Analytical method for GIS basic data acquisition
According to the ground control points read out fro, old maps, and the related image coordinates measured on analytical plotter, the exterior orientation elements can be obtained using the phogrammetric method of space resection. In order to overcome the strong correlation among exterion orientation elements of SPOT images, the repeated iteration method is adopted to calculate the linear elements and angular elements separately. The formula for solving exterior orientation elements come from collinearity equation of SPOT image. The first step is to solve linear elements by the use of following error equations.
Vx
i=a
14DXs
0 + a
15DYs
0 + a
16DZs
0 + a
14y
iDk
4 + a
15y
iDk
5 + a
16y
iDk
6-Ix
i
Vy
i=a
24DXs
0 + a
25DYs
0 + a
26DZs
0 + a
24y
iDk
4 + a
25y
iDk
5 + a
26y
iDk
6-Iy
i
Then, the second steps is to solve angular elements according to the following error equations :
Vx
i = a
11Dj0 + a
12Dw0 + a
13Dk
0 + a
11y
iDk
1 + a
12y
iDk
2 + a
13y
iDk
3 - Ix
i
Vx
i = a
21Dj0 + a
22Dw0 + a
23Dk
0 + a
21y
iDk
1 + a
22y
iDk
2 + a
23y
iDk
3 - Iy
i
Where
a
11 = -(x
2cos
k/f + f* cos
k)cos
w
a
12 = -(f + x
2f
-1)sin
kcos
f0
a
13 = 0
a
14 = (a
1f + a
3x)/Z
a
15 = (b
1f + b
3x)/Z
a
16 = (c
1f + c
3x)/Z
a
21 = -x sin
w + f sin
kcos
w
a
22 = -f cos
k
a
23 = -x
a
24=a
2f/Z
a
25=b
2f/Z
a
26=c
2f/Z
in which
Z=a3(x1-Xs1) + b3 (y1-Ys1) c3(Z1-Zs1)
Above procedures are iteratire
After the exterior orientation elements are obtained, we transform them and their change rates into the model coordinate system of analytical plotter. The transformed values can be used directly as the orientation parameters for the plotting of SPOT image on analytical plotter.
The plotting software system of spot imagery
The system program and the service program of analytical plotter are developed based on the photgrammetric frame central projection. In the real time circulation program, (Loop program) of the system, the image point and the object point are corresponded each other according to the well known collineraity equation. Because the SPOT image is composed of 6000 lines linear central projection image instead of place central projection, the normal Loop program, cannot be directly used. To solve this problem, the line-sean geometry of SPOT imagery must be considered and the exterior orientation elements of SPOT image should be line by line changed in real time in order to meet the need of corresponding relation of image point with object point I original Loop program, but actually, this not possible or it is very difficult to realize such change. To solve this problem, a modified method using stereo correction grid is suggested Konecny.
According to his thought, the original Loop program is interpolated with a real time grid correction program, which is executed co-ornately with original Loop program. When the measuring mark is moving according to the principle of central projection, an additional movement is taken in order to satisfy the projection principle of central projection principle of SPOT imagery. According to this principle, it will not be too difficult to realise above purpose on the series o available analytical plotter PLANICOMP.
The detailed procedures will be demonstrated through fig.1 and fig. 2.
According to this procedure it is very easy to introduce the corrections of image stage coordination into the Loop program in real time. The rigorous relationship between object and image point of SPOT imagery can be ensured.
