Feb 19, 2020
Navigating Safely: Understanding your chart plotter
Chart plotters, mobile phone apps, and
It’s important to remember that electronic equipment can fail and
Make sure you know the limitations of the type of chart your plotter uses. For
Some plotters are almost ‘plug and play’ while others will require some technical nous to set up. For
Plotters combine the position information provided by the GPS receiver with the vessel’s position superimposed on an electronic representation of a chart. It’s important for users to understand that there are two fundamentally different types of charts used on plotters: ‘Raster’ and ‘Vector’.
Raster chartsRaster charts are a ‘scanned’ copy of a paper chart. Raster charts look the same as paper charts and contain the same information. While you can ‘zoom in’ and increase the size of the chart image, you are still working with the same image (resolution and scale) of the original chart. Zooming in is essentially like looking at a paper chart through a magnifying glass.
Raster charts are ‘quality assured’; they are copies of existing charts and are produced by the relevant national hydrographic office. In NZ you can source raster charts free of charge via the LINZ website – coupled with open source software you can turn your laptop into a plotter
VectorInstead of being a scanned copy of a paper chart, vector charts can be visualised as layers of digital information stored in a database, displayed on a screen providing a representation of a chart. The fundamental difference is that vector charts can be ‘zoomed’ in or out to a far greater extent.
The display can also be customised, with layers of information added or taken away. For example, you may wish to remove depth sounding figures above a certain value (e.g. not show depths greater than 10m), or remove all place names to reduce clutter. Be cautious that you haven’t de-selected vital information!
Many Vector charts are also produced in conjunction with hydrographic departments and so come with a ‘quality assurance’ – but be aware, not all come with this guarantee of accuracy.
Electronic Chart CorrectionsTo be reliable, electronic charts, just like the paper versions, must be kept up to date. How up to date are your electronic charts? Some suppliers will give you free updates while others may have a fee. Charts for mobile devices may be updated automatically and some fixed units provide a blue tooth or Wi-Fi system for updates.
And finally - don’t forget that good old paper charts are still produced and are an inexpensive ‘
For more on the basics of navigation checkout our website at www.boatingeducation.org.nz or call 09 361 4700 for more information.