Help me to convert X,Y to Latitude Longitude on mouse click.

Hi all,
i have a problem in converting X,Y to Lat Long in the following
condition.
I've been given 2 points with coordinates and .
Now while mapping the rectangular area covered by these 2 points on to
the computer screen, how do i calculate the exact kilometer/miles value
between those points corresponding to the pixels value at the point of
my mouse click, considering the spherical nature of the earth's
surface.

i know the formulae to convert Lat long to Kms which is given below.
d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos(lon1-lon2))
using this formulae i can find the distance between the pts and
linearly map the Kms/miles on the rectangular area covered by the 2 pts
and find the lat long. but this is not accurate because of the
spherical nature of the earth. can anyone plz help me to do the same
accurately.
Thanks,
Su

Help me to convert X,Y to Latitude Longitude on mouse click.

sunita.svr@gmail.com wrote:

Most navigation programs such as Oziexplorer will do this for you, thus
saving a laborious trig calculation. Also your Gps, if a mapping GPS, should
be able to do it.

sunita....@gmail.com wrote:


Are you trying to convert a mouse click to latitude/longitude,
or are you trying to determine distance between two known
latitude/longitude points?

To do the former, you need to know your map scale, and
the latitude and longitude of some reference point whose pixel
value you also know.

pixels, map height in km / image height in pixels. Do the same
thing for width, but scale by cos(latitude) to allow for parallels
of longitude getting closer together. Now you know how many
meters each pixel is, and can relate pixel coordinates and
distances to your known point. Turn them in to latitude and
longitude if you need to: one minute of latitude is 1 nautical mile,
which is 1.852 kilometers.

Unless you are measuring more than tens of kilometers
in your maps, a flat Earth Pythagorean approximation
will give you all the accuracy you need. Just remember
to scale the longitude delta by cos(latitude).

One project I'm involved with uses a flat approximation
to 50 km, a spherical approximation to 1000 km, then
a WGS 84 oblate spheroid calculation above that...

Laura Halliday VE7LDH "That's a totally illegal,
Grid: CN89mg madcap scheme. I like it!"
ICBM: 49 16.05 N 122 56.92 W - H. Pearce

thanks for the reply,

what u have told is what i m doing right now. my problem was actually
in getting the exact map scale..
can u plz tell me that if i m given (lat, long) of one point (say
point1) and distance (say D) in Kms/miles then how do i find the lat
long of the other point D Kms from point1.

sunita....@gmail.com wrote:


There are infinitely many "other points" (around a circle) at a
given distance from the first point. Your question has no unique
answer.

At the risk of sounding stuffy and old-fashioned, it would be a
lot easier to read your messages (and maybe figure out just
what it is you're asking) if they were in something resembling
standard English.

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte