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The system was developed partly because access to foreign government-controlled global navigation satellite systems is not guaranteed in hostile situations, as happened to the Indian military in 1999 when the United States denied an Indian request for Global Positioning System (GPS) data for the Kargil region, which would have provided vital information. [22]
Name used in the default map caption; image = India location map.svg The default map image, without "Image:" or "File:" image1 = India relief location map.jpg An alternative map image, usually a relief map, which can be displayed via the relief or AlternativeMap parameters; top = 37.5 Latitude at top edge of map, in decimal degrees; bottom = 5 ...
An interval time of week (ITOW): the integer number of 2 hour periods elapsed since the latest start/end of week. It has range 0 to 83 (inclusive), requiring 7 bits to encode. A time of interval (TOI): the integer number of 18 second periods elapsed since the period represented by the current ITOW to the beginning of the next message. It has ...
Name used in the default map caption; image = Chennai area locator map.svg The default map image, without "Image:" or "File:" top = 13.295 Latitude at top edge of map, in decimal degrees; bottom = 12.844 Latitude at bottom edge of map, in decimal degrees; left = 80 Longitude at left edge of map, in decimal degrees; right = 80.3575
A computer continually calculates the vehicle's current position. First, for each of the six degrees of freedom (x,y,z and θ x, θ y and θ z), it integrates over time the sensed acceleration, together with an estimate of gravity, to calculate the current velocity. Then it integrates the velocity to calculate the current position.
The basic formula for DR is Distance = Speed x Time. An aircraft flying at 250 knots airspeed for 2 hours has flown 500 nautical miles through the air. The wind triangle is used to calculate the effects of wind on heading and airspeed to obtain a magnetic heading to steer and the speed over the ground (groundspeed).
The drift angle (shaded red) is due to the wind velocity (W/V, in green). In navigation, the heading of a vessel or aircraft is the compass direction in which the craft's bow or nose is pointed. Note that the heading may not necessarily be the direction that the vehicle actually travels, which is known as its course.
The angular velocity of the Earth is defined to be ω = 72.921 15 × 10 −6 rad/s. [ 11 ] This leads to several computed parameters such as the polar semi-minor axis b which equals a × (1 − f ) = 6 356 752 .3142 m , and the first eccentricity squared, e 2 = 6.694 379 990 14 × 10 −3 .