2. Navigation
is not about you, or your mind, or what you
can do. It's not about the sun and stars.
It's really about Everything.
-- Shorty Bertelmann, Navigator
32. ## Position Fix :
in plane geometry (I)
Situation:
1. You do not know where you are.
2. All you know is the positions
of A and D , their altitudes
(60o,45o), and length of AB and
DE
How to solve your position ?
D
A
E
B
1
√3
33. ## Position Fix :
in plane geometry (I)
Solution:
1.
for A, altitude = 60, RA=1
for D, altitude = 45, RD=1
2.
plot the circles with radius = RA
and RD.
3.
C must lie on the intersections.
A
√3
34. ## Position Fix :
in plane geometry (I)
Solution:
1.
for A, altitude = 60, RA=1
for D, altitude = 45, RD=1
2.
plot the circles with radius = RA
and RD.
3.
C must lie on the intersections.
A
B
D
E
45
45
45
60
60
60
C
C
1
√3
35. ## Position Fix :
in spherical geometry (I)
Where H1 > Hc > H2
Geometric Position
天體於地球之投影位置
Circle of equal Altitude
等高度圈
Pn
Assumed Position
假定船位
36. ## Position fix :
in spherical geometry (I)
What is the length between AP and GP?
1) the angle of XZ = zenith dis.
2) 1 nautical mile = 1 海浬
(on earth) =1’arc
= 1/60° arc
≒ 1852 km
Problem of High Altitude Method (高高
度觀測法)
1) radius too large
2) distortion on sea chart
AP
39. A =當地時角(LHA)
B= 天體角
C =方位角(Az)
Terrestrial Triangle
a = 90 - Hc
b= 90 -L
c =90 -Dec
sin(Hc) =sin(L)sin(Dec)+cos(L)cos(Dec)cos(LHA)
sin(C) =cos (Dec)sin(LHA)/ sin(Hc)
@ Northern Hemisphere
North Pole
GP
AP
## Position fix :
in spherical geometry (II)
51. Warm up
1990年6月5日，某船2000 DR L41°34.8’N,
λ17°10.5W，於ZT 20-01-56，以船用六分儀觀
測Pollux，得H028°02.1’。試以航海曆及229
表，求AP、a及Zn。
( key: GP,LHA,AP )
Zone time ( ZT ) 20-01-56
Zone difference ( ZD) +1
_________________________________________________
Greenwich mean time (GMT) 21-01-56
52. Warm up
1990年6月5日，某船2000 DR L41°34.8’N,
λ17°10.5W，於ZT 20-01-56，以船用六分儀觀
測Pollux，得H028°02.1’。試以航海曆及229
表，求AP、a及Zn。
( key: GP,LHA,AP )
Greenwich mean time (GMT) = 21-01-56
GHA ♈ 209°01.5’
SHA ( Pollux ) 243°49.1
____________________________________________________
GHA ( Pollux ) 452°50.6’
=93°19.7’
