374
Apps
• GPS is a service operated by the USA
Department of Defense, so the GPS radio
wave condition may be controlled (accuracy
degraded, radio wave suspended, etc.) for
reasons of US national security. And, wave
conditions differ by satellite locations;
therefore, positioning operations in the same
location under the same environmental
conditions may not yield the same result.
• Some wireless communications products
(mobile phone, data detectors and some
others) block satellite signals and also cause
instability of signal reception.
• Some map displays based on location
information (latitude/longitude information)
may be not accurate due to some countries' or
regions' regulations.
■
Where radio waves are difficult to receive
Note that radio waves may not be received or
it may be difficult to receive radio waves in the
following conditions, since GPS uses radio
waves from a satellite.
• Inside or immediately under a building
• Inside a basement or tunnel, and below the
ground or water
• Inside a bag or box
• Building area or residential area
• Inside or under a thick covering of trees
• Near a high-voltage cable
• In a car, inside a train compartment
• Bad weather such as heavy rain or snow
• When there are obstructions (people or
objects) near the terminal
