Study on generation of DTM using SPOT stereo data (II)
SPOT Data
Two scenes of SPOT level 1A panchromatic mode CCT were used for this study. The image processing and the test of bundle adjustment program for ground coordinate computation were accomplished by using these two scenes and Numerical data from CCT header file and imagery files.
The stereo pair used in this study is shown in Figure 1, and the general descriptions are described in Table 1. The convergent angle is 300 04', and the B/H ratio is 0.54.
Table 1. General Descriptions of SPOT scenes
| |
Left Scene |
Right Scene |
| Sensor |
HRV 1 |
HRV 1 |
| Column - Row |
305-273 |
305-273 |
| Preprocessing level |
1A |
1A |
| Spectral mode |
P |
P |
| Observ. data |
16 Feb. 1987 |
30 Nov. 1987 |
| Incidence |
L 03° 54' |
R 26° 10' |
| Orientation |
11° 29' 12" |
8° 20' 20" |
| Scene Center |
38° 20' N
127° 47' E |
38° 20' N
127° 55' E |
Ground coordinates for control and check points were digitized from 1:50,000 scale topographic map using calcomp digitizer.
Mathematical Model for Bundle Adjustment
For level 1A panchromatic SPOT digital image, a full scene is composed of 6000 lines, and each of lines has 6000 pixels. The image coordinates of any point can be measured by line and pixel number of SPOT linear array CCD known as 0..13m X 0.013 mm in size which gives the ground resolution of 10m x 10m.
For the orientation of one line 6 parameters, i.e. orbit parameters (xo, Yo, zo) and attitude parameters (
w,
f,
c) are required. the sampling interval for two adjacent line is 0.0015 second. And differing from the cas of aerial photo orientation, the satellite attitude and the variation rate along the track are highly stable.
Due to the pushbroom scanning characristics and being highly correlated exterior orientation parameters between scan lines, we can reduce the large amount of parameters (36,000 for the whole scene) to the order of 12 to 21 or more by introducing the mathematical models of line function.
The modified collinearity equations for SPOT data are as follows:
xi +
Dxi = - f ( (m11t(Xi-Xt) + m12t(Yi - Yt) + m13t(Zi - Zt)) / ( (m3lt(xi-xt) + m32t(yi-yt) + m33t(Zi-Zt)) )
yi +
Dyi = - f ( (m21t(Xi-Xt) + m22t(Yi-Yt) + m23t(Zi-Zt)) / ( (m31t(Xi-Xt) + m32t(Yi-Yt) + m33t(Zi-Zt)) )
.............(1)
where
xi, yi : image coordinates
f : focal length
Dxi, Dyi : Systematic corrections for image coordinates
mllt - m33t : rotation matrix elements at line t
Xi, Yi, Zi : object space coordinates of point i
Xt, Yt, Zt: object space coordinates of projection center of line t
And
Xt = S Xn tn (n= 0-2)
Yt = S Yn tn (n= 0-2)
Zt = S Zn tn (n= 0-2)
wt = S wn tn(n = 0-3)
fT = S fn tn(n= 1-3)
kt = S kn tn(n= 0-3)
.............(2)
By linearizing equation A(1), the observation equations for collinearity condition can be achieved, and these equations are combined with the observation equations for ground coordinates and orientation parameters, which gives the mathematical model as follows.:
Eq. 3 & 4
