The paper tackles the problem of estimating accurately the relative state of a CubeSat after in-orbit deployment using a camera. The objective is to provide quick and precise relative orbit information to support the ground operations during this critical phase. To that end, the separation sequence is captured by a camera whose images are processed on-ground to deliver accurate 3D pose estimate at the (sub) centimeter level. The resulting position measurements are dynamically filtered to reconstruct precisely the relative trajectory. Simulation results promise estimation of the velocity increment encountered during the deployment accurate to 0.2% and subsequent relative orbit prediction accurate at the meter level during the following hours.