Abstract: Broadly speaking, this disclosure generally relates to methods, systems and apparatuses for performing monocular depth estimation, i.e. depth estimation using a single camera. In particular, this disclosure relates to a method for generating a training dataset for training a machine learning, ML, model using federated learning to perform depth estimation. Advantageously, the method to generate a training dataset enables a diverse training dataset to be generated while maintaining user data privacy. This disclosure also provides methods for training the ML model using the generated training dataset. Advantageously, the methods determine whether a community ML model that is trained by client devices needs to be retrained, and/or whether a global ML model, which is used to generate the community ML model, needs to be retrained.