This value of -99 dB is a 'null' result, which means that no noise level could be calculated for that situation.
It does
not mean that the result was just very small.
There are many ways in which a null result can be generated, the most common are noted in the following list:
- The calculation position is inside a building envelope so a result cannot be calculated
- The receiver point cannot 'see' any noise source - none of the noise sources are within the angle of view of the receiver point
- There were no noise sources within the given cut-off distance
- There is no noise level for the particular combination of categories: for example, if Category 13 is for railway sources and you are looking at the results for CRTN calculations, Category 13 will have null results
- An error prevented a particular calculation from completing
- A particular receiver was excluded from the calculation list
You should carefully check to ensure that null results are correctly null and not the result of an error.
Future editions of NoiseMap will include improved tools for handling null results.
