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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
2000). The test field in Frederikstad, Norway, has been flown
by two companies producing suitable GPS/IMU equipment,
namely Applanix of Toronto, Canada, using their system
POS/AV 510 and IGI mbH, Germany, with the system
Aerocontrol 11. Both companies have made calibration flights in
the image scales of approximately 1:5000 and 1:10 000 and a
flight for testing the results in the scale 1:5000. The targeted
control points of the test field are available with accuracy below
+/-1cm for all coordinate components.
The focal length was introduced as unknown during the
computation of the boresight misalignment. Depending upon
the data set and the type of computation, based on both flying
heights there have been significant corrections to the focal
length from 41pm up to *50pm. Also the location of the
principal point could not be neglected. Intensive tests with 11
system calibrations have been made by the Finish Geodetic
Institute and the National Land Survey of Finland (Honkavaara
et al 2003) showing improvements of the focal length up to
45um and significant changes of the principal point locations
up to 40pm.
The discrepancy of the interior orientation parameters cannot be
neglected. The knowledge of the actual focal length is
important for a flight over the project area with a different
flying height above ground like during the reference flight. The
location of the principal point is also important if the flight
direction will not be the same — like usual. But the location of
the principal point can be determined with a reference flight
only on one height level, flown with opposite directions.
4. INFLUENCE OF THE GROUND COORDINATE
SYSTEM
Block adjustments and also the whole photogrammetric data
handling are usually made in the national coordinate system.
They are not orthogonal systems and do not correspond to the
mathematical model used in photogrammetry. The national
coordinate systems are map projections and do follow the
curved earth. The difference between the curved earth and the
correct mathematical model is causing mainly a deformation of
the vertical coordinate component. It is usually compensated by
an earth curvature correction of the image coordinates.
The earth flattening by the net projections is deforming the
geometric relations. All modern national net projections are
conformal — over short distances the angular relations are not
influenced by the projection. This only can be reached if the
enlargement of the AY, which is caused by the convergence of
the lines perpendicular to the reference meridian, will be
compensated by a local enlargement of the AX (see figure 2).
So we do have a local change of the projection scale
independent upon the direction (formula 1).
Figure 2. net projection
SO = scale factor for reference meridian
R = earth radius
X = distance from meridian Formula 1: local
scale of transverse
x Mercator system
scale = S0e|1+ :
This local scale change is valid only for the horizontal
components X and Y. The height has a different definition and
is independent upon the net projection; it has always the scale
factor 1.0 leading to an affinity deformation of the three-
dimensional coordinate system.
Z
A /A
/A
distance
—» from center
meridian
Figure 3. influence of the national net scale to the exterior
orientation
Only one average scale for all three coordinate components will
be determined by the image orientation. Caused by the limited
Z-range the vertical control points usually have no or only a
negligible influence to the model scale. The horizontal scale
will be used also for the vertical component that means the
heights are directly affected by the local scale of the national
net. The scale for the reference meridian of UTM-coordinates is
fixed to 0.9996 causing a deviation of 4cm for a height
difference of Ah-100m at the reference meridian or 40cm
difference for a flying height above ground of 1000m. The scale
factor of UTM-coordinates goes up to 1.001 corresponding to
Im over 1000m.
The influence to the ground heights is usually within the
accuracy range of the point determination. This is different for
the projection centre. For the OEEPE-test on “integrated sensor
otientation” the distance from the reference meridian is in the
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