This study aims is to analyze the effect of spatial accuracy of the control points on the
images geometric correction accuracy, and this is done by applying tests on the same
image (IKONOS), where polynomial transformations were applied using sets
of control
points, each with absolute accuracy different from the other. These points were
extrapolated from a 1/1000 topographic map and from a georeferenced MOMS satellite
image with geometric accuracy of 2m and measured by GPS. The study showed that it is
possible to obtain the most accurate geometric correction by using control points with
absolute accuracy close to the spatial resolution of the image. It also showed that the use of
more precise control points would not ameliorate the accuracy of the geometric correction,
because the measurement of these points on the image is limited by its spatial resolution.
The geometric correction of remote sensing images becomes a key issue in
production and updating digital maps, multisource data integration, management and
analysis for many geomatic applications. 2D polynomial functions are the most prevalent
to
achieve this correction.
Previous researches have shown that the application of 2D polynomials is
conditioned by the planarity of the terrain and the uniform distribution of ground control
points, but did not explicitly discuss the criteria for evaluating the success or failure of
their application. In this study, we will try to give some of these criteria and to develop
some old analog cartographic rules to suit the nature of the digital satellite images.
In this research, we discussed mathematical foundation for evaluating the precision
of control points- based geometric correction of satellite images. We have also tested the
effect of the topography of the imaged scene on this accuracy. The test has been carried out
by the use of satellite images extracted from Google Earth. These images cover some areas
in the city of Latakia in Syria. Also, control points have been extracted from Google Earth
and transformed into the Syrian stereographic coordinates system.
Results demonstrated that the second degree 2D polynomial is very suitable for plan
small scenes with uniform distribution of the control points over the entire scene.
