The ALPR matcher uses the "Common and contiguous characters" technique to improve plate read accuracy rate (sometimes called “fuzzy matching”).
You can configure how the ALPR matcher handles common and contiguous characters by modifying the MatcherSettings.xml file. For more information, see MatcherSettings.xml file.
- OCR equivalence (see ALPR matcher technique: OCR equivalence)
- Number of character differences (see ALPR matcher technique: Number of character differences)
The following settings are available when configuring common and contiguous characters:
- Necessary common characters
- The minimum number of characters that need to be common to both the first and second plate read. The characters must also appear in the same order in the plate, but not necessarily in sequence.
- Necessary contiguous characters
- Minimum character sequence length between the first and second plate read.
In overtime enforcement, there is an extra margin of error because the ALPR matcher is comparing a plate read against another plate read, not against a hotlist or permit list created by a person.
- OCR equivalence
- The OCR equivalents B and 8 are considered the same character and apply towards the common and contiguous character count.
- Five common characters
- Both reads have 5, A, B/8, C, and 3 in common, and they all appear in the same order. The “3” is not in sequence, but it respects the order.
- Four contiguous characters
- Both reads have 5, A, B/8, and C in sequence.
Plate read 5ABC113 does not match with SA8CH3 (example 3) because there are two OCR equivalents in the second read (S/5 and B/8). You allowed for only one OCR equivalent.
Using common and contiguous characters helps reduce the margin of error involved when both first and second plate reads are coming from the Sharp.