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Figure 3: Location of control, check and tie points in the
THR image
3.4 Bundle Adjustment
In order to compensate for possible systematic errors in
either the exterior orientation or/and the interior orientation
data (look angles) of SPOT-5 a new functional model is
implemented into ICC's adjustment software GeoTeX
(Colomina et al., 1992), which is described in the following.
The idea behind is to estimate global correction terms of the
given position and attitude of one common trajectory for all
cameras and also of the given look angles for each single
camera. As correction functions serve 3 order polynomials.
3.4.1 Functional Model
The functional model is based on equation [1], which relates
the look direction vector u, in the navigation reference frame
to the look direction in the terrestrial coordinate frame,
defined by the subtraction of the projection centre vector [Xo,
No Za. from the point vector [X, Y, Zr
- tan(y, ),, des A
U, T tan(y )o = A. ; Re ; Y RT Y, [1]
24 5 zu.
where
u, defines the look direction vector in the navigation
reference frame. It depends on the look direction angles
(Wx), and (¥y),, which are given for each pixel p of the
sensor line).
R,, transforms the navigation reference frame into the orbital
frame. It depends on the interpolated attitude angles a(t),
a,(t), a,(t) around the roll, pitch and yaw axes at time t,
which are given as a time series at 8 Hz frequency.
R5; transforms the orbital frame into the terrestrial frame. It
depends on the centre of mass position P(t) of the
satellite and the velocity vector V(t), which are given as a
time series at a 30 second time interval.
Eliminating the scale factor u the applied pseudo-observation
equations [2] are obtained:
s nC - X n Q -h)t*tn(Z - Z)
nO - XornmQ-Y)enmz-2z)
Oe EX > An) th -Y)rm(Z-2)
X A) (Ya) (Z Ze)
—tan(y, ),
+tan(w,),
with A
R - R5 a, (0.4, (0.2, ()] R2 [PG (0]-
Fi fü. "s
mm FP I5 [3]
Fa foo fus
The coefficients of the correction polynomials are the actual
unknowns of the adjustment, which are applied to the
parameters of the external orientation E, (equation [4]), i.e. to
the position vector P(t)=[Xo, Yo, zr and to the attitude
angles a(t), ay(t), a,(t) as well as to the parameters of the
internal orientation I. (equation[5]), i.e. to the look direction
angles (Wx), and (Fy), of sensor line S and pixel p.
E-ZE -AÀ,*B,(t-t)- C,(t - ty 9 Dj(r- ny
[4]
Pelle Bey EEE Ley DEP:
p / ;( 1000 ) 1 1000 ) i 1000
[5]
The external orientation parameters E (equation [4]) enter in
the equations [2] and [3]. They are derived from the
interpolated parameter E, at time t of the corresponding
image line and the 3" order correction polynomial with its
unknown coefficients Ag, Bp, Cg and Dg. tc here is defined as
time of the central line (212001) of the THR image. The
internal orientation parameters I? (equation [5]) also enter in
equation [2]. They are derived from the parameter LS of the
interpolated sensor position p and the 35 order correction
polynomial with its unknown coefficients AS, BS, CP and
Dj. pc here is defined as the centre pixel of the respective
sensor line S.
This model involves 48 unknowns, if 3 viewing directions
are involved (like in this evaluation: HRS1, HRS2 and THR),
ie. 4 unknowns for each of the 6 external orientation
parameters and 2 x 4 unknowns for each of the 3 sensor lines.
In practice only a subset of these 48 unknowns will be
significantly determinable and the rest of the parameters need
to be fixed in order to avoid over-parametrization problems.
3.4.2 Input
The following observations are introduced into the
adjustment:
— Image coordinates of 19 control and 17 check points
(020.5 pixel), measured in the HRSI, HRS2 and the
THR images (see figure 3),
—