point set. A template window centering on the feature points
with different sizes (from 5×5 pixels to 40×40 pixels) was
extended to analyze the sensitivities of
SSSF
ncc
with regard to
changes of the template window size. At the same time, dif-
ferent canny operator thresholds (from 0.1 to 0.3) were set to
obtain different sharpness contours of the template window
(see Figure 8).
In accordance with the steps listed above, the
SSSF
descrip-
tor of the central point can be calculated using the shape
context algorithm (see Figure 9). In the matching procedure,
a search window of 20×20 pixels in the image was first pre-
dicted by the known geographic coordinates, and the
SSSF
ncc
was applied to extract the tie points via the template match-
ing strategy.
Figure 9.
SSSF
descriptors of some tie points: (a) optical-
SAR
1, (b) optical-
SAR
2, (c) optical-
SAR
3, (d) optical-
SAR
4, (e) map set.
Figure 8. Example of terrain contours from optical-
SAR
2.
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
October 2019
731
