Geoscience Reference
In-Depth Information
2. While mapping in projection zone boundaries, the control points in adjacent
zones are usually needed, which should be transformed into the same zone
accordingly.
3. Zones 3
wide are needed for large-scale mapping (1:10,000 or larger-scale).
However, the national control points usually only have the coordinates of the 6
zones. Hence, a transformation is also needed between the 6
zones and the 3
zones.
After deriving the formulae for direct and inverse solutions of the Gauss
projection, transformation between adjacent zones will be easy. First, we compute
the geodetic coordinates (L, B) of a point given the Gauss plane coordinates (x, y)of
this point in zone I according to the formula for inverse solution of the Gauss
projection. Then, we compute the Gauss plane coordinates (x, y)
II
of this point in
zone II based on the longitude of the central meridian (L
0
)
II
in this zone according to
the formula for direct solution of Gauss projection. The process can be expressed
as:
L
ð
I
inverse solution of the Gauss
projection
L
ð
II
direct solution of the Gauss
projection
ð
I
x
;
y
!
ð
L
;
B
Þ !
ð
II
x
;
y
Coordinate Transformation Between Zones with 3
Width and Zones
with 6
Width
We know that the central meridian of 3
zones, in even-numbered zones, coincide
with central meridian of the zones 6
wide, and in odd-numbered zones coincide
with the zone-dividing meridian of the 6
zones. Hence, the coordinate transfor-
mation between the zones 3
and 6
wide has also to be considered in two different
situations.
When the Central Meridian of the 3
Zone Coincides With That
of the 6
Zone
In Fig.
6.10
, the central meridian of the 3
zone 41 and that of the 6
zone
21 coincide, for both of which the longitude 123
∘
is chosen as the central meridian.
The difference between central meridians causes the coordinate system in each
projection zone to be different. If the central meridians in the projection zones are
coincident, then their coordinate systems will be the same. Given the coordinates of
point P
1
in the 3
zone 41 to compute its coordinates in the 6
zone 21, no
transformation is needed and vice versa.
Search WWH ::
Custom Search