In this post, we shall understand about the Position Reference System using a combination of Latitude and Longitude. In our previous posts, we had learnt about the Parallels of latitude and the meridians of longitude.
CARTESIAN CO-ORDINATE SYSTEM
The aim of this lesson is to understand the position reference system used for Air Navigation. Let us draw a parallel between the manner in which a point is uniquely defined on a flat or plane surface. You can draw a line on a flat piece of paper like Graph Sheet. The start point can be called as A and the end point can be called B.
These positions A and B can be defined along the X and Y axes. We can say that the position of A is defined by a combination of values along the X axis and the Y axis. Similarly, the position B can also be defined by values along the X and Y axis. Defining positions on a flat plane in this manner is referred as the Cartesian Coordinate System.
For the purpose of Air Navigation, we use similar method to define positions on the spherical shape of the earth. On the earth’s surface, we refer to coordinates using Latitude and Longitude in the place of X and Y axis, with a system of angular measurement.
GRATICULE
A position on earth’s surface is referred by a combination of its Latitude and Longitude named as the Graticule. By convention, the Latitude is quoted first and the Longitude quoted second in a Graticule. For example, Bangalore airport is at N1320 E07740. This indicates that the position is 13 Degrees And 20 Minutes North of the Equator and 77 Degree 40 Minutes East of the Prime Meridian. It needs to be remembered that Longitudes are measured from Greenwich meridian.
In summary, we have seen how Latitude and Longitude are used to precisely define position. The network formed by the Latitude and Longitude is referred to as a graticule. In the graticule, by convention Four Figure Latitudes are given first and Five Figure Longitudes are given next.
USE OF DECIMALS IN LATITUDE AND LONGITUDE
Some modern navigation systems use Latitude and Longitude with decimal places of minutes. Looking at our earlier example, N1320 E07740 could be written as N13.33 E077.66. You can see that 0.33 x 60 would be 20 minutes of Latitude and 0.66 x 60 would correspond to 40 minutes of Longitude.
Is it possible to travel from a place in Easterly Longitude to another place also in Easterly Longitude in a Westerly direction? Yes, it is possible. You should be able to clearly differentiate between a position in Easterly Longitude and direction of East.
Having learnt about defining a specific position we need to understand as to what happens to latitude and longitude when we travel from one place to another. In the next lesson, we shall understand the change of latitude while travelling from one place to another.