At 8:31 AM -0700 9/11/08, mike wrote:
On Thu, Sep 11, 2008 at 8:17 AM, tedd <tedd.sperling@xxxxxxxxx> wrote:
Considering that my other profession is Geophysicist, I'm kind of up on
those sort of things. The Earth is an oblate spheroid and the computation to
include the curvature of the earth would be a bit more involved.
what do you think of the code i mentioned earlier?
$distance = number_format(ceil(69*rad2deg(acos(sin(deg2rad($ulat)) *
sin(deg2rad($vlat)) + cos(deg2rad($ulat)) * cos(deg2rad($vlat)) *
cos(deg2rad($ulong - $vlong))))));
where:
$ulat = latitude of user #1
$ulong = longitude of user #1
$vlat = latitude of user #2
$vlong = longitude of user #2
I took the very popular mysql query (at the time) that supposedly
works with a sphere and mapped it to php functions and it has appeared
to work very well. I have only tested with US zip codes, but the
concept should be the same as long as lat/long are centered properly.
I dunno.
But I do know that knowing the latitude and longitude of two points
on the surface of the Earth and then trying to calculate the actual
distance between each is not a trivial task
Take a look at:
http://en.wikipedia.org/wiki/Latitude#Degree_length
In that table you can see that for every degree north-south there is
a change -- likewise, for every degree east-west AND those changes
are not equal.
This has been a problem for map makers for a long time.
I remember surveying ancient playas (i.e., lake-beds) in the Mohave
desert where my rod man would travel away and I would see his boots
disappear beneath the curvature of the Earth. Now, what's the
distance between me and my rod man? Is it the distance I see in my
survey instrument or the distance of my rod chain? One is a straight
line while the other isn't -- which is the correct one?
Cheers,
tedd
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