a method of building a locating service for a wireless network environment includes : an environment input step , a detection point calculation step , a measuring step and an assumed non - detected position point step to find measured position points and to measure a four - directional signal strength of the measured position point . by assuming signal strengths of non - detected position points , an entire positioning system can be established . a measuring process includes a portable device signal measuring step , a position point calculation step , and a signal feed back step to send the corresponding position information to the portable device to provide information to a user .