![]() Most often, distortions are scarcely noticed when this projection is used to chart a small area. ![]() So, strictly speaking, a straight course will not appear as a straight line in the chart, but the parallels remain perpendicular to the meridians. On this chart parallels appear as slightly curved and also the meridians converge at high latitudes. An important one is the stereographic projection, which is constructed by projecting the globe on a flat plane instead of a cylinder. The result is that both A – A' and B – B' are now as long as the bottom of the chart and are “too long”.īut there are of course other projections in use by yachtspersons. If you divide the surface of the earth in eight pieces, and lift one out and project it, you end up with the figure on the left. The horizontal scale is only valid for one latitude in the chart and can therefore only be used for the coordinates (a point, but not a line). So, distances – in degrees, or in miles and minutes – should not only be read on the vertical scale, but also at approximately the same height. The two little navy coloured markers have precisely the same size, the upper one measures only 0.64 degrees (= 38.4 NM) while the other measures 1.00 degrees (= 60 NM). The vertical scale depicted on the right demonstrates the distortion. From this it is clear that only the vertical scales should be used for measuring distances. ![]() The figure below shows the construction of the Mercator projection. Yet, on the chart they have exactly the same length creating a misrepresentation which gets bigger nearer to the poles. Subsequently, look at a high parallel: the length / circumference of such a parallel – a small circle – on the globe is much smaller than the equator. However, whereas the meridians converge on the globe they run parallel in the projection (see chart below), indicating the distortion. On this cylinder the surface of the earth is projected and finally the cylinder is cut open to yield the 2-dimensional chart. The Mercator chart was designed for sailors and can be constructed by wrapping a cylinder around the planet so that it touches the equator. Moreover, the meridians will need to be perpendicular to the parallels.Ī well known method to create such a chart is called the Mercator projection after Gerard “ Mercator” Kremer, a Flemish scholar who studied in 's Hertogenbosch (the Netherlands) and Leuven (now Belgium) and who invented his famous projection in 1569. To fulfil these demands a nautical chart requires parallels and meridians that are both straight and parallel. a straight course should appear as a straight line in the chart.the angles between three objects in the chart should be the same as the angles between the real objects which they represent.Both forms are 2-dimensional representations of a 3-dimensional world which will result in various distortions, yet as long as two requirements are met we can use the 2-dimensional image for navigational purposes: Before working with electronic charts (C-MAP, Navionics, BA) it is essential to understand and work with paper charts.
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