A device (300a, 300b), comprising: - a communication link to a first sensor (310a, 310b), said first sensor being located within a housing carriable by a pedestrian, configured to obtain measured values of a first set of data representative of a speed of the pedestrian, or a derivative thereof; - a communication link to a second sensor (320a, 320b), said second sensor being located within a housing carriable by the pedestrian, configured to obtain measured values of a second set of data representative of an altitude of the pedestrian, or a derivative thereof; - a processing logic (330a, 330b) configured to calculate estimated values of a state vector of the pedestrian comprising: o a first element representative of the speed of the pedestrian, or a derivative thereof; o a second element representative of the altitude of the pedestrian, or a derivative thereof; o and a path slope; said processing logic being configured to calculate estimated values of the state vector based on said measured values of the first set of data said measured values of the second set of data, and a model of the pedestrian motion comprising a relationship between at least a speed of the pedestrian or a derivative thereof and a path slope or a derivative thereof, wherein a state transition model is expressed by a transition matrix: ν k α k p a, k p s, k = 0 f 1 0 0 0 1 0 0 f 2 f 3 f 4 f 5 0 0 0 1 ν k − 1 α k − 1 p a, k − 1 p s, k − 1 wherein the speed v k of a user at time step k is calculated based on the path slope at time step k-1, and the Tobler's hiking function: ν k = K Tobler ∗ 6 ∗ e − 3.5 ∗ abs tan α k − 1 + 0.05 + w ν, k w v,k is the process noise at time step k, related to the speed of the pedestrian, wherein: α k = α k − 1 + w α, k α k is the path slope at time step k, w α,k is the process noise at time step k, for the path slope, wherein: p a, k = p a, k − 1 + p s, k − 1 ∗ 1 − 0.0065 ∗ ν k − 1 ∗ ΔT ∗ sin α k − 1 T 0 k 5.255 − p s, k − 1 + w p a, k p a,k is the variation at time step k of the pressure due to altitude, w p a,k is the process noise at time step k for the altitude pressure, T 0 k is a temperature measured at time step k, v k * ΔT * sin ( α k -1) provides an estimated variation of the altitude of the pedestrian, wherein: p s, k = p s, k − 1 + w p s, k p s,k is the static pressure at time step k, w p s,k is the process noise at time step k, for the static pressure. - a communication link to a first sensor (310a, 310b), said first sensor being located within a housing carriable by a pedestrian, configured to obtain measured values of a first set of data representative of a speed of the pedestrian, or a derivative thereof; - a communication link to a second sensor (320a, 320b), said second sensor being located within a housing carriable by the pedestrian, configured to obtain measured values of a second set of data representative of an altitude of the pedestrian, or a derivative thereof; - a processing logic (330a, 330b) configured to calculate estimated values of a state vector of the pedestrian comprising: o a first element representative of the speed of the pedestrian, or a derivative thereof; o a second element representative of the altitude of the pedestrian, or a derivative thereof; o and a path slope; o a first element representative of the speed of the pedestrian, or a derivative thereof; o a second element representative of the altitude of the pedestrian, or a derivative thereof; o and a path slope; said processing logic being configured to calculate estimated values of the state vector based on said measured values of the first set of data said measured values of the second set of data, and a model of the pedestrian motion comprising a relationship between at least a speed of the pedestrian or a derivative thereof and a path slope or a derivative thereof, wherein a state transition model is expressed by a transition matrix: ν k α k p a, k p s, k = 0 f 1 0 0 0 1 0 0 f 2 f 3 f 4 f 5 0 0 0 1 ν k − 1 α k − 1 p a, k − 1 p s, k − 1 wherein the speed v k of a user at time step k is calculated based on the path slope at time step k-1, and the Tobler's hiking function: ν k = K Tobler ∗ 6 ∗ e − 3.5 ∗ abs tan α k − 1 + 0.05 + w ν, k w v,k is the process noise at time step k, related to the speed of the pedestrian, wherein: α k = α k − 1 + w α, k α k is the path slope at time step k, w α,k is the process noise at time step k, for the path slope, wherein: p a, k = p a, k − 1 + p s, k − 1 ∗ 1 − 0.0065 ∗ ν k − 1 ∗ ΔT ∗ sin α k − 1 T 0 k 5.255 − p s, k − 1 + w p a, k p a,k is the variation at time step k of the pressure due to altitude, w p a,k is the process noise at time step k for the altitude pressure, T 0 k is a temperature measured at time step k, v k * ΔT * sin ( α k -1) provides an estimated variation of the altitude of the pedestrian, wherein: p s, k = p s, k − 1 + w p s, k p s,k is the static pressure at time step k, w p s,k is the process noise at time step k, for the static pressure.