Time-frequency catalogue: JSON implementation and python library

TFCat (Time-Frequency Catalogue) is a data interchange format based on JSON (JavaScript Object Notation), which has been initially designed for exchanging low frequency radio events and features. It defines several types of objects how they are combined to represent related temporal-spectral features time spectrogram (a.k.a., dynamic spectrum), their properties, temporal spectral extents. This implementation inheriting from the GeoJSON file format. The python library implementing this specification provides software interface permitting create, update validate efficiently.