PRECISE GEOREFERENCING OF RECTIFIED HIGH RESOLUTION SPACE IMAGES
Büyüksalıh, Gürcan*, Oruc, Murat*; Jacobsen, Karsten **
* Karaelmas University Zonguldak, Turkey
** University of Hannover, Germany
WG I/5
KEY WORDS: high resolution space imagery, direct sensor orientation, geo-reference, RPC
ABSTRACT:
The high and very high resolution space images are often not available as original or near to original data but as geo-referenced
rectified images. The geo-reference is based on the satellite position together with the known attitudes. In the case of IKONOS as
lowest level product the CARTERRA Geo, a projection of the original image to a plane with constant height is distributed. For
QuickBird the Basic Imagery which is just improved by the internal geometry, is available only as a full scene; less expensive sub-
scenes are distributed as Standard Imagery rectified to the rough digital elevation model GTOPO30 or as Ortho Ready Standard
Imagery rectified to a plane with constant height like CARTERRA Geo. Also SPOT images are sold as corresponding level 1B-
product like also IRS-1C/1D, ASTER and KVR-1000 data.
With additional cost for some products the relation between such rectified images and the ground coordinate system is available as
rational polynomial coefficients (RPC). The direct geo-reference for the RPCs is not accurate enough and has to be improved at least
by a shift to control points. Other solutions are approximations and don’t use the direct sensor orientation like the 3D-affine
transformation. In some orientation programs the original images are reconstructed based on the rectified images like described by
SPOT Image. For the precise geo-referencing the datum shift or higher degree transformation in addition to the terrain depending
improvement based on the height differences of the individual points against the reference plane has to be determined. This requires
the knowledge of the imaging ray from the actual projection centre to the point in the rectified and geo-referenced image. The view
direction from the scene centres to the satellite orbit is available in all cases. Based on this, together with the general known satellite
orbit, the individual view directions can be reconstructed without additional information. This strict solution requires the smallest
number of control points like also the RPCs, but without additional financial effort.
In the area of Zonguldak, Turkey several very high and high resolution space images are available as rectified and geo-referenced
products. The precise geo-referencing of these scenes has been made by GPS control points by means of the described method,
reconstructing the direction of the imaging rays and requiring only a minimal number of control points.
1. INTRODUCTION
The use of the full geometric potential of high and very high
resolution space images requires a correct mathematical model
or a three dimensional interpolation function which is based on
the sensor geometry and orientation. Also some three
dimensional interpolation models based on control points are
used, but they do need a higher number of well distributed
control points. Today the very high resolution space sensors are
equipped with positioning devices like GPS or DORIS and the
attitudes can be determined with a combination of giros and star
cameras allowing a standard deviation of the coordinates in the
range of 12m or even better. In relation to the pixel size this is a
limited accuracy, but together with the high relative accuracy
within a scene it may be useful for some applications. For a
higher geometric quality control points are required.
2. GEOMETRIC MODELS
2.1 Basic geometric relation
The high and very high resolution space sensors are equipped
with CCD-lines. Most systems do have a combination of some
shorter CCD-lines or small arrays. The relation between them
belongs to the sensor calibration which will be done in advance
by the data distributor. The user is getting only corrected data
sufficiently corresponding to an image taken with one
homogenous CCD-line with perspective geometry. The
combination of the CCD-lines in the orbit direction is
depending upon the change of the sensor direction in relation to
the orbit.
ON
Figure 1. imaging with the | Figure 2. imaging against the
orbit direction orbit direction
The very high resolution space sensors are equipped with fast
rotating giros, the so called reaction wheels, allowing a fast and
precise change of the view direction. The IKONOS satellite is
able to take images also against the orbit direction (figure 2)
without loss of accuracy. SPOT 5 is changing the mirror
orientation continuously for the compensation of the effect of
the earth rotation which is causing a deformation of the covered
