Seams or discontinuities in a composite elevation file will occur due to
differences in the
quality and accuracy of the input DEM data files.
These
seams must be corrected or minimized to provide the user with data useful
for a range of applications. Seams generally arise when spikes or an offset
occurs in elevations values between two DEM data files. An
edge matching operation is used to detect spikes or offsets along a seam. If
a spike is found the bad elevation is replaced by an bilinear interpolated
value. If an offset is found the edge-matching
algorithm forces the DEM to fit along the edge, respecting slope continuity,
and distributes the residuals of any mismatch outwards from the seam in an
inverse-distance-squared fashion. The magnitude of the
residuals will range from a few meters up to 60 meters. (courtesy of the USGS) |
