hi all,

iam facing a problem regarding the realtion between latitude,longitude
and (x,y) pixcel.The basic idea is to plot the tracks given by gps
reading ,to the map .
But i just cant figure out how each latitude can be plotted?i hve been
struggling for past 6 months,but cldnt find a solution...and my project
deadline is juat around the corner..so please do help,


regards,
dips

i hve been
struggling for past 6 months,but cldnt find a solution...and my project
deadline is juat around the corner..so please do help,

Your request doesn't have enough information for anyone to give you specific
advice, but you can go to the Maptech mapserver site and find your gps lat
and long on their maps. The maps have a box next to them that display the
lat and long as you move the cursor over the maps. There are several
different location output formats available:

http://mapserver.maptech.com/homepag...TOKEN=62496677

If you and looking for a program that will output a plotted map from lat and
long info that you input, then perhaps someone can point you in the right
direction.

Your question seems somewhat unclear.

(BTW, a nautical "map" is properly called a "chart").

To plot latitude and longitude, you will need a chart (or a map) with
scales and reference points for latitude and longitude. A pair of
dividers (geometry compass will substitute), will be essential, along
with a straight edge and a pencil.

Latitude and longitude are expressed in degrees, minutes, and seconds.

Lines of latitude run parallel to the equator. (think of them like
rungs on a "latter"). Lines of longitude run betwen the north and south
poles. (it's cold at the poles, so you need your "long" underwear)

In a practical application: let's say you wanted to plot the
coordinates 47.31.1N and 122.28.5W. You could do that by using chart
#18448, but taking the same steps would help you find a different plot
on any chart where different coordinates would appear.

To start, you need to establish either your latitude or your longitude.
Some purist might insist that it's important to start with one position
or the other, but I usually start with latitude.

On chart 18448, there's a line of latitude marked at 47 degrees, 30
minutes. Since we're looking for 47.31.1, that line is a good place to
start. On the left edge of the chart is a scale to use when calculating
latitude. Take the dividers, (or the geometry compass), and spread the
legs until one is on the 47.30 mark and the other is
11 little tick marks to the north. The first ten tick marks
bring yhou to 47.31N, and the 11th brings you to 47.31.1N

(incidentally) that minute of latitude between 47.30N and 47.31N equals
a nautical mile.

That spacing on the dividers can now be used to establish 47.31.1
anywhere across the chart, simply put the "bottom" leg on 47.30 and the
more northerly leg will be on 47.31.1N (as long as it is at right
angles to the line)

At this point you could mark any two points that are 47.31.1N on the
chart and draw a line between them. Somewhere on that line, or on its
extension beyond the reference points, is where you are in relationship
to the equator. To find out where you are on the globe, you need to
find the single point on that line that represents your position.

At the top of the chart is a scale that represents longitude. In this
example, we are looking for 122.28.5W

On chart 18448, there is a vertical reference line for 122 degrees, 30
minutes W. Using the dividers again, measure toward the prime meridian
in Greenwich Englan (to the east) 11 and 1/2 tick marks. We measure
east because we are looking for a longitude with a lower number than
the reference line, and we'd measure west if we wanted a longitude with
a higher number, (for example, 122.31 would be left, or west, of
122.30).

The dividers will now indicate 122.28.5W anywhere on the chart as long
as one leg is resting on the reference line and the other leg is at
right angles to the line.

When you find the point where the line of your longitudinal position in
relationship to the prime meridian intersects the line of your lateral
positional in relationship to the equator, you will know just exactly
where you are on the chart and will have "plotted" your position. (In
this case, you would be just off of Pt. Vashon, at the north end of
Colvos Passage, in Puget Sound.)

If that doesn't help, or answer your question, please try restating the
problem you are experiencing.

On 15 Feb 2005 21:58:11 -0800, "dips"
wrote:

hi all,

iam facing a problem regarding the realtion between latitude,longitude
and (x,y) pixcel.The basic idea is to plot the tracks given by gps
reading ,to the map .
But i just cant figure out how each latitude can be plotted?i hve been
struggling for past 6 months,but cldnt find a solution...and my project
deadline is juat around the corner..so please do help,

Are you trying to pull data from a gsa directly to a plotter?

A little more information would be helpful.

Later,

Tom

dips wrote:
hi all,

iam facing a problem regarding the realtion between latitude,longitude
and (x,y) pixcel.The basic idea is to plot the tracks given by gps
reading ,to the map .

The "realtion" (=relation??) between lat & long constantly changes as
you move away from the equator.

Navigation is not done "on" a chart (it's extremely difficult to be
accurate with pencils, instruments etc on a chart, even more so on a
small boat:-)) but traditionally it's done via math calculations, then
the results are "plotted" to a chart, hence an electronic chart plotter
is programmed to calculate the answers very quickly & display the
plotted track.

1 minute of latitude is 1 nautical mile in length on the face of the
earth; anywhere on earth, but

1 minute of longitude is ONLY 1 nautical mile in length at the equator.

Going north or south of the equator, the length of a minute of
longitude gets shorter the further you move away from the equator, till
at the poles it's length is nil.

Basically everything can be reduced to right angled triangles (they're
spherical triangles). After that there are several simple formulae (many
others do the same thing) which given some "knowns" you can work out the
"unknowns"

So plotting a track onto a chart from various knowns is just a matter
of applying the required formula from what you do know.

Some of the most commonly used formulae a-)

Difference in latitude
Distance = ------------------------
COS of the course

or the same thing is

Distance = difference in latitude X SECANT of the course.

Difference in longitude X COS of the mean latitude
Tan course = ---------------------------------------------------
difference in latitude.

Difference in lat. = distance X COS of the course.

Difference in long.= distance X SIN course X SECANT mean lat.

or

distance X SIN course
Difference in long = ------------------------
COS mean lat.


So once you have a chip programmed with the right formulae, then as the
GPS delivers the actual positions, the plotter can calculate & place the
track on the screen, or if you want to manually draw it to a chart then
you can calculate the lat & long with your "knowns" & just join the dots.

K

& the Krause lie of the day???

Not only does this delusional liar see himself as a "real" boat owner;
he also makes up lies about every facet of boating including always
buying below the market & yes you guessed it, our lying Krause always
claims he sells (just before anyone actually checks) well above it,
indeed he says he operates in his socialist union fantasy where
"markets" don't even exist:-)


The Hatteras is sold. The SeaPro is loosely for sale against a guaranteed
trade-in value good through 30 June towards a new boat. I'm not
concerned with
the "next" issue and I never have been. I've bought and sold upwards of
25-30
boats over the years without ever once "consulting" any of the guides.
Time and
again, I've had surveyors tell me, "Wow...this boat shows way off the
top of the
bluebook allowances..."


No but seriously:-) if he let go of it he'd just fly away; yes????

"dips" wrote in message
oups.com...
hi all,

iam facing a problem regarding the realtion between latitude,longitude
and (x,y) pixcel.The basic idea is to plot the tracks given by gps
reading ,to the map .
But i just cant figure out how each latitude can be plotted?i hve been
struggling for past 6 months,but cldnt find a solution...and my
project
deadline is juat around the corner..so please do help,


regards,
dips

A simple matter of mapping the spherical coordinates to cartesian
coordinates according to the rules of some projection, see for example
Mercator. There are others. Which did you intend to use?