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<html><head><title>XQCT - Marine chart viewer</title>
</head><body>
<h1>XQCT - Marine Chart Viewer</h1>
<h2>Introduction</h2>
<p>This program displays marine charts of the UK with tide information
overlaid.
</p>
<h2>Tide Information</h2>
<p>There are two types of symbols overlaid on the chart: bars which display
the current tidal level and arrows which display the current tidal direction
and speed. As the time is changed the tidal levels and directions also
change.
</p>
<p>Tidal levels are shown as a box where the bottom is the mean low water
level on a spring tide and the top is the mean high water level on a spring
tide. The bar across the middle shows the current tide level at the chosen
time. The current level may be above or below the high/low marks because
the values come from different sources. The high/low marks are taken from
the Admiralty charts and the current mark is calculated mathematically and
so they may be on different datums (ie. the baseline is different).
More information about a Tidal Level can be obtained by right-clicking on it
and selecting its name from the context menu.
</p>
<p>Tidal directions are shown at points known as Tidal Diamonds. These
are points where the speed and direction of the current can be calculated
at the chosen time. You will see that as the time approaches high water
the length of the arrow reaches a maximum and as the time approaches low
water the length of the arrow is at its shortest. These points are known
as slack water. As the tide turns the direction of the arrow changes from
predominantly one way to predominantly the opposite direction. However at
low tide slack water the arrow may point at intermediate directions. This
does not mean the current is flowing in that direction; it is simply an
artefact of the way the calculations are performed. Be careful when reading
directions at this time.
More information about a Tidal Diamond can be obtained by right-clicking on it
and selecting its name from the context menu.
</p>
<p>Please note that the length of the arrow at high tide will change
throughout the week. On a spring tide the high water mark is at its highest
which means that more water has flowed in and thus the current is stronger.
On a neap tide the current is weaker. The length of the arrow indicates the
speed of the current (it is directly proportional to the speed in knots) so
it follows that at spring tides it will be longer than at neap tides.
</p>
<h2>Changing the chart</h2>
<p>A new chart can be loaded from the option in the File menu.
A list of recent charts is available for quick access to the last ten displayed.
A new chart can also be chosen by right-clicking to get a context menu at
any point on the chart. A menu will display all the other charts which cover
the location where the mouse clicked.
</p>
<h2>Moving around the chart</h2>
<p>Use the scroll bars to move around a chart which is larger than the screen.
The mouse wheel cannot be used to scroll up or down because it is used to
zoom instead. It is better to simply press the mouse button on the chart
and drag it around. If you are moving the mouse when the mouse button is
released the chart will continue to move in the same direction, just like
spinning a globe. To stop the movement simply click (press/release) the
mouse button on the chart. To prevent the movement just hold the mouse steady
briefly before releasing the button.
</p>
<h2>Zooming in or out</h2>
<p>The options in the View menu can be used to display the chart
zoomed in to full resolution or zoomed out to half, quarter or eighth
resolution. The same effect can be achieved using the mouse wheel.
</p>
<h2>Changing the date/time</h2>
<p>To change the starting date use the option in the Edit menu.
The display changes to show the tide conditions at the time 00:00
on the specified day.
Use the slider underneath the chart to change the time.
It moves in 15 minute intervals using the left/right cursor keys
or hourly intervals using the page-up/down keys.
It can be dragged to any time, up to a maximum of 3 days from the
starting date.
</p>
<h2>Saving the chart</h2>
<p>The chart can be saved using the option in the File menu.
This will save the whole chart, but only the chart, not the tidal
information. If you want the tidal information too then print it.
</p>
<h2>Printing the chart</h2>
<p>The chart can be printed using the option in the File menu.
This will print the section of the chart which is currently visible
in the window. It will also have the tidal information overlaid,
and the chosen date and time in the top left corner. The page will
be landscape or portrait automatically as appropriate for the window
size.
</p>
<h2>Author</h2>
<p>Andrew Brooks <[email protected]> July 2010</p>
<hr>
<h2>Acknowledgements</h2>
<p>The tidal level information has been read from Admiralty charts.
The tidal stream information has been read from Admiralty charts.
The tidal calculations are performed internally by the software.
The tide tables are provided by a mixture of sources including: xtide,
wxtide32, and other internet sources. The tide calculations are
performed externally by the xtide program. The libtcd library is
used internally to find the locations of tide stations. The
kautoconfig library is used internally for configuration.
</p>
<!-- Document version 1.01 arb Fri Jul 30 19:08:56 BST 2010 -->
</body></html>