Estimation of Image Distortion Parameters
Activities start with the selection of a well distributed
coarse grid set of reference points (ground control points
GCP's and homologous points HP's) from browse or standard
product image data fig.2. All point positions will be
defined in image coordinates (line and pixel no.) by
digital correlation of radiometrically corrected image
data.
This actual point positions will be compared with modeled
point positions in a least squares balancing process. Model
point positions will be calculated based on orbit and atti-
tude orientation parameters and geometric transformations
representing camera geometry, rotating earth shape model
and, if required from the GCP-library, special map pro-
jections.
DFVLR will try more than one model approach. Present simu-
lations are based on functional and also on statistical
models of satellite orientation parameters. Results will
be presented and published on ISPRS Commision I meeting
Sept. 86 at Stuttgart.
The estimated set of parameters will be used to establish
a functional model of the image distortions. This model
defines relationships between the MEOSS image data and the
earth reference surface or the reference Surfaces of speci-
fic map projections. Terrain height effects will not be
considered and not be corrected.
This model also defines the relative distortions between
the three MEOSS image Stripes. From this results a func-
tional description of the curved "epipolar" lines which
must be followed for terrain evaluation in the original,
uncorrected MEOSS images. Thiswise the model will help to
avoid intermediate resampling processes if digital image
evaluation can be applied. (See lower part of fig.2)
Geometry of MEOSS Image Products
To render possible terrain height evaluation also by
photogrammetric standard equipment, DFVLR will offer
geometrically corrected (resampled) images, called pre-
cision products on CCT and film. These images will be
presented in a "Pseudo Space Oblique Mercator" PSOM
projection, corrected for satellite orbit and attitude
variations but not corrected for perspective.
Hence, the images will show the: typical "split" perspec-
tive of a CCD linescan camera: central perspective in the
direction parallel to the CCD Scan lines and parallel
perspective (vertical, foreward or backward inclined)
in the direction vertical to the scanlines. For illus-
tration see fig. 3.
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