Abstract: Methods, systems and apparatus are disclosed. A method of simultaneous localisation and mapping of a target environment responsive to a sequence of mono images of the target environment comprises providing the sequence of mono images to a first and a further neural network, wherein the first and further neural networks are unsupervised neural networks pretrained using a sequence of stereo image pairs and one or more loss functions defining geometric properties of the stereo image pairs providing the sequence of mono images into a still further neural network, wherein the still further neural network is pretrained to detect loop closures and providing simultaneous localisation and mapping of the target environment responsive to an output of the first, further and still further neural networks.