In a prior art method, see SE 460077 or the corresponding CA 1322968, one uses two ultrasonic transmitters placed on a feed beam and three microphones which have been placed in a plane with the aid of a laser beam and a rotatable goniometer. The position of the microphone plane along the laser beam is measure by a measuring tape.

The present invention, which is defined in the subsequent claim, aims at achieving a simplified method where the local coordinate system of the rock drilling rig is connected to the coordinate system of the rock body. Through this one manages with one orientation for a whole round.

An embodiment of the invention is described below with reference to the accompanying drawing in which fig 1 shows a screen picture with a level in a mine. Fig 2 shows a screen picture with a part of the level according to fig 1. Fig 3 shows a rock drilling rig with a feed beam oriented with the aid of a laser beam.

At the planning office of the work site a data file defining the rock volume to be blasted is given and which can be handled by the control system of the rock drilling rig. This information about desired volumes for blasting is stored in the memory of the rock drilling rig. In order to orient the rock drilling rig the operator first chooses a level and then an area 1 of this level. The result of these choices is presented for the operator on the ordinary display of the rock drilling rig as shown in fig 1. In the shown example the level is 1015 and the area AVOS. Then front and rock face where the rig is situated is chosen. When this has been done a picture according to fig 2 is shown. The operator then adjusts horisontal and vertical angles and the distance for the navigation laser used. The position 2 of the laser beam and the rock face 3 are now drawn on the display. In order to connect the local coordinate system 4 of the rock drilling rig to the coordinate system of the rock body a boom 5 on the rock drilling rig 4 is driven such that a feed beam 6 is oriented with the aid of the laser beam 2. When this has occurred the control system of the rock drilling rig knows where the rock drilling rig is situated in the coordinate system of the rock body.

After this it is possible in a simple and efficient way to drill and blast the desired rock volume defined in the coordinate system of the rock body.