Position-verified access apparatus, method, and program product

A method comprising:

• receiving a device distance and a device position from a position detecting device which measures the device distance from the position detecting device to each of a plurality of satellites and calculates the device position that is the position of the position detecting device based on the device distance and the position of each of the plurality of satellites;
• calculating a verification position that is the position to be calculated by the position detecting device, based on the received device distance and the position of each of the plurality of satellites at the time of measuring the device distance;
• calculating a distance that is the distance between the position of each of the plurality of satellites at the time of measuring the device distance by the position detecting device and the received device position;
• and
• judging that the device position detected by the position detecting device is valid, on condition that the device position is coincident with the verification position and that the received distance differs from the calculated distance by a predetermined difference value or more.

A product comprising:

• a computer usable medium having computer readable program code stored therein, the computer readable program code in said product being effective to:
• receive a device distance and a device position from a position detecting device which measures the device distance from the position detecting device to each of a plurality of satellites and calculates the device position that is the position of the position detecting device based on the device distance and the position of each of the plurality of satellites;
• measure the device distances between the position detecting device and each of the plurality of satellites, based on a time elapsed since each of the plurality of satellites transmits a signal and until the position detecting device receives the signal;
• calculate a verification position that is the position to be calculated by the position detecting device, based on the received device distance and the position of each of the plurality of satellites at the time of measuring the device distance, wherein the verification position is calculated based on an equation, for each of the plurality of satellites, whose unknowns are a clock error of the position detecting device and each element of the vector showing the coordinates of the device position, the equation showing that the distance to the satellite measured by the position detecting device, plus the clock error multiplied by the signal velocity, is equal to the distance calculated based on the position of each of the plurality of satellites and the device position;
• and
• judge that the device position detected by the position detecting device is valid, on condition that the device position is coincident with the verification position and that the received distance differs from the calculated distance by a predetermined difference value or more.