[Date Index]
[Thread Index]
[Author Index]
HELP!! 3D > 2D math problems..
 To: mathgroup at smc.vnet.net
 Subject: [mg24399] HELP!! 3D > 2D math problems..
 From: * <keen at ulster.net>
 Date: Wed, 12 Jul 2000 23:13:42 0400 (EDT)
 Sender: ownerwrimathgroup at wolfram.com
hello!! i'm having a little problem with what i guess would be spherical
trig..
i divided the Earth into 12 identical pentagons  3 at each pole and 6
around the equator.. using Lightwave i rendered an image of each of the
pentagons face on.. i know the coordinates, in latitude and longitude,
of each point of each pentagon.. so given the coordinates of a location
somewhere on the globe  NYC (40N42, 74W00) for example  i can tell
which pentagon it's in.. my problem is plotting an accurate
representation of the location on the rendered image.. i was given very
helpful math on how to convert 3D coordinates to 2D which i translated
(roughly) into this code:
         
loc = location coord
centre = pentagon centre coord
sloc = loc  centre  subtract centre from loc coord to make it
relative to the centre of the pentagon
theta = (PI * sloc.horz) / 180  convert coord to radians..
phi = (PI * sloc.vert) / 180
r = 3.5530  radius of the sphere in Lightwave
x = r * sin(theta) * cos(phi)
y = r * sin(phi)
z = r * cos(theta) * cos(phi)
f = .4696  focal length in Lightwave
d = 6.3682  the distance between the centre of the sphere and the
viewer in Lightwave
sx = (f * x) / (d  z)  2D coords of the loc..
sy = (f * y) / (d  z)
         
the problem i am encountering now is that this doesn't account for the
way latitude curves around the globe  this is especially noticable
around the poles where it would be most severe.. it is treating all
locations as if the pentagon is centred on the equator and prime
meridian.. does this make sense?? any help to get this routine to work
would be greatly appreciated.. thanks!!
y'r pal kK
Prev by Date:
subscripted variables and comments
Next by Date:
Re: l'Hopital's Rule
Previous by thread:
Re: subscripted variables and comments
Next by thread:
Modifying illumination shades
