Orekit provides two tropospheric models (Marini-Murray and Saastamoinen) that need weather parameters inputs. In the case of the user does not have access to weather data, standard atmosphere initialization is possible. However, it can be useful to implement weather models that allow the computation of the weather parameters thanks to the station position (latitude, longitude and altitude) and the date. One of these models is GPT (Global Pressure and Temperature). It was developed by the Vienna University.

More information about these models can be found at: GPT