An easy to follow ROS node that could be used to calculate direct kinematics i.e. the end effectors transformation matrix [4x4] for Franka Emika Robot System Panda. The node can be modified for any robot with slight modifications in the code.
Panda’s kinematic chain
Denavit–Hartenberg parameters
Source and further information on Franka Control Interface (FCI): https://frankaemika.github.io/docs/control_parameters.html