Arithmetic processor, arithmetic processing method, and computer readable medium storing computer program

A processing method, comprising:

• obtaining observed data using a ranging device, the ranging device scanning a field which is present in front of the ranging device to obtain observed data of objects in the field;
• preparing, using a processor, a background candidate data memory that stores data as a background candidate, the data having an observation count of a number of times of obtaining the same observation data that is correlated with distance data representing the observed data;
• ranking, using the processor, a plurality of background candidates stored in the background candidate data memory based on the observation count as a basis to rank the plurality of background candidates stored in the background candidate data memory;
• comparing, using the processor, the observed data with distance data of a background candidate stored in the background candidate data memory to find a match between the observed data and the background candidate of the distance data, counting observations of the background candidate if there is a match, and replacing distance data of a lowest-ranked background candidate with the observed data in the absence of a background candidate matching the observed data, and setting the observation count to 1;
• processing, using the processor, the observation count as a basis to rank a plurality of background candidates stored in the background candidate data memory, the step being performed by the arithmetic processor;
• determining, using the processor, that there are M backgrounds if a duration during which the M background candidates are continuously ranked in a top N (M≤N) for a predetermined period, and selecting the M background candidates as backgrounds, the step being performed by the arithmetic processor;
• storing, using the processor, the background data in the background data memory;
• and
• calculating, using the processor, distances to the determined backgrounds.