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

in reply to How do I compute the longitude and latitude of a point at a certain distance?

if you want rough answer not taking into account non-spherosity of the planet on the large scale nor the curvature of the planet on the small scale i would think something like this might be close enough.

break your distance into EW and NS components.
find circumference of planetoid. --> c
your loc = x,y (longitude,latitude)
find circumference at original latitude. --> c' = c * cos(y); (c' = c at equator; c' = 0 at 90deg)
x' = x +- ( c' / 360 ) * EW
y' = y +- ( c / 360 ) * NS

be carefull near the poles!

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

Replies are listed 'Best First'.
Re: Re: How do I compute the longitude and latitude of a point at a certain distance? by Bilbo (Pilgrim) on Apr 22, 2003 at 08:32 UTC
I think that this is almost right, but not quite. c/360 gives the distance north-south per degree, whereas what we actually want is degrees per unit distance NS, ie 360/c. Similarly for the distance EW. We want the final result to have dimensions of an angle but the equations that you give have inconsistent dimensions (angle + distance^2/angle). The two equations should be: x' = x +- ( 360 / c' ) * EW y' = y +- ( 360 / c ) * NS The mean radius of the earth is 6371 km (NASA), so c = 40030 km.	[reply]
Re: Re: Re: How do I compute the longitude and latitude of a point at a certain distance? by zengargoyle (Deacon) on Apr 22, 2003 at 09:06 UTC
you are so correct! i should have made a units thingy. `360 deg \| EW m 360*EW deg ---------\|------- = ---------- c' m \| 1 c'` <	[reply]

In Section Seekers of Perl Wisdom