A localization server improves position estimates of global navigation satellite systems (GNSS) using probabilistic shadow matching and pseudorange matching is disclosed herein. The localization server may utilize one or more of the following information: the locations of the satellites, the GNSS receiver's location estimate and associated estimated uncertainty, the reported pseudoranges of the satellites, the GNSS estimated clock bias, the SNRs of the satellites, and 3D environment information regarding the location of the receiver. The localization server utilizes a Bayesian framework to calculate an improved location estimate using the GNSS location fixes, pseudorange information, and satellite SNRs thereby improving localization and tracking for a user device.