Anselm Schmieder
N
Sc 0 - OQ w^ A. O0
Processing of
two SAR images
Co-registration
Interferogram
en hy formation
/ Geometrical \ ____. -
\ information
eme ""Flat-earth'' phase
removal
Phase unwrapping
y
Phase to height
conversion
Figure 2: Derivation of a DEM from Interferometric SAR Measurements
. Let a polygon P be an ordered list of N points pj, ? — 1,..., N.
. Let ko be the number of points normally approximated by a single line. Let L4 — ppp; be the line connecting points
p and j.
. Letp=0)=0E=hk
. Test, if points j and k are approximate collinear. Let m be the point where E,,,, occurs.
. If the collinearity test is true, then La = p;pz, else let & = m and goto (4).
If np = j, then Z4, = La.
. If p Z j and angle between L,, La is small, then L1 = PpPr-
. If p # j and angle between L,, La is large, then p = j and L4 — L».
» Let 3. = kandk = k++ ke,
10.
If j < N— 1 then goto (4).
The Douglas-Peuker algorithm employs some predefined E,,,, value in approximation. A maximum distance criterion
for sequentially shrinking groups of lines is applied:
1.
2.
S.
6.
Let a polygon P be an ordered list of N points p;,? — 1,..., N.
Set index of anchor point a to a — 1 and index of floating point f to f — N.
Find point p;., where k lies in the range a, ... , f having maximum perpendicular distance d from a straight line pap;
connecting anchor and floating point.
if d > Frrox then let / = k.
ifd< Emarthena = fand f = N.
if a # f then goto (3).
The main evaluation point criteria for the three mentioned contour smoothing methods are the appearance of the line and
its error with respect to existing map products. Both issues will be addressed in the last section. Height inscriptions can
also be automatically derived, and the quality thereof can be evaluated by graphical attributes, which are: placement,
readability and direction.
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.
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