Category: General Navigation

Cylindrical Projections Introduction to Cylindrical Projections Cylindrical Projections are made by wrapping paper in Cylindrical Shape around the Reduced Earth Paper touches reduced earth at the equator in a normal cylindrical projection Equator is the parallel of tangency or origin since the paper touches the reduced earth at the Equator Scale is correct only at equator since light travels correct length at equator Scale of Cylindrical Projections Scale of all perspective projections is correct at its parallel of tangency Scale is correct at the equator since it is the parallel…

Projections Introduction to Projections Projections are used to make maps and charts by projecting spherical (3D) earth on a paper (2D) Traditionally, map preparation was done in three steps Step 1 – A 3D transparent model of earth with latitudes and longitudes called reduced earth is made to scale Step 2 – Light is projected from inside the reduced earth on a wrapped photographic paper Step 3 – The wrapped paper is then cut opened to show latitudes and longitude Perspective projections are obtained by projecting light and are used…

Departure Departure Distance between two Meridians Departure is the distance between two meridians at a given parallel of latitude One minute of latitude would be one nautical mile along the equator and all meridians The rule does not apply to distances between meridians at other latitudes Distance between meridians is maximum at equator and reduces to zero at the poles Departure follows a cosine curve of latitude Parallels of latitude are rhumb lines hence it is a rhumb line distance Rhumb lines do not represent the shortest distance between two…

Convergence Conversion angle Convergency or Earth Convergence Convergency or Earth convergence is the angular difference between two meridians at a parallel of latitude Meridians converge towards the poles and diverge towards the equator At the equator, two meridians with 45 degrees of difference in longitude are parallel to each other Angular difference between the meridians is zero At the poles, the same two meridians with 45 degrees of difference in longitude are have an angle of 45 degrees Angular difference is same as their change in longitude At any other…

Scale of Chart Measurement of Distances using Scale of Chart Scale is the relationship between distances on chart and on ground The relation can be give as a Graduated Scale Line, Statement in Words and as a Representative Fraction Graduated scale line is a visual representation of scale on a graduated line Graduated scale lines are useful for visual estimation of distances Statement in words is the scale explained as a statement A statement of ‘One inch is equal to twenty nautical miles’ means a length of 1 inch on…

Navigation using Maps and Charts Topographical Maps Topographical Maps show natural and man-made features and are used for basic navigation Used for visual map reading during visual navigation Maps normally do not show radio navigation facilities since they are used for map reading during Visual Navigation Coverage of a maps are generally lesser than that of charts Aeronautical Charts Charts are used for Instrument or Radio Navigation Aeronautical Charts show Radio Navigation facilities and Air Routes since they are used for Instrument Navigation Coverage of a charts are normally much…