Abstract: A high frequency heating method of a bolt sets a maximum achievable temperature Tmax in an inner surface of the bolt with hole to a value which is not higher than a final heat treated temperature To. A maximum thermal stress .sigma.max occurring in the bolt with hole is set to a value which is not more than a yield stress .sigma.ys of the bolt material. From the maximum thermal stress .sigma.max, a temperature difference .DELTA.T is obtained between Tmax and a mean temperature Tmean along an entire cross section of the bolt, under the condition that .DELTA.T is to be not more than a permissible maximum temperature difference .DELTA.To obtainable from the yield stress of the material. The maximum suppliable power by Tmax, .DELTA.T and dimensions of the bolt are obtained, and then a heater is inserted into a small diameter hole of the bolt with hole and the maximum suppliable power, which value is obtained by the above operation, is supplied to the heater so that the bolt with hole is heated to be elongated.

Abstract: A navigation system for an automotive vehicle includes a map data storage unit. The storage unit stores first known target points and adjoining target points preselected for each of the first target points from the first target points. The storage unit further stores a first data group associated with each of the first target points. Each of the first data groups includes a second data group corresponding to each of the adjoining target points of the corresponding first target point. Each of the second data groups includes an abstract configuration of the corresponding first target point and a travel information required at the corresponding first target point for going to the corresponding adjoining target point. The system selects second target points from the first target points to define a vehicle travel route. The system further selects one of the second data groups based on third and fourth target points selected from the second target points.