Tham khảo tài liệu 'mobile robots perception & navigation part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Symbolic Trajectory Description in Mobile Robotics 551 5. Fresco construction The first step of the fresco construction gathers the landmarks space into ordered series of semantic clues and describes the environment by positioning landmarks in respect to each others. Each landmark has exactly two neighbours the last landmark in the list has the first one as second neighbour . Building the fresco is made using the symbols presented in Table 1 which gathers the landmarks identity and attributes. The landmarks identity and attributes have been chosen according to the indoor environment in which the robot moves. This operation mainly aims at eliminating the notion of distance to the profit of a spatial series and highlights the qualitative representation of the environment. An example of fresco is given in fig. 4f. The robot is situated in the middle of the environment. To each landmark are associated three qualitative attributes representing three properties of landmarks. The off-sight attribute is set when the landmark stands close to or beyond the end of the sensor range. The position attribute can take the following values crosswise diagonal or lengthwise according its position related to the lenghtwise and crosswise robot axis. The certainty attribute is introduced to take into account landmarks whose evolution can be forecast. It is false for every landmark for instance diagonal End_of_Closure 45 _angles that could come from a possible noise introduced in the digitisation process and whose evolution cannot be known Pradel al. 2000 Pradel Bras 2001 . Fig. 4. Example of the digitised constructions a upper left real world from raw measurements b upper centre reoriented cellular space c upper right refined space after superfluous data elimination d lower left Angles_of_Closure extraction e lower centre End_of_Closure extraction f lower right fresco construction 552 Mobile Robots Perception Navigation Symbol Landmark Position Off-sight Certainty Angle_of_Closure True
