Navigator Light Software

Navigator=20 4.5 user manual

Table of = contents

The access=20 window

>> Chapter 1 - Celestial=20 Navigation

Preparing the = sky=20
The twilights<= /FONT>=20
Taking altitude= s=20
The meridian passage = for the Sun=20 (noon sight)=20
Better=20 meridian passage=20
Using artificial horizons=20
Print your own Nautical Almanac pages=20

>> Chapter 2 - Star=20 Finder

>> Chapter 3 - Chart=20 Navigation

Vector=20 and raster charts
Using raster=20 images
Printing= =20 chart images=20
Chart tools=20
Navigator desktop=20 files
Using the GPS=20 interface
Troubleshoot= ing=20 the GPS connection
The Leg=20 calculator

>> Chapter 4 - ChartMaker<= /P>

How it works=20
Mercat= or=20 latitude scale correction=20
Which=20 images can be used ?=20
Tips for scanning=20 charts=20
Choosing the 3 refer= ence=20 points=20
Importing a raster=20 chart image=20
Making vector=20 charts

Celestial Navigation links=20

New to celestial navigation? To = understand=20 how it works, go to the Fundamentals=20 page.=20
Other Navigator screen=20 shot=20
Navigator software Homepage=20

The access = window=20

back to the=20 top

Both Navigator and ChartMaker programs have = access=20 windows. These are the main menus of these applications. = From the=20 access window you choose the module you want to work = with.

For Navigator you have the following options=20 (buttons):

Chart Navigation=20
Celestial Navigation=20
Star Finder

For ChartMaker:

Make vector chart=20
Import chart image

Take some time to read the License Agreement and = disclaimer=20 (click "important information"). Closing the access window = will=20 terminate the program.

Chapter=20 1 - Celestial Navigation

to table of=20 contents

The goal of the celestial navigation is to find the=20 astronomical position, the position of the = boat. In=20 this section we will see how this can be done with the help = of=20 Navigator software. As we have seen in the fundamentals,=20 crossings of two or more Lines of Position, taken for two or = more=20 celestial objects, define this position.

Preparing = the sky=20

back to the=20 top

But before you start taking altitudes of celestial = objects, you=20 must be able to find them with the sextant. Trying to find a = star=20 with the sextant on a rocking boat is not easy The eyepiece = has a=20 relatively small angle of view and the sight is twisted by = the=20 sextant mirrors.

One technique to find a star is to turn the sextant = upside down,=20 point it to the star, and bring the horizon by adjusting the = arm.

Better yet is to know the approximate altitudes and = azimuths of=20 the stars you are going to observe. This is known as = preparing=20 the sky.

The = twilights

back to the=20 top

Navigators wake up early. They do so to take advantage of = the two=20 times of the day when the sky is in best condition for = celestial=20 navigation: the twilights. In the civil twilights - = times=20 when the sun is 6=B0 below the horizon - it's dark enough to = see the=20 stars and planets, and light enough to see the horizon. This = happens=20 before sunrise and after sunset.

The first step of the sky preparation is to determine the = time of=20 the twilights.

To calculate the times of twilights do:

Select the Sun in the celestial objects = listbox.=20
Set the date of the observation. Since you are = probably going=20 to prepare the sun in the night before, set the date to = the=20 following day.=20
Set the assumed position (Latitude and Longitude). = It's the=20 position you think you are going to be in the time of the=20 observations.=20
Select the tab "Other calculations"=20
Press "Object data" button.

The last two lines show the time of twilights. Like this: =

dawn civil twilight: 9:13  GMT
Set  civil twilight: 20:46  GMT

Selecting = stars and=20 planets

back to the=20 top

Now that we know the twilight times, you can select the = celestial=20 objects you are going to observe. At any time, = Navigator=20 gives you more than 33 celestial objects to choose from. Of = course=20 you will only need 4 or 5. To select stars and planets you = will=20 observe, follow these guidelines:

Select stars and planets that you are most familiar = with.=20
Select the brighter objects. Planets are easier to = spot,=20 because they are very bright. Some stars are also very = bright and=20 easy to find. Some constellations have distinct look and = are=20 easier to locate.=20
Select objects with altitudes between 30=B0 and 60=B0. = Less than=20 that you result in greater atmospheric refraction error, = which is=20 not easy to correct (because it depends changing on = atmospheric=20 conditions). And altitudes higher than 60=B0 are more = difficult to=20 measure.=20
Do not select stars that have similar azimuths or that = are in=20 opposition. The resultant Lines of Position will be nearly = parallel, which is undesirable.

To prepare the sky do:

Set date and twilight time of your next observation.=20
Set the assumed position (Latitude and Longitude).=20
Select the tab "Visible stars".=20
Press the "Calculate" button.

Now choose the stars in the spreadsheet or chart. To see = the name=20 of star in the chart, click the mouse over it. The name will = show in=20 a "hint label". Or select the star in the spreadsheet. A = circle will=20 show around the correspondent star in the chart.

If a printer is available, Navigator can print a = convenient sky=20 preparation (one page), with visible objects table and polar = chart.=20

Input tip: When=20 unsure about how to enter a value (date/time format, = number=20 format or number unit), place the mouse cursor over = the input=20 box. A hint will show with the field name, input = format and/or=20 example.

Taking=20 altitudes

back to the=20 top

Now lets take the actual measurements. Take the following = items=20 to the deck of the boat:
1) Sextant.
2) Watch.
3)=20 Pencil.
4) Paper with your sky preparation. Attach the = paper to a=20 board, so it's easy to take notes and your work will not be = carried=20 away by the wind.

Try to establish a routine to handle these items. You = will be=20 observing two numbers (altitude and time) at once, possibly = on a=20 rocking boat, so don't let these items make things difficult = in the=20 critical time. You might want to use preprinted tables to = organize=20 your data, like the one below. Save them as the = documentation of=20 your work.

Date:	twilight time:	assumed lat:	assumed lon:
index error:	watch error:	time zone:	Obs:
celestial=20 object	sky=20 preparation	observations	results
LOP	Name	Altitude	Az	Time	Hi =	Delta	Dir =	Az =
1
2
3
4
5
6
Astronomical position for ____ LOPs	Lat:	Lon:

-> = Click here to open this table in a new = window, to=20 print some copies =

When taking an observation, set your sextant = to the=20 expected altitude and point it to the expected azimuth (from = your=20 "preparation"), using a hand compass. The celestial body = will=20 probably show in your view.

Adjust the sextant to the correct instrumental = altitude. Write=20 name, time and altitude of the observed celestial object.=20
1. It's good practice to adjust the sextant micrometer = drum=20 always in the same direction. For example, put the star = below=20 the horizon and then bring it up by turning the drum in = the same=20 direction in all observations. If you go past, repeat = the=20 operation from the start. Do the same for the Index = Error=20 measurement. The sextant will give different readings, = depending=20 on the direction you adjust the drum. Using the same = direction=20 for both altitudes and index error measurements cancels = this=20 problem.=20
2. After adjusting the sextant's drum, read the watch = first,=20 because it's changing fast. Write the time. Then write = the=20 sextant altitude.

Before and after taking altitudes, = measure the=20 Index Error:

Set the altitude to 0=B000' and point to the horizon.=20
Adjust the drum until both sides of the horizon are = level.=20
Read the Index Error and write it.

Back to the navigation table, run Navigator.

Enter the index error.=20
Enter Height of the eye (Dip). In version 3.0+, you = can choose=20 the Dip units (meters, feet or minutes) .=20
Enter watch error, in seconds. See keeping=20 the time for more information on time keeping = methods.=20

Note on = the=20 index error: In versions prior to 2.5, the IE = was typed=20 with the plus signal when the index error was inside = the drum=20 scale. This number was then subtracted from sextant = reading by=20 the program.

Many users complained that this = input=20 convention was against the common practice in = celestial=20 navigation. They were used to work with the Index = Correction=20 (IC), with signal - when the IE was inside the = arc=20 scale.

After many messages, I agreed. = Starting with=20 version 2.5 and up, I changed this. So, if you are = upgrading,=20 make sure you use the correct input convention, as = illustrated=20 on the right.

Navigator 2.5 = and=20 up
Type = IC =3D=20 -2	type = IC =3D=20 +2

Old = versions=20 (navigator 2.0 and prior)
Type = +2	type=20 = -2

Clear all previous LOPs:

Select the tab "Astronomical Position".=20
Press the toilet button, to clear all LOPs.=20
Now select the "Line of Position" tab.=20
Set the assumed position (Latitude and Longitude). =

Now enter the measurements, one by one. For each = celestial=20 object, do:

Select the celestial object from the listbox.=20
Enter time of the observation.=20
1. You can use local time or GMT time edit boxes. In = this case,=20 automatic conversion to GMT is done.=20
2. If using local time, make sure the time zone and = watch error=20 edit boxes are correctly set.
Enter altitude of the celestial body.=20
Press the "Calculate" button.

The result will be something like this:

LOP for Sun
05/04/2001 13:43:54 GMT
Ass.Pos. Lat:23=B040.0'S  Lon:40=B030.0'W
Inst. Altitude: 56=B024.5'=20
Altitude of lower limb
Altitude corrections ------------
Par: 0.0'  Refr:-0.6'  SD:16.0'
Dip:-3.1'  IE:-2.0'
Total Altitude Correction:10.3'
Corrected Inst Altitude: 56=B034.8'=20
Object Positional data -----
LHA: 344=B048.9'=20
GHA: 25=B018.9'=20
Decl:  6=B013.8'N
LOP Results------------------
Calculated Altitude: 56=B037.8'=20
Intercept: -3.0 NM (away)
Az.calc:   28=B0

The two last lines have the results (Delta and Azimuth). =

If you feel the result is consistent with the expected , = press=20 the button "Save LOP". This will save this Line of Position = for the=20 calculation of the Astronomical Position (Fix), which will = be done=20 after you calculate all LOPs.

After calculating and saving all LOPs, go for the = astronomical=20 position calculation:

Select the tab "Astronomical Position". The LOPs you = have just=20 saved will be in the spreadsheet.=20
Press the "Calculate" button, to calculate the = astronomical=20 position. Your astronomical position will show. Please = note that,=20 in order to calculate the astronomical position, you have = to have=20 two or more LOPs. Having more lines is advisable, because = errors=20 in one observation will show more easily. A good number is = 4 LOPs.=20 Also, as we will see, sometimes we are going to discard = some of=20 them.

Refining = your=20 calculations

back to the=20 top

To achieve good results in celestial navigation, you need = to be=20 methodic. As you can see, there are many steps, and a = mistake in one=20 of them will only show in the end, if at all.

Enumerate the tasks you are doing - or are going to do - = and read=20 the measurements loud before taking note (navigators are = said to=20 speak to themselves). Make your notes in an organized table, = one row=20 for each celestial object. In the header of the table, write = date,=20 assumed position, time of twilight and index error. Have the = sky=20 preparation ready before going to the deck.

But even with all the care, some errors will eventually = show.=20 Wrong time or altitude (the so called 60 mile error). Bad = star=20 identification. Even wrong date. The important thing is to = detect=20 mistakes, and drop the LOPs with problem.

Having good dead reckoning navigation helps a lot. It's = also a=20 good idea to take a look in the chart showing the Lines of = Position.=20 If one of them seems out of the flock, you may deselect it = and=20 recalculate de position. This is why it's good to have more = lines.=20

Another problem is to have two or more LOPs that are = nearly=20 parallel. They will probably cross very far from the correct = position, even if they are close together. Navigator = accounts for=20 this situation by giving a small weight to crossings forming = small=20 angles. But it's better to deselect one of them and = recalculate the=20 position.

LOPs 3 and 4 nearly parallel. Select only one of = them.

In the figure above, we can see that LOP 3 and 4 are = nearly=20 parallel. Deselecting one of them would improve the = resulting=20 calculated astronomical position.

Observing the Sun

During the day, you can observe the Sun and the Moon. If = you can=20 see both at the same time, and they are in suitable = positions for=20 observation, you can calculate a fix, using the two lines of = position. The procedure is the same described above for = stars and=20 planets.

The only difference is that the Sun and Moon have = appreciable=20 diameters (about 32'). When measuring the altitude of Sun = and Moon,=20 align the lowest part of the body with the horizon. This is = known as=20 the lower limb. Navigator will correct for the semi-diameter = automatically.

Sextant image

You can also use the upper limb. In this case, uncheck = the "Use=20 lower limb" checkbox.

Running=20 fix

back to the=20 top

The altitude of the same celestial object in two = different times=20 may be used to find the position. For example, you can take = two=20 Lines of Position for the Sun, one in the morning and one in = the=20 afternoon. Because your boat is moving, you will have to = transport=20 the first line to the second line time. The position = obtained with=20 this method is called running fix.

Navigator (version 4.0 and up) can be set to transport = LOPs=20 automatically, when calculating the astronomical position. = This is=20 done by moving the assumed position. The LOPs chart shows = the=20 original LOP (blue) and the transported (red).

Take a look at the Auto Transport frame n the image = to the=20 left. This is where LOP transport is setup.

Choose one of the following transport modes.=20
- Don't transport=20
- To latest LOP time=20
- To LOPs mean time=20
- To Selected Time (i.e. specified in the top = time=20 frame)
Click 'Edit boat C&S' (course and speed) and = update=20 boat movement data.=20
Click 'Calculate' to calculate the astronomical=20 position.

Simple meridian passage = (noon sight)

back to the=20 top

When the Sun crosses our meridian, its azimuth is either = 0=B0 or=20 180=B0 (North or South). This means that a Line of Position = (LOP) for=20 the Sun, taken at this time, will have constant latitude. = This event=20 is called transit or meridian passage. For the Sun, it = happens=20 around local noon (+/- 20 minutes).

The navigator can take advantage of this event to check = the=20 latitude. The longitude can also be calculated, although = with=20 smaller precision.

This is what you must do:

Start taking observations of the Sun (time and = altitude) about=20 25 minutes before the expected transit time. In = Navigator,=20 select the Sun and use the command Object Data to = estimate=20 the transit time for the Sun in your assumed position. = Take a=20 couple altitude observations (p.e. 5 minutes apart) until = 15=20 minutes before transit.
At transit time, observe the highest altitude the Sun = reaches.=20 This is known as culmination altitude. It=B4s easy to = measure, since=20 the Sun will appear to hang with constant altitude while = passing=20 your meridian. After that, it will start to go down. =

Write the culmination (maximum) altitude. =
Keep checking the altitude until the Sun, now going = down, is=20 at the same altitude it was in one of the observations = made before=20 transit. The time of transit is the average of two times = with=20 equal altitudes (before and after transit).

For = example,=20 if you measured 61=B032' at 11:45:30 and 61=B032' at = 12:10:10, the=20 time of transit is (11:45:30+12:10:10)/2 or 11:57:50. The = altitude=20 value is the maximum altitude you observed (near transit = time).=20
Enter the transit time (the average you calculated) = and the=20 culmination altitude in Navigator. Select the tab=20 "Other calculations" and click the = "Simple Sun=20 Meridian Passage" button. Program will give your = position.=20

It's important to understand that the Latitude result is = related=20 to the maximum altitude the Sun reaches, and the Longitude = to the=20 exact time of the passage. So, the latitude can be safely = determined=20 even if you don=B4t have a reliable watch.

Better meridian passage=20 calculation=20

back to the=20 top

While the method just described is OK, is does not = account for=20 two factors: Sun declination change and boat position = change. These=20 two factors can affect the longitude result.

The Sun declination is always changing. It changes faster = on=20 equinoxes (spring and fall) and slower in solstices (summer = and=20 winter). So, the Sun 30 minutes after the passage is not in = the same=20 place (in the celestial sphere) as 30 minutes before the = passage.=20

The boat movement during this period can also be of = significance,=20 particularly if the boat is fast and is moving along the = meridian.=20

These two changes affect the actual meridian passage = time. In=20 this case, the average time between two equal altitude = observations=20 (before and after transit) is not the meridian passage time, = but=20 rather the culmination time. A correction must be applied to = find=20 the right passage time (and the Longitude).

To perform this calculation on the Navigator, select the = tab=20 "Other calculations" and click the "Sun = Meridian=20 Passage by Equal Altitudes" button. The form below will = show.

Enter maximum altitude (w/o corrections), IE, Dip, GMT = date, GMT=20 time of altitude 1 (before transit, w/o watch correction), = GMT time=20 of altitude 2 (after transit), watch error, boat speed, boat = course=20 and assumed position. The GMT times 1 and 2 are the ones of = equal=20 altitude observations (the actual value of the altitude is = not used=20 in the calculation, but remember to write it down, because = you will=20 have to use the sextant to measure the maximum altitude = between the=20 two observations).

The correction i is the difference, in seconds, = between=20 the culmination time and the transit time. It can be as much = as a=20 minute, or 15' in the longitude.

Please note that there are a couple conditions to = use this=20 method:

Sun altitude must be at least 65=B0.=20
The Sun's azimuth must be at least +/-20=B0 on equal = altitude=20 observations.=20
The equal altitude observations must be up to 40 = minutes -=20 before and after - transit time.

This method is particularly useful near the Equator.

Tip: If=20 there are clouds in the sky, it's recommended that you = take=20 several observations before transit. If you take only = one, the=20 Sun may become covered in the critical time after = transit. By=20 having many observations, you increase the chance of = having=20 one usable observation = pair.

Source: Navega=E7=E3o Astron=F4mica e = derrotas

Artificial = Horizon

back to the = top

If you live in a city far from the sea, you can't take = altitudes=20 of celestial bodies with a marine sextant, because you can't = see the=20 sea horizon. One way to work around this problem is to use = an=20 artificial horizon. The artificial horizon can easily = be made=20 with a plate filled with liquid. Water will do, but oil is = better.=20 The surface of a pool can also be used, if there is no wind = or waves=20 (the water surface must be completely flat).

To take the altitude with the artificial horizon, = point the=20 sextant towards the artificial horizon and make = reflected=20 image of the celestial body coincide with the direct = image.=20 The angle you read is twice the altitude of the body, = as=20 illustrated in the figure below.

Also read the index = error.

Navigator automatically corrects for the use of = artificial=20 horizons:

The program divides instrumental altitude by two. = Enter=20 sextant reading directly.=20
The Dip and semi-diameter corrections are set to zero. =
The index error is also divided by two.

Printing=20 Nautical Almanac Pages =

back to the = top

Navigator (registered version 2.5 or latter) has a = Nautical=20 Almanac page generator/printer. These pages are not exactly = the same=20 as real almanac pages, but they contain most of the = information=20 needed to do celestial calculations in the traditional way, = without=20 the computer.

Navigator generates the so-called "daily pages" (the ones = with=20 3-day celestial data for planets, stars, Sun, Aries and = Moon). The=20 yellow ("increments") pages are not generated because they = don't=20 change from year to year. You can use the yellow pages of an = old=20 almanac or do the interpolations with a pocket calculator. =

I choose to make the Navigator daily pages as similar as = possible=20 to actual almanac pages. But there are differences:

Did not include the latitude dependent tables = (Twilights,=20 Sunrise, Moonrise, Sunset, Moonset).=20
Did not include the Aries meridian passage time. This = number=20 is used to calculate the meridian passage of stars, and is = seldom=20 used.=20
Did not include the Sun's Equation of Time and = meridian=20 passage table. You may use an old almanac for the Sun's = meridian=20 passage calculations, as these tables are almost unchanged = from=20 year to year. Just use the table of the same day.=20
Did not include the Moon's meridian passage and age = table.=20
Did not include the planets' SHA and meridian passage = table.=20
Added three stars not included in most Nautical = Almanacs=20

I plan to include some of these numbers in future = versions.=20 Feedback from users about what features are most important = is=20 welcome.

If you compare the Navigator's almanac pages with = nautical=20 almanac pages, you will note small differences in the = numbers. These=20 are caused by different celestial calculation methods and = should not=20 be bigger than 0.5'. This error is small when compared with = other=20 imprecisions that affect celestial navigation, and will not = impact=20 your position significantly.

Printing the almanac pages

To print almanac daily pages, do:

Go to the celestial navigation window.=20
Select the "Other calculations" tab.=20
Press the "almanac pages" button. The "Almanac Pages" = window=20 will show.=20
Set the initial date for the 3-day page.=20
Select "Aries and planets" (left side page).=20
Press "Build page" and "Print".=20
Select "Sun, Moon and Stars" (right side page).=20
Press "Build page" and "Print".=20
Click in the "Arrow" button to advance 3 days and = repeat=20 operations from step 5). Proceed until you have printed = all the=20 pages for the desired period.

In order to print your almanac pages, you have to use a=20 non-proportional font (a font with fixed pitch). The default = font is=20 Courier New, size 7. Pages printed with this font will use a = single=20 sheet of paper (size A4). I know this is a small font, but = using a=20 larger one will result in two paper sheets for each page. = You may=20 experiment with other non-proportional fonts. True type = fonts are=20 better, because they can be resized to any small size.

Check the online web service, open to the public. Click = to v= isit=20 this service.

Chapter=20 2 - Star Finder

to table of=20 contents

Navigator Star = Finder=20 (version 3.0+) was completely redesigned. To = accommodate the=20 new set of features, this chart of the visible sky was = moved=20 to its own window (in previous versions, it was part = of the=20 celestial navigation window).

The new features = include:

Constellation=20 lines and names make it easy to identify = constellations and=20 celestial objects.=20
Ecliptic plot=20 shows the path of the Sun, Moon and planets.=20
Celestial=20 objects grid can be sorted by columns (ascending and = descending order) clicking the column header. =
The=20 spreadsheet now includes object magnitudes (note: = many=20 celestial objects have changing magnitudes. These = values are=20 fixed, to be used only as rough estimate).=20
Mouse cursor=20 shows altitude and declination when moving. When = pointing an=20 object, its name, altitude, azimuth, declination and = right=20 ascension are shown. Values cursor is transparent, = so you=20 don't loose the big picture.=20
Prints the=20 object list and chart. The printed chart uses the = printer=20 higher resolution.
Time = zone is=20 now imported from the operating system, accounting = for Day=20 Light Savings time.=20
Sky=20 background color indicates the light conditions = (day=3Dblue,=20 night=3Dblack and twilight=3Dnavy).
Windows=AE = Clipboard=20 support allows to cut-and-paste the chart to other=20 = applications.

Overhead view=20 option, so you can look up to the sky and the chart=20 simultaneously. In this representation, E and W are = flipped=20 and the chart is to be viewed upside down
(see = figure to=20 the left)

Options tab=20 allows easy and interactive chart setup (see figure = to the=20 left).
Boat = course=20 plot, to easy printed chart orientation.=20
Star finder chart and table now print in the = same sheet=20 of paper, much more convenient.

Using the Star Finder is easy:

Set your position (Lat/Lon)=20
Set the GMT date and time. If you opened the = star finder=20 by clicking the button in the celestial navigation = window,=20 these values are automatically set.=20
Set the boat course (optional)=20
Click the Calculate button

You can also animate the sky, specifying time = increments=20 and calculation frequency. This can produce very = interesting=20 animations, like how the sky changes from hour to = hour, day to=20 day and year to year.

And it can also be set to show the current=20 sky.

Chapter 3 - Chart=20 Navigation

to table of=20 contents

The Navigator chart module is relatively new = (started in=20 version 2.5), but has received important additions in = version 4.0.=20 It's now much more useful with the addition of raster chart=20 capabilities.

Instead of supporting the existing electronic chart = formats, I=20 choose to provide a set of tools to allow the user to import = existing paper chart images into the program. This 'do-it = yourself'=20 approach gives the user maximum flexibility.

All Navigator files are in text format and their=20 structures are easy to understand, to allow integration with = other=20 applications and Internet file sharing. The table below = enumerates=20 the Navigator data file types.

File extension	Description
.CHT	Navigator vector chart file
.NAV	Navigator desktop file
.CID	Navigator chart image description = (raster=20 image)

Vector = and raster=20 charts

back to the=20 top

The Navigator chart engine can show two kinds of = charts:=20 vector charts and raster charts.

Vector charts - In this type of chart, islands,=20 continents, routes and tracks are represented by polygons = and lines,=20 defined by a collection of points (Lat/Lon pairs). This kind = of=20 chart can be easily zoomed in and out, and is very fast to = render.=20 Navigator uses its own vector chart file format. No other = chart file=20 format is supported at this time. These files can be = produced, from=20 scanned charts, using the ChartMaker=20 program.

Raster charts - These charts are images (normally = scans of=20 paper charts). Navigator can use raster images in formats=20 JPG, GIF or BMP. These are popular file = formats=20 in the Internet, and many charts can be found for download = over the=20 Net.

All raster chart image files must first be imported - = using ChartMaker=20 program - before they can be used in the Navigator. = This step=20 is necessary to describe the chart image scale (i.e. how = pixels in=20 the image map to the real world).

Both vector and raster charts can be produced or imported = using=20 the ChartMaker=20 program, which is described in the next chapter.

Using = raster chart=20 images

back to the=20 top

In the image above you can see two raster chart images = visible in=20 a desktop, on a zoom animation. Before opening it in the=20 Navigator, a raster chart image it must be imported. = This is=20 done only once for each image, with the ChartMaker=20 program. The step creates a .CID file that is associated = with the=20 chart image (GIF or JPG). This file contains:

- Name of the associated image file (GIF, JPG or = BMP)
- File=20 description
- Reference points (which define how the = image pixels=20 map to the real world)
- Image MD5 digital signature (to = prevent=20 accidental changes in the chart image)
- Chart limits = (outside=20 rectangle)

Once the CID file is created, it can be added to a = desktop. Click=20 the chart image open button and select the CID file. Many = chart=20 images can be added to a given desktop. Images can be either = visible=20 or not. To play with chart visibility, use the small = checkbox in the=20 chart images listbox.

Tip: Since images are large in size, making = many=20 visible at the same time would consume a lot of = memory. Making=20 only the charts you need visible reduces the = amount of=20 memory used by the program. A memory of at least 32MB = is=20 recommended to use raster charts.

The image resampling process also consumes a lot of = CPU=20 power. To reduce the bumpy behavior while zooming or=20 scrolling, these calculations are implemented in = different=20 threads of program execution . That's why it takes = some time=20 for the raster charts to show after you zoom or=20 scroll.

You can also play with raster image = opacities,=20 making them partially transparent. This allows you to see = how two=20 charts overlap each other or compare them with the vector = chart=20 underneath.

Tip: Partially opaque (i.e. = transparent)=20 chart images consume CPU power - a 100% opaque chart = will=20 display a lot faster.

The chart images rendering order can also be changed, = using the=20 up and down arrow buttons in the right. The rendering order = is:

1- Background (sea color)
2- Vector chart = polygons
3-=20 Chart images (top-down order in the listbox)
4- Routes, = tracks=20 and marks

Tip: To transfer a CID file to = another=20 computer (or to share it over the Internet) , you also = need to=20 transfer the associated image file (GIF or JPG). Since = the CID=20 file contains the image file digital signature, there = is no=20 risk of accidentally changing the image while copying. =

Printing Chart=20 Images

back to the=20 top

Navigator Desktops containing raster chart = images can=20 be printed. You can use this to integrate different charts = together=20 in a single and compact printout. Quality is even better = than the=20 computer screen, because printers have a much higher pixel=20 resolution than monitors (monitors typically 75 DPI x = printers 300=20 or 600 DPI ).

This quality comes at a cost. = Ressampled chart=20 images may turn out big, requiring a lot of CPU cycles and = memory to=20 calculate. So be patient and make sure your computer has at = least=20 64MB of memory. If you have a laser printer, limit the print = resolution to 600 DPI. Don=B4t use 1200 DPI, because this = would result=20 in really big ressampled image and would probably hang your=20 computer.

I=B4m working to make sure that the printing = process is=20 smooth. You may find problems in extreme situations = (printing large=20 chart images with high resolution printers and little memory = available).

Partially opaque (transparent) images are = not=20 supported by printers. When printing, all chart images will = be=20 rendered opaque.

Chart = tools

back to the=20 top

The Navigator chart viewer has the following = tools:

Zoom tool=20

Zoom - Lets you zoom in and out the chart, = from the=20 whole world to a very small scale. To zoom in, press = the left=20 mouse button in the point you want to focus (screen = center).=20 To zoom out, use the right mouse button or click the = left=20 mouse button with Shift key pressed.

Measure - Click a = position and=20 drag the mouse. The caption will show two numbers: COG = and=20 Range.

COG is Course Over Ground. It's the = true=20 direction of the line. Range is the distance between = the end=20 points, in nautical miles.

Both COG and Range are calculated = using Lines of=20 Great Circle (LGC). This means that they are accurate, = even=20 for large distances.

Navigator's vector chart = interface=20

Route - This tool is = used to=20 draw routes. A route is a set of points in the surface = of the=20 earth, with optional associated text. Routes can have = any=20 number of points or waypoints. You can draw as many = routes as=20 you wish. Routes can be stored in Navigator Desktop = files=20 (.NAV files). You can make some routes invisible and=20 concentrate on your current route. You can also edit = routes,=20 change their colors and names.

At anytime you can check the COG and Range = between two=20 points of a route, and the total length of a route. To edit = a route,=20 click the checkbox "Edit routes/tracks". The route editor = will show.=20 You can change all attributes of a route (Color, Name, and = Visible).=20 You can also edit coordinates of points, by double-clicking = the=20 point in the spreadsheet. To add a point to an existing = route (or=20 track), click the route tool. In the menu, select Routes = Add=20 Point to route. Choose the route. Add one or more = points. Right=20 click to save points and end addition.

To create a new route, click the route tool = and click=20 the route points. Right click end route. When prompted, = enter route=20 name.

Tracks - This tool is used = to draw=20 tracks. Tracks are like routes, except that each track point = has an=20 associated date/time value. They are used to log the = positions on a=20 trip. Like routes, they can have any number of points. = Tracks can be=20 stored in Navigator Desktop files (.NAV files). You can make = tracks=20 invisible to concentrate on your current track. You can also = edit=20 tracks, change their colors and names.

To edit a track, click the checkbox "Edit=20 routes/tracks". The track editor will show. You can change = all=20 attributes of a route (Color, Name, and Visible). You can = edit point=20 data, by double-clicking the point in the spreadsheet.

To create a new track, select the track tool = and click=20 the first route point (left button). If you want, add more = points=20 with left clicks. When done adding points, right clicks the = chart.=20 Enter track name.

To add a point to an existing track, click = the route=20 tool. In the menu, select Tracks Add Point to route. Choose = the=20 track. Add one or more points. Right click to save points = and end=20 addition.

Marks- You can also add marks to the = desktop.=20 Select the mark tool and click one point, specify optional = text for=20 the mark and choose a mark icon.

Pointer- Use the pointer tool to = point chart=20 objects (islands, tracks, marks etc). If a name is = associated with=20 the object, a text will appear near the cursor.

Navigator=20 Desktop files

back to the=20 top

After loading a vector chart and/or raster charts; = changing=20 routes or tracks, you can save all to a desktop file. A=20 Navigator desktop file contains the state of the = chart=20 viewer, including:

- One Vector charts.
- Raster charts (i.e. chart = images)
-=20 Routes
- Tracks
- Marks

Desktop files have the extension .NAV, and are in text = format.=20

GPS=20 Interface

back to the = top

Navigator has GPS interface. This interface accepts NMEA=20 (National Marine Electronics Association) standard GPS = messages. Two=20 kinds of NMEA messages are accepted:

RMC - Transit Specific Navigation information=20 message- This is the recommended (default) accepted = message, because it has date and course information. RMC = messages=20 give Latitude, Longitude, date, time, course and speed.

GLL - Geographic Position Latitude/Longitude = message=20 - Select this one if your GPS does not support RMC=20 messages. GLL messages have only Latitude, Longitude and = time (no=20 date).

Note: The NMEA interface, available = in=20 most GPS devices, uses a RS422 hardware interface. = This is not=20 the same as the RS232c serial interface, available in = PCs.=20 While the 422 interface uses +12/-12V electric = signals, the=20 RS232 uses 0/5V. But since the PC uses the level of = about 3V=20 to distinguish between 0s and 1s, the connection works = fine in=20 most cases. However, they are different things, and = you may=20 experience problems connecting = them.

You will need a connection cable, which is = an optional=20 part for some GPS models. Check your GPS documentation for = more=20 details on activating the NMEA interface and selecting the = messages.=20 Some GPS devices disable the dataport, to save battery. You = probably=20 will have to change the default configuration to enable the = GPS data=20 output.

To open the GPS interface dialog click the GPS = Interface=20 button. A window will show, with current GPS position. = Clicking the Settings button will show the = GPS=20 settings page, as shown below. Clicking again hides = the=20 settings.

Set the baud rate to the same value as your GPS = device.=20 Most GPSs have a default baud rate of 4800.=20
Choose computer port number.=20
Click the "connected" checkbox to open the=20 communications port and start receiving GPS data. =

The upper panel will show the current position, = date/time=20 and position status (as reported by GPS device).=20

The GPS interface can be set to save a position = periodically=20 (AutoSave feature). Positions are saved to the current GPS = track. A=20 given desktop can have only one GPS Track. Use the "Choose = GPS=20 Track" button to choose the GPS track. If starting a new = travel, use=20 the "New track" button.

You can also save positions manually, by clicking the = "Save=20 position!" button. Just make sure the current position = status is=20 "valid".

Tip: If you use RMC=20 messages, Navigator will plot a small boat in the = current=20 position, pointing to the actual course. If you use = GLL, which=20 has no course information, a square will be=20 plotted.

Troubleshooting the GPS=20 connection

back to the = top

PC/GPS connections are sometimes tricky. A problem of = either PC=20 or GPS settings will unable the communication.

First, make sure that the GPS device is transmitting = data. Stop=20 the Navigator and open the Windows terminal (or = Hyperterminal in=20 Windows 95/98). Set terminal communications settings to 4800 = baud, 8=20 data bits, parity None, 1 stop bit. If the GPS device is set = correctly, you will see text messages coming from the GPS, = like=20 = these:

$GPRMC,001556,A,2332.648,S,04642.969,W,000.9,045.8,230997,=
018.5,W*6E
or=20
$GPGLL,2337.479,S,04718.352,W,235808,V*3

The first is a RMC message and the second a GLL. If you = don't see=20 any message, the GPS is probably not sending data. You may = have to=20 activate the GPS dataport and/or the transmission of each = message=20 type (Some GPS devices disable the data port every time they = are=20 turned off). After you start receiving one of these messages = (choose=20 RMC if available), return to the Navigator and make sure the = correct=20 data port, baud rate and NMEA message type are set. You may = set the=20 Navigator's GPS interface to beep on each incoming message. =

Leg=20 Calculator

back to the = top

When planning a route between two points far away (over = 1000 NM),=20 many issues must be carefully considered: sea currents, = prevailing=20 winds, ship routes, shallow and dangerous areas, foul = weather, etc.=20 While these points are very important, there are also = geometric=20 considerations: the Earth is a sphere and routes are not = straight=20 lines but arcs in the spherical surface. Two kinds of routes = are of=20 special interest: the lines of great circle = and the=20 rhumb lines.

A Line of great circle (LGC) is the = shortest=20 path between two Earth points. This kind of route is = contained in a=20 plane defined by three points: the two route end points and = the=20 center of the Earth. When plotted in a Mercator chart, a LCG = is=20 represented by a curve, and a straight line in Gnomonic = charts.=20 While LGCs are shortest, they have a few problems:

True course changes constantly from point to point.=20
Depending on the end points, a LGC can take you to = high=20 latitudes, which is sometimes undesirable.

Rhumb lines (RL) are routes with = constant true=20 course. They are represented by straight lines in Mercator = charts=20 and curves in Gnomonic charts (the opposite of LGCs). RLs = are easy=20 to navigate because the course is constant. They are, = however, a=20 little longer (the difference is larger in higher = latitudes).

Navigator Leg Calculator will = calculate=20 both LGC and RL routes between the two end points. To = open the=20 Leg Calculator, press the calculator button in the = toolbar or=20 choose 'Routes, Leg Calculator' in the menu.

Besides distance and course, Navigator shows the = difference=20 between the two options and builds routes with = specified=20 number of segments.

These routes can be inserted in the current = desktop. Routes=20 are added to the desktop with names "Rhumb Line" and = "Great=20 Circle". You may change these names in the route = editor.

In the picture to the left, the yellow line is the = RL route=20 and the red one is the LCG (both created with 22 = points). The=20 difference between the two is 41.8 NM (1.26%). The LGC = route=20 has a crosstrack difference of 241 NM to the RL route = (that=20 is, it goes up to 4=B0 south of the RL).

When building the routes, LGC route points are set = by the=20 program at constant longitude increments. RL route = points are=20 set at constant distance = increments.

Chapter 4- ChartMaker=20 program

to table of=20 contents

The ChartMaker program was designed to work with = chart=20 images in formats GIF, JPG and BMP, and prepare them for use = in the=20 Navigator chart viewer.

This program has two main functions:

Importing a raster chart images, producing CID files.=20
Making vector charts (i.e. digitalizing points and = polygons),=20 producing CHT files.

How = it=20 works

back to the = top

A computer image is formed by a large number colored dots = - also=20 known as pixels - disposed in a rectangular mesh. If the = image is=20 from a nautical chart or satellite photo, an algorithm can = be=20 designed to find the real world coordinates of any of these = pixels=20 and vice-versa. This is exactly how ChartMaker works.

The first step to make a vector chart or to import a = raster chart=20 image is to establish the scale model between the image and = the real=20 world. To do this, you have to click 3 reference = points and=20 enter their world coordinates (Lat/Lon pair). This is enough = to=20 define a scale between the real world and the image pixels. =

Technically, when you click the = three=20 reference points and enter the Earth coordinates, you = are=20 actually defining four vectors: two in screen = coordinates (S12=20 and S13) and two in Earth coordinates (E12 and E13). = Since=20 both geometries are similar, for any point P, we can = write:=20

SP =3D S1 + k * S12 + r * S13
EP =3D E1 = + k * E12 +=20 r * E13

(1)
(2)

where:
SP =3D Screen = coordinates of=20 point P
EP =3D Earth coordinates of point=20 P
S1 =3D Screen coordinates of reference = point=20 1
E1 =3D Earth coordinates of reference = point=20 1
r and k constants

From relation (1), we can calculate = constants=20 k and r. With these constants, we can calculate = the=20 earth coordinates of P from relation (2). This is how = the=20 program calculates the earth coordinates of any screen = point=20 (and screen coordinates of a Lat/Lon pair).=20

Mercator=20 Latitude scale correction

back to the = top

The method above works for linear latitude and longitude = scale=20 charts. But most navigation charts (and particularly the = detail=20 charts) are Mercator projections. Mercator projections have = a great=20 advantage: distances and courses between points can be = measured=20 directly from the chart. Angles are true, no correction is = needed.=20

As any coast navigator knows, distances in these = "regular" charts=20 must be measured in the latitude scale, one minute of = latitude being=20 one nautical mile. To allow this, the Mercator projection = latitude=20 scale is not linear.

If you look at the picture below, you will see that, as = latitudes=20 get higher, distance between parallels in Mercator charts = expands.=20 The size, measured in screen pixels, of a given latitude = minute is=20 proportional to 1/cos(Lat). For instance, when Lat=3D0, = cos(0)=3D1.0.=20 For Lat=3D60=B0, cos(60)=3D0.5, and so a minute of latitude = at this point=20 twice as large as at Lat=3D0. Of course this "latitude grow" = is=20 variable, and integral calculations are needed to calculate = the size=20 factor between two latitude intervals.

Navigator's screen chart representation is = not=20 a Mercator chart. The latitude scale is linear and = the=20 factor between latitude and longitude axis tick sizes = is equal=20 to Mercator projections in the center of the chart = window.=20 This is, however, of no consequence, since you are not = going=20 to "measure" anything on the screen. You will use = programs=20 calculators and measurement tools, which use the=20 mathematically perfect Lines of Great Circle (LGC) for = distance and course calculations.

Still, Navigator knows how to deal with = Mercator=20 chart images. When using a Mercator chart image on the = Navigator, remember to check the Mercator latitude = scale=20 checkbox. The program will correct for the = Mercator scale=20 automatically.

Which = chart=20 images can be used ?

back to the = top

Mercator chart images are OK, even if the image = is=20 rotated (like chart 1 on the left). It's difficult = to=20 perfectly align a large chart when scanning.=20 ChartMaker will rotate the chart in order to = align=20 its grid with the vertical direction (chart 2). This = is=20 necessary to speed up chart resampling, for = displaying.=20
Gnomonic and other curved grid projections = cannot be=20 used.
Some images (particularly satellite images) are = skewed.=20 Their constant latitude and constant longitude lines = are not=20 orthogonal (like chart 3 on the left). These images=20 cannot be used. After entering the three = reference=20 points, Chartmaker will inform you if this kind of = problem=20 is present.

Tips for=20 scanning charts

back to the = top

Scan using resolutions between 75 and 150 dpi. Avoid = large=20 files (over 1MB GIFs or JPGs). Images will have to be = ressampled=20 by the Navigator at run time while zooming. Large images = will=20 consume a lot of CPU cycles, resulting in poor and bumpy=20 performance.=20
When scanning large paper charts, you may detach the = page=20 scanner cover (if the scanner allows) to avoid folding the = chart.=20 Put some weight over the scanner cover, so that the paper = is flat=20 and perfectly in contact with scanner bed.=20
If the chart doesn't fit in the scanner bed, scan it = in parts,=20 overlapping between them. Then make a CID file for each = image.=20 Navigator can display different charts together, and will = even=20 allow partially opaque rendering, merging the overlaps.=20
Larger scanners (A3) are preferred, when available. A4 = scanners are small for large paper charts.=20
Hand scanners are not recommended, because they can = distort=20 the image scale. Use only page scanners.=20
Images should be saved in GIF or JPG format (JPG is = usually=20 better).

Choosing the=20 3 reference points

back to the = top

The 3 reference points indicate how the pixels in the = chart image=20 map to the actual world. Care must be taken in choosing = these=20 points, in order to achieve a precise scale. Below are some=20 guidelines for choosing the reference points:

bad = points- too=20 close!

Choose reference points that are as far from = each other=20 as possible. This will result in a more precise = scale. If=20 possible, choose points near the corners of the image. = In the=20 image on the left, points are too close and the scale = will be=20 poor.

bad = points- nearly=20 aligned! =

Reference points must not be aligned. In the = image=20 on the left, points are nearly aligned and the scale = will be=20 poor.

good = reference=20 points

In the image on the left, points are well = positioned (i.e.=20 far from each other and not aligned). Choose points = that are=20 close to the corners of the image, if possible.

If the chart has a grid, the grid line crossings = are=20 logical candidates for reference points (like point = 2). But=20 other points can be used and they don't need to define = a right=20 angle between them.

Importing a raster chart image

back to the = top

Open the chartmaker program and click Import = chart=20 image = and load=20 the image to be imported.=20
Check the Mercator scale checkbox, if chart is = a=20 Mercator projection (most are).=20
Take a good look in chart and choose the 3 = reference=20 points, as described above= .=20 Click each reference point with great care. Inform the = precise=20 latitude and longitude for the point.=20
Chartmaker will then calculate the scale and produce a = summary, rotating the image as needed (rotation is = considered=20 necessary if the angle between a meridian and the vertical = is=20 larger than 0.001 rad).=20
If the image was rotated by ChartMaker, you must save = it. I=20 use to save the image with a different name, keeping the = original=20 scan intact, but you may save with the same name, = ovewriting the=20 original.=20
If you made any mistake or if the image is unsuitable = for use,=20 the summary will inform you of this. You may try again, if = you=20 think the image is suitable and you made a mistake.=20
After the summary, you can click extra points in the = chart.=20 This is optional, but highly desirable, to further check = if any=20 error was done in the reference points.=20
If everything is OK, save the CID file (Chart = Image=20 Definition). This text file contains the information for = the=20 Navigator program to use the image: the reference points = data,=20 image file name and description.=20
The CID file also contains the image digital signature = (of=20 type MD5). This is to make sure that the associated image = is=20 unchanged. So, if you do any changes in the image - even = changing=20 a single pixel color, the CID file will become invalid. = This is a=20 security feature to avoid accidental image change. =

Making=20 vector charts

back to the = top

While raster charts are very complete, with the all = relevant=20 navigation information, vector charts cosume less memory, = are a lot=20 faster to draw and are "zoomable". This is why is = interesting to=20 have a vector chart to be loaded underneath the local raster = charts.=20

Navigator uses a custom chart file format, with = the CHT=20 extension. These are plain text ASCII files and can be = edited with=20 the Windows Notepad or Wordpad. Because providing detailed = vector=20 charts of all regions of the Earth is a demanding task, I = choose to=20 give users a tool to roll their own charts. Producing a = vector chart=20 means using a raster chart image to digitalize the points in = the=20 shoreline.

Chartmaker accepts three image formats: Windows BMP, GIF = and JPG.=20 If you are scanning paper charts, JPG is probably the best = format,=20 because files are smaller. It's a compressed format.

The CHT file

Once you have the image of the chart, load it in = Chartmaker. Now=20 you have to define the scale for this chart. Click and enter = the=20 Earth Coordinates for three distinct reference points = of the=20 image, as described above= .=20

Choose three points that are relatively distant to = each other=20 (at least 1/3 of the screen). Select points that form a = right=20 angle. Click the points and enter their Earth coordinates. =
After the third point, the caption will show the = coordinates=20 of the cursor, as you move the mouse. Check the = coordinates of=20 other points, to certify that your scale is accurate.=20
Select "Edit, Draw Axis" in the menu. The program will = draw=20 vertical and horizontal axis in 30' intervals. Check if = they are=20 the same as the image's axis. Draw again to erase the = axis.=20
Now draw the shoreline, clicking the points with the = mouse.=20 Draw different polygons to represent the islands and = continents.=20
After clicking all points of a given polygon, press = the "close=20 polygon" button. The last point will be connected to the = first.=20 All polygons must be closed.=20
Give a name for the polygon.=20
After drawing all the polygons, save the CHT = file.=20
Open it in Navigator chart viewer, to see the result. = Zoom in=20 and out, to check the details.

In the figure to the left, the 3 reference points = are=20 marked 1, 2 and 3. The coordinates are:

1) =
24=B000.0S 46=B025.0W=20
2) 23=B050.0S 46=B025.0W=20
3) 24=B000.0S 46=B006.6W

If you open the supplied=20 myworld.cht file in Navigator, you will see a=20 simplified chart of the whole world. I made it more = detailed=20 in one part (44=B000'W 23=B030'S), the region I = usually navigate.=20 You can do this for your region, by directly editing = the CHT=20 file with a text editor and adding the polygons of = your=20 region. This is a little tricky. You might prefer to = roll a=20 chart of your region only.

You may also merge CHT files, using an ASCII text editor = (like=20 the Notepad or Wordpad). Take a look in the CHT file header = for more=20 technical details on the CHT file format.

xxx