Method of determining a direction of a drilling pattern in a tunnel curve calculation to be executed in a control unit of a rock drilling rig, a storage device including software product implementing the method and a rock drilling rig. Tunnel line of a tunnel to be excavated is determined. Location of a drilling site on the tunnel line is communicated to the control unit and a navigation plane of the drilling pattern is positioned on the tunnel line. Start point of a round is positioned on the tunnel line and length of the round is provided. End point of the round is positioned at a distance corresponding with the length of the round from the start point and a coordinate system of the drilling pattern is directed so one of its axes points from the start point to the end point. Finally, different coordinate systems are transformed.