Technical aspects of data acquisition and display
The Impact of Electronic Charting on the Mariner
However fast the navigator might be capable of plotting his course the
fact is that by the time he has achieved it, the vessel is actually
somewhere else.
The overwhelming benefit of an electronic navigation chart is that it
can actually vary the display to suit the requirements of the actual
voyage. It can sense the computed depth against actual depth under
the vessel’s keel and, based on the draft of the vessel at the time, can
alert the mariner to his situation, not only positionally, but in actual
relationship with the bottom of the vessel.
When the advantages of digital radar are added, then it is easy to
represent other traffic in a region relative to the actual position of the
vessel.
Alarms sound (as they would have had such equipment been available
on the Exxon Valdez) if a “wheel over” is missed, if the vessel strays too
far from the planned path, if the vessel's path is projected into too
shallow water and if the vessel approaches too close for safety to the land
or a navigation aid. However clear this is though, since the image is
of a rasterised paper chart, “what you see is what you get”. Since the
mariner ultimately requires to make a “go or no go” decision we see
that vectorised data is “better” since data extraneous to the operation
of the vessel can be eliminated by switching it off. An example would
be all soundings and all imagery greater than 10 m deeper than the ship’s
draft.
We are starting to see emerging hybrid charts for ECDIS which provide a
combination of vector and graphic imagery.
Examine the image in figure 2. It represents a section of the Endeavour
Strait, which is within the Torres Strait and which is within the Great
Barrier Reef charting project detailed above.
Figure 3 illustrates the same area with ENC cells taking priority where
they have been finalised. Immediately, one can see the clarity of the presentation but before one gets the idea that such apparently simplistic
presentations of the chart information, one should examine figure 4
which presents the same area with all available underpinning information
displayed.
The strength of the ECDIS capability can be seen in these simplified
diagrams. The mariner’s decision-making is underpinned by a simplified
graphic which itself is underpinned by a strong database which is
capable of being interrogated intelligently by the mariner in a way
directly relevant to rhe particular circumstances of a particular voyage.
Margins of error are thus reduced and safety is enhanced.
145
The Impact of Electronic Charting on the Mariner
However fast the navigator might be capable of plotting his course the
fact is that by the time he has achieved it, the vessel is actually
somewhere else.
The overwhelming benefit of an electronic navigation chart is that it
can actually vary the display to suit the requirements of the actual
voyage. It can sense the computed depth against actual depth under
the vessel’s keel and, based on the draft of the vessel at the time, can
alert the mariner to his situation, not only positionally, but in actual
relationship with the bottom of the vessel.
When the advantages of digital radar are added, then it is easy to
represent other traffic in a region relative to the actual position of the
vessel.
Alarms sound (as they would have had such equipment been available
on the Exxon Valdez) if a “wheel over” is missed, if the vessel strays too
far from the planned path, if the vessel's path is projected into too
shallow water and if the vessel approaches too close for safety to the land
or a navigation aid. However clear this is though, since the image is
of a rasterised paper chart, “what you see is what you get”. Since the
mariner ultimately requires to make a “go or no go” decision we see
that vectorised data is “better” since data extraneous to the operation
of the vessel can be eliminated by switching it off. An example would
be all soundings and all imagery greater than 10 m deeper than the ship’s
draft.
We are starting to see emerging hybrid charts for ECDIS which provide a
combination of vector and graphic imagery.
Examine the image in figure 2. It represents a section of the Endeavour
Strait, which is within the Torres Strait and which is within the Great
Barrier Reef charting project detailed above.
Figure 3 illustrates the same area with ENC cells taking priority where
they have been finalised. Immediately, one can see the clarity of the presentation but before one gets the idea that such apparently simplistic
presentations of the chart information, one should examine figure 4
which presents the same area with all available underpinning information
displayed.
The strength of the ECDIS capability can be seen in these simplified
diagrams. The mariner’s decision-making is underpinned by a simplified
graphic which itself is underpinned by a strong database which is
capable of being interrogated intelligently by the mariner in a way
directly relevant to rhe particular circumstances of a particular voyage.
Margins of error are thus reduced and safety is enhanced.
145