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A question about the lat/long coordinates system (Read 404 times)

Jul 15^th, 2004 at 12:22am

Auriga Offline
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FS2002 gives coordinate info in deg, min, sec format. I found a calculator program on the internet that converts into decimal format (I need decimal format so that can do calculations more easily). How do these values (in decimal format) translate into meters or feet?

Here is an example of two points (in decimal format) that I need to know the distance between:
Point 1: Long -87.831505, Lat 42.984665
Point 2: Long -87.83128045, Lat 42.98464722

Now, the difference between the two longitude points is 0.00022455. How do I figure out how this translates into feet (or fraction thereof)? The distances I'm trying to calculate are quite small so I don't need to account for the curving of the earth....I'll just assume a flat plane. I am hoping that it is not necessary to apply Great Circle formulas.

I tried converting things and applying different formulas but I only ended up confusing myself. I think there must be something I'm missing. One minute of lat/long = I nautical mile. That ‘second’ is in base 6 (I think??), so how does the decimal (base 10) translation of that one second convert into nautical miles. Then, how do nautical miles convert into feet?

I need the simplest way to do the conversion and in a form that I can put in an Excel spreadsheet.

Thanks, Christine

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Reply #1 - Jul 20^th, 2004 at 3:48am

Poseidon Offline
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Well, basically I think it is more straight forward if you use the deg-min-sec rule as 1 min = 1 mile.
However your question about a formula is an interesting one. I will try to define one (when I have some free time) and I will come back on the subject.

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Reply #2 - Jul 20^th, 2004 at 4:28am

Hagar Offline
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Hi Christine. I'm not sure what you're using this for. Here's the basic formula. http://geography.about.com/library/howto/htdegrees.htm
This is the easy way. http://www.unn.ac.uk/~evgp1/gary/dec2deg.htm

Some of the older FS utilities worked in decimal fractions of minutes rather than seconds. There's a CFG tweak for the early M$ sims like CFS1 to change the onscreen text to display in degrees, minutes and fractional minutes.
DISPLAY_FRACTIONAL_MINUTES = 1
I haven't tried it in FS2002 & this might just confuse the issue.

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Reply #3 - Jul 23^rd, 2004 at 4:45pm

ziliu Offline
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First I must say I'm new here. Hello everybody!

About the lat/long-system. I don't find it hard to do calculations in sexagesimal, it is just like the hour-minute-second system of time. I have never heard a friend say: Let's meet in 1.25 hours, ok? And for more complex calculations, most scientific calculators have the option of inputting value in sexagesimal. I just had to say this. Do whatever you feel is comfortable.

And then how latitudes and longitudes convert into miles and feet and metres and so on. Many here have stated I minute (= 1/60 degree) equals one nautical mile. This is not exactly true. Yes, one minute of latitude equals one nautical mile on the earths surface. But how longitudes convert into miles is dependent on what latitude we are at. One minute of longitude is only one nautical mile when the latitude is 0 degrees, i.e. when you're on the equator. Otherwise the formula would be that one minute longitude = cos(latitude) nautical miles.
cos is an abbreviation for cosine, and is a trigonometric function. I rarely use excel myself, but I bet there has to be a cos function or something equivalent.

And I have no idea how many feet there are i a nautical mile, but that shouldn't be to hard to find out. somewhere around 5000 I think.

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Reply #4 - Jul 23^rd, 2004 at 7:25pm

Poseidon Offline
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Quote:

One minute of longitude is only one nautical mile when the latitude is 0 degrees, i.e. when you're on the equator.

You are right as it concerns real world but not in FS where the world is not even a sphere but a cylinder instead. Moreover the 1 minute= 1 mile although not exactly correct (in real world) still can be used as a draft rule of thumb.

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Reply #5 - Jul 24^th, 2004 at 3:15pm