Choosing the date of the forecast
Choice of displayed information and their representation
Tabs specific to each kind of forecast
Choosing the date of the forecast
Choice of displayed information and their representation
Tabs specific to each kind of forecast
ScanNav
Documentation
Grib Weather Module
The Grib Weather module of ScanNav lets you display weather forecasts overlaid on top of the chart. Here are the following types of weather information that can be handled today by ScanNav:
· Wind strength and direction
· Atmospheric pressures
· Water precipitations
· Air temperature
· Height of waves
The following screen shot shows an example displaying winds as feathers, pressures as curves, and swell as color filled areas.
The next example shows a display of winds as feathers, pressures as curves, and water precipitations as color filled areas.
Weather forecasts are available as GRIB standard format files. The good thing about this format is that it is quite condensed and can be easily downloaded from Internet with a slow connection such as cell-phones or radio. The weight of these file depend of course of the selected area and the different information available.
The GRIB functionality is provided as an optional module. The standard version of ScanNav lets you evaluate the module using a few determined samples. It is possible to extend these samples on request if you want to test with a particular grib file.
To obtain the GRIB extension license, the procedure is the same as for the standard license (see Obtaining a license). You just have to specify in your mail that you are subscribing for the Grib extension.
To activate the Grib option and display weather forecasts,
click on the button in the main
navigation toolbar (or select the “Grib weather” entry of the “Options” menu.
The following control window will be displayed, and if not the first time, the last selected grib file will be overlaid on the chart.
This window lets you control in a fast and easy manner the different weather information you want to display.
Open a file
selector to let you choose a new grib file from your disk where you downloaded
it.
: Lets you
pick in a list of previously displayed files to switch quickly between different
files (click on the left arrow). The text shows the actually displayed grib
file
Note: If you haven’t subscribed to the Grib extension, you
will not be able to open new files using the button, but
you may choose one of the predefined demo files in this list.
: This list
lets you choose a specific date & hour to display within the actual displayed
file available range. You can also move backward of forward step-by-step using
the two 
buttons below this
list.
· Days are expressed as Day/Month/Year
· Hours are expressed in GMT
· When changing file with the list, it opens at the nearest date to the actually displayed one if any file is active, or to the closest « today »’s date otherwise
·
When opening a new file using , it opens
at the nearest « today »’s date.
These buttons represent
the different weather forecast types that can be handled by ScanNav. By clicking
on them, a menu opens to let you choose quickly the type of information you
want to display.
The type of display currently active is represented on the left of each button with the following symbols:
« Feathers »
(for the wind): The wind strength and direction is represented with « feathers ».
This is a small graphic containing a main line giving the wind direction,
the head of this line being on the point of measure, with the wind going towards
it, and with branches indicating the strength at the other end, each full
branch representing 10 knots of wind and an eventual half branch representing
5 knots. As an example, 
indicates wind strength
of 35 Knots blowing from the 120°.
« Values »
(for other types): Other information than wind can be represented as text
values on the different points of measure.
« Curves »:
Information is shown as iso-value curves according to an interval defined
in the advanced options.
« Filled
area »: Information is shown as color filled area using a transparency
level defined in the advanced options.
« Scale »: Shows a scale of colors for the type of information in an independent window. Only minimum and maximum values are displayed in text so as not to overload the display. To view the value corresponding to a specific color, just move the cursor to the scale at the desired position, and a popup window will display the corresponding value. Scale windows automatically close if the corresponding information isn’t displayed in any form.
Notes:
- When a type of information is not available in the actual grib file, the corresponding button is grayed out (it is the case in the screen-shot above for the swell)
-
Each type of information can be represented
in several different ways. For example curves + filled area will give the
symbol 
. If a specific type
of information is represented with both “filled area” and “feathers”
(or values), the color of feathers will be inverted so as to keep them visible
on top of the filled area.
- Different type of information can be displayed using the same representation. For example you can choose to display both pressures and temperatures using curves, by gibing them different line width to distinguish them (see advanced options below). You must nevertheless take care not to overload the screen for the risk of being unreadable or confusing.
- The « filled area » mode can nevertheless be assigned to only one type of information at a time; the contrary wouldn’t make any sense…
When moving the cursor over the map, ScanNav calculates
interpolated values of the different available weather information under the
cursor, and displays them in the appropriate text fields at the bottom of
the control window. It is nevertheless possible to hide this part of the control
window so as to gain space on the screen by clicking on the 
button:
You just have to click on the 
button to display
this area again.
The 
button opens a Grib
settings dialog box letting you change advanced parameters either general
or specific to each type of weather information using different tabs.
This tab lets you configure parameters that are independent from the type of weather information.
· « Center chart on grib area »: When this box is checked, opening a new grib file centers and scales the map to display the entire area covered by the grib file.
· « Number of files in most recent list »: lets you specify a limit to the number of grib files showing in the history list for a quick selection.
· « Save the configuration » opens a dialog box letting you choose a place to save the actual GRIB settings so as to restore them later using « Restore a configuration ».
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Enter a name for the backup in the input field and click on OK. If you select an existing entry it will be overridden after a confirmation. The predefined « DefaultSetting » entry is reserved and cannot be overridden. To delete en existing entry, select it in the list and click on the “Delete” button. Nothing will be effective until you click on the “Ok” button. If you click on “Cancel”, the actual settings won’t be saved, but if you had previously “deleted” one or more entries, you will be prompt if you want to really delete them. |
The « Filled area » parameters are common to all type of weather information, as only one of these types can be displayed in this mode at a time.
· « None », « Winds », « Pressure », etc. determine the type of information you want to display as filled area. It acts the same as when using the buttons’ menus in the grib control window.
· « Transparency » lets you choose the level of transparency so as to view the map more or less across the grib filled areas. The more the cursor is on the right the more the grib information will be transparent and the map visible.
· « High quality »: Transparency uses some hardware and software resources that are quite recent in terms of technology, and that might not be present when running on old PC configurations. On recent hardware, this option should be checked. But on old hardware, transparency might be very consuming in terms of processor and result in a much too slow behavior. By un-checking this option, ScanNav will switch to an emulation mode of transparency which will let you gain a little on performances, at the cost of a lower rendering quality.
· « Color gradients »: This option only has effects on old hardware, where color gradients are only available by emulating them by software. The more this cursor is on the right the smother the gradients will be, but also the slower the performances. It has no effect on recent configurations.
· « Interpolation »: This option is useful in certain extreme cases where the grid step of the grib file is insufficient to give a regular aspect to color gradients between different area, that is when there are big differences of values between two adjacent points of the grid. This can be the case for precipitations as illustrated below.
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You can see that in the first case, the rain area is rather blur; It is much more clear in the second screen-shot, and again a little clearer in the third. But you have to take care that this is highly consuming in terms of performances, calculation times being multiplied by 2 to 3 for each mark of the ruler towards the right.
Furthermore, the result is mostly “esthetic”, the first case giving nevertheless a good idea of the perturbation. The difference for other forecast than precipitations are much less significant. It is therefore recommended to leave this parameter at its lower value (to the left), and to raise it only occasionally according to readability of information. This is actually a compromise between display quality and performances, left to the choice of the user.
You can adjust advanced parameters for each type of forecast in the appropriate tab. Except for a very few points, you will find the same type of parameters in each tab:
· « Wind feathers » (or « Values » for other type of data), and « strength curves » have the same meaning as through the menu displayed in the control window (see above).
· « Scale » (only in the wind tab) lets you parameterize the size of the wind feathers.
· « Line width » (only in the wind tab) lets you parameterize the thickness of the wind feathers.
· If « display curve labels » is checked, each curve will have a test label showing its value
· « Interval » lets you define the spacing of the curves in the given unit.
· « line width » lets you parameterize the thickness of the curves
· « Quality »: this lets you parameterize the smoothness of the curves, in the cases where the grid step defined in the grib file is insufficient to give smooth curves. As the “interpolation” parameter of the “general” tab, it is quite consuming in processor time. It is therefore recommended to leave this value at its lower value to the left. You might have to raise it a little if you notice some anomalies such as curves crossing each other or not closing properly.
· The « Colors » list lets you customize colors to your preferences. To change one of the values, select the corresponding entry in the list, and click on the colored button on the right. This will open a color chooser letting you give any value you want. Defined colors are “step” colors, ScanNav computes intermediate colors for values between these steps by mixing the colors so as to give a regular color gradient.
It is not possible in this version to change the interval of colors using the graphic interface. This might be possible in a future release. It is nevertheless possible for an expert to modify this parameter using the windows registry.
Warning: The following is given as information, and manipulations should be done by a windows expert, aware that a bad manipulation of the windows registry can cause dysfunctions on your windows system.
All information is saved in the windows registry. In the key « HKEY_CURRENT_USER\Software\Marc Lombard\ScanNav\Grib » you will find 5 sub-keys « Prec », « Press », « Temp », « Wind », and « HautHoule » respectively for precipitations, pressures, temperatures, wind, and swell.
In each of these keys you will find the following entries:
· « colorinterval »: lets you define the interval of values between each colors
· « minval »: gives the minimum value (every value lower or equal to this value will be assigned the first color)
· « ncolors »: gives the total number of colors (every value greater or equal to minval+ncolors*colorinterval will be assigned the last color)
To raise (or lower) the number of colors, you just have to change the « ncolors » value. Additional resulting entries will be assigned to black by default. You will just have to change these colors in the interface afterwards.
You can by the same mean raise or lower the minval and colorinterval values.
Each sub-key also have a key named « Colors » that contains the list of defined colors, as « col0 », « col1 », ... « colN ». These are defined as RGB values: 8 low order bits = Red, next 8 bits=Green, next 8 bits=Blue, 8 high order bits set to 0. It is possible to change them here, but more convenient and safe to do it using the interface described above.
No interpolation
Interpolation half
way 
Interpolation at
its maximum