Re: How do I compute the longitude and latitude of a point at a certain distance?

There are a number of things that you need to be clear about to answer your question:

There are three directions commonly referred to as "North". Magnetic North, Geodetic North and Grid North. You need to be clear which one you are using
Presumably your starting point is a geodetic location (i.e. Lat/ Long) not a projected one (i.e. X/Y like UK National Grid or US State Plane)
What level of precision do you need?

Here are some hints:

Assuming a spherical earth makes calculations much simpler but less accurate
Things get more distorted near the poles, if you are only interested in locations below the artic circle you can simplify
Things get more distorted as distances increase, if you never want any distance more than 10km then simple geometry will probably be good enough

You can go all the way from doing a simple bit of trig (e.g. how long is 1 degree East-West, how long is 1 degree North-South and interpolate) to using a full blown coordinate conversion system. You have to decide how much error you are prepared to tolerate and how much time you want to invest.

A few months ago I looked into location conversion modules in CPAN and did not find any that met my needs.

Comment on Re: How do I compute the longitude and latitude of a point at a certain distance?

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Re: Re: How do I compute the longitude and latitude of a point at a certain distance? by BrowserUk (Patriarch) on Apr 22, 2003 at 11:15 UTC
All good points, especially the stuff regarding grids -v- geodetic locations and accuracy. However, it's worth pointing out that whilst 1 deg N-S stays constant (~70 miles), 1 deg E-W gets longer as you move from the equator towards the poles. 1 deg. longitude ~ 70 miles/111 km at the equator, but the same distance covers an arc of around 57 degs. when your at 89 degs. latitude (north or south). Hence the old conundrum of the bear walking South for 10 miles, then East for 10 miles then North for 10 miles and ending up back where he started. What color was the bear? Examine what is said, not who speaks. 1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. 2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible 3) Any sufficiently advanced technology is indistinguishable from magic. Arthur C. Clarke.	[reply]
Re: Re: Re: How do I compute the longitude and latitude of a point at a certain distance? by tachyon (Chancellor) on Apr 23, 2003 at 02:39 UTC
The bear of course was probably White. Additionally he was probably quite dizzy. `Diziness ~ 1/(10 - DPF) where DFP = Distance from pole.` [download] Further questions. Is there a finite or an infinite number of solutions to this problem? What are the possible values for DFP. If there is an infinite number of solutions what restriction(s) do you need to place on the problem to yeild a finite set such that there would be a sufficient population of bears to physically test the problem space say before the expiry of the Unix epoch? Assumptions such as the MPBPD (Mean Polar Bear Packing Density) and the MPBSL (Mean Polar Bear Step Length) will need to be made. Bonus marks for a regression analysis on...... cheers tachyon s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print	[reply] [d/l]
Re: Re: Re: Re: How do I compute the longitude and latitude of a point at a certain distance? by BrowserUk (Patriarch) on Apr 23, 2003 at 03:13 UTC
Is there a finite or an infinite number of solutions to this problem? Yes. What are the possible values for DFP. Depends on the size and extent of the floating icepack which in turn depends on the time of year. If there is an infinite number of solutions what restriction(s) do you need to place on the problem to yeild a finite set such that there would be a sufficient population of bears to physically test the problem space say before the expiry of the Unix epoch? A high tolorence to mindless experiments. Oh, and vegetarianism if I am to survive it:) Examine what is said, not who speaks. 1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. 2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible 3) Any sufficiently advanced technology is indistinguishable from magic. Arthur C. Clarke.	[reply]