Filtering device and environment recognition system

A filtering device, comprising one or more processors, configured to:

• derive, for a pair of comparison targets having mutual relevance, multiple evaluation values indicative of correlations between an extracted part that is selectively extracted from one of the comparison targets and multiple extracted parts extracted from the other comparison target, respectively;
• set a reference waveform part of a transition waveform comprised of the multiple evaluation values, the reference waveform part containing the evaluation value with the highest correlation;
• determine whether the transition waveform contains one or more parts that are similar to the reference waveform part, and determine, based on the result of the determination, whether a difference value for the evaluation value with the highest correlation is valid as the difference value;
• and
• select as the reference waveform part one of two parts of the transition waveform that are located from (1) a first inflection point at which the evaluation value has the highest correlation to (2) second and third inflection points before and after the first inflection point in horizontal directions at which inclinations of the transition waveform become zero for the first time, respectively, the part selected as the reference waveform part being the one of the two parts having a larger difference between the evaluation value of the first inflection point with the highest correlation and an evaluation value of either one of the second and third inflection points.