Egypt has launched its first Earth remote sensing
satellite EgyptSat-1 in 2007. A series of evaluations of the
usefulness and limitations of EgyptSat-1 images for
different applications are required. This research is
concerned with the investigation of the geometric and
cartographic potential of EgyptSat-1 image in order to
know to what scale EgyptSat-1 image is suitable for map
production and map updating. The geometrical accuracy of
rectification of EgyptSat-1 based on non-parametric rectification
(polynomial approach and rubber sheeting) has
been evaluated. Four methods of rectification have been
compared: different orders of 2D polynomials (first-order
polynomial, second-order polynomial, third-order polynomial)
and rubber sheeting method. Different sets of ground
control points (observed with differential global positioning
system) have been tested. Several experiments were
performed to rectify EgyptSat-1 image using the four
rectification methods. For each method, different numbers
of ground control points (GCPs) were used starting at 15
points, and then the number was reduced each time till the
minimum number of GCPs for each method is reached and
with three different GCP distributions. Various issues such
as the solutions, feasibility, accuracy, and requirements for
control information are addressed. The results show that
rubber sheeting followed by third-order polynomial then
second-order polynomial then first-order polynomial gives
the best root mean square error. Actually, a serious mapping
should be based on a satisfying by the theory justified
mathematical model so that rubber sheeting should not be
used for a serious mapping even it shows smaller discrepancies,
but for the flat test area, an approximate 2D
transformation can be accepted. Also although third-order
polynomial is accurate in the proximity of GCPs and shows
smaller discrepancies compared to the first- and the secondorder
polynomials, they can lead to significant errors for
regions outside the GCP range and should not be used for a
serious mapping. One can be considered the best resulted
rectified image that obtained from second-order polynomial
followed by the first-order polynomial. It was found in our
study area that the minimum number of control points for
each method gives accuracy better than a pixel. The firstorder
polynomial and rubber sheeting are good from the
economical cost that they use minimum number of control
points (three). It was found that the planimetric accuracy of
rectified EgyptSat image met the 1:25,000 mapping
standard (National Map Accuracy Standards). Also from
the assessment of the information content of the EgyptSat
image, it was found that it is consistent with the map scale
of 1:25,000. In conclusion by analysis of the results, it is
obvious that EgyptSat images are able to produce and
update map of scale 1:25,000. |
