railway design. The RGIS provide spatial informa-
tions from different sources. It can decide the accu-
racy location of railway line. The satellite images
can provide rich surface information of the earth.
The automatic new railway line selected system is
subprogram of the RGIS. It can select the railway
line on the screen of the computer to adopt the rail-
way line that closely follows. the profile of the
ground and to use construction materials that occur
near the railway line. This system can quickly find
all possible railway line direction. At that time, the
factors of influence every new railway direction
mainly is the topographic factors. The more smaller
the amount of fill earth and cut earth , the lower the
construction cost. The more shorter length of rail-
way line, the better transportation conditions. A
topographic map drawn on a scale of one to fifty
thousand, main national highways, rivers, artificial
buildings were entered by digitizer , using as a basic
map for railway line selecting. The contour topo-
graphic interval, Ah , is 10 m. In the railway de-
sign, the maximum slope rate in the mountainous
area is 12%. In the plain area the slope rate is 5%
or 39$. The smaller slope rate the better transporta-
tion condition. If we know the contoure topographic
interval 4^ , the maximum slope rate of railway
line s. Then it needs the horizontal distance on the
map is
Ah
Ad Ah Ll
S m
1
where x is the scale of the map. For example, in
the one to fifty thousand map, 4h = 10m, s =
12%
10 + 1000
Ah
din = == 12% - 50000 — 16: 7mm
+
m
If the 4d,, smaller or equeal than the Ad which is
the shortest horizontal distance between two ad ja-
cent contour line, i.e. Adj; X: Ad . The means the
terrain was flate, the railway line direction can use
free slope rate. At that given start point, the rail-
way line can choose in the straight line direction be-
tween the start point and terminate point. If
the Adi; > Ad , the means that the terrain is
mountainous area. The railway line have to use the
maximum slope rate. The railway line can not
choose in the straight line direction between the
start point and the terminate point. Then the given
start point as a circle center, the 4d, as a radius,
drawing a circle intersect a point of the next coun-
tour line, linking the two points of start point and
the newset point, get a straight line. The slope rate
of the straight line is 12% along the topographic
surface. This means that, a railway line on this
straight line direction, the railway line are not need
fill earth and cut earth. The constructure cost are
the lowest.
Then, with the newly set point as the start point
the Ad;; as a radius, to make a similar search a-
gain. Then, the optimum direstion is decided, and
the start point is moved in that direction. Thus,
this operation is repeated till the terminate point is
reached. Along the optimum direction, matching
suitable straight line and curve line, get a optimum
new railway line.
In practice, from the start point, the 4d,, as a ra-
dius may intersecte two points on the next countour
line. One point is the correct direction along the
straight line between the start point and the termi-
nate point. Other point may be in a different direc-
tion leading the railway line in to a Wrong direction
(see Fig. 1). Thus, the computer have to decide
which direction is correct direction. Using a given
algorithem , two angle 7, (between line at and ab, ),
7, (between line at and ab, ) are computed, com-
pared the 7, and 7, , choosing the line of smallest
angle 7, is the optimum direction.
Figure 1. Search Direction
3. The Optimum Transportation Path
Selected System :
The Railway Transportation Information System
(RTMIS) is the main part of the RGIS. It connects
with more than six thousand railway stations dis-
979
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
