Portable terminal apparatus with auto caliblation of orientation measurement

An offset calibration method performed in a portable terminal apparatus being mounted in a casing and having a magnetic sensor which detects a magnetic field around the casing with an offset and outputs magnetic data representing the detected magnetic field and a tilt sensor which sequentially detects a tilt of the casing and outputs tilt data representing the detected tilt, the offset calibration method comprising the steps of:

• sequentially capturing the magnetic data from the magnetic sensor at a given time interval;
• calculating the offset of the magnetic sensor based on a plurality of the sequentially captured magnetic data;
• detecting an orientation variation of the casing based on the tilt data sequentially outputted from the tilt sensor;
• and
• changing the time interval for sequentially capturing the magnetic data in accordance with the detected orientation variation.

A machine readable medium for use in a portable terminal apparatus being mounted in a casing and having a processor, a magnetic sensor which detects a magnetic field around the casing with an offset and outputs magnetic data representing the detected magnetic field, and a tilt sensor which sequentially detects a tilt of the casing and outputs tilt data representing the detected tilt, the machine readable medium containing a program executable by the processor for causing the portable terminal apparatus to perform an offset calibration method comprising the steps of:

• sequentially capturing the magnetic data from the magnetic sensor at a given time interval;
• calculating the offset of the magnetic sensor based on a plurality of the sequentially captured magnetic data;
• detecting an orientation variation of the casing based on the tilt data sequentially outputted from the tilt sensor;
• and
• changing the time interval for sequentially capturing the magnetic data in accordance with the detected orientation variation.