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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
42. 3D measurement in measurable seamless stereo model
The process for measurement on such a measurable seamless
stereo model is illustrated in Figure 3.
The corresponding points in the measurable seamless stereo
model (Manually measured or by image matching)
: t i
E pixel coordinate (1, J) in The pixel coordinate (Ig, Js) in
the orthoimage the stereomate
:
The planemteric coordinates
(Xs, Ys) in the stereomate
ge] DTM | —
Y
The planemteric coordinates
(X^, Y?) in the orthoimage
The planemteric coordinates
(X, Y) in the orthoimage
—p
Y
The 3D coordinates The 3D coordinates
(X, Y, 2) (CY, Z7)
i
Searching the original photo pair, which the corresponding point|
comes from
: |
The left (right) photo The right (left) photo
coordinates (x , y) coordinates (x' , y?)
| Space intersection |
:
The ground point
coordinates (Xp, Yp, Zp)
Figure 3. The 3D measurement in measurable seamless stereo
The 3D measurement steps in detail are as follows.
(i). For a given point on the stereo model, the corresponding
point on the stereomate is found by image matching. The
image coordinates are recorded separately as (I, J) in the
mosaic orthoimage and (I, J,) in the stereomate.
(ii). The pixel coordinates are separately transformed to ground
planimetric coordinates, to become (X,Y) and (X,Y).
(iii). For the planimetric coordinates (X, ,Y,) in the stereomate,
the planimetric coordinates (X, Y" ) in the orthoimage before
introducing parallaxes can be computed according to the
parallax function and DTM.
(iv). For the planimetric coordinates of a corresponding point
pair, (X, Y) and (X^, Y^), the heights Z, Z^ are bilinearly
interpolated from DTM. The 3D coordinates of the
corresponding point (X, Y, Z) and (X', Y', Z^) are then
obtained.
(v). The valid mosaic polygon to which the corresponding point
belongs is searched according to the planimetric ground
coordinates (X, Y) in the orthoimage. Then the original
photo pair, from which the corresponding point comes, is
also searched according to the valid mosaic polygon.
(vi) The coordinates (X, Y, Z) and (X', Y, Z^) can be
transformed into photo coordinates (x, y) and (x', y’) using
the known interior and exterior orientation elements of the
photos according to collinear equation.
(vii). The ground point (Xp, Yp, Zp) can then be computed
according to the forward intersection.
5. EXPERIMENTAL TESTING
According to theory and procedures described in the previous
two sections, a prototype the software SOD (Stereo Orthoimage
Database) is developed. Using in Visual C++.
Two sets of data with different photo scales and terrain types are
used to test the presented method and the software. The
parameters of the data sets are listed in Table 2. The pixel sizes
of the orthoimages for data sets I and II are corresponding
approximately to the footprint of the raw image pixels.
model
Table 2. The experimental data sets parameters
Item Data Set I Data Set II
Principle distance 153.710mm 304.034mm
Photo scale 1:25,000 1:8,000
Format 23cm X 23cm 23cm X 23cm
Overlap 60% 60%
Photo type Panchromatic False Color
Pixel size 25um 25um
Average flight height 4,225m 2,090m
Landform Hill mountain City area
GSD of DEM 12.50m 5m
GSD of orthoimage 0.65m 0.2m |
Data Range Five strips with five stereo models per strip Three strips with nine stereo models per strip
Figure 4 shows the result of the measurable seamless stereo
model generated from Data Set II. Figure 4a illustrates the valid
Mosaic polygons of the stereo photo-pair in the block area.
Every stereo pair has a valid mosaic polygon. Figure 4b is the
measurable seamless stereo model in red and green
complementary color mode. The stereo model can be directly
observed with red/green glasses. The 3D measurement of terrain
surface points and objects are performed on both two data sets.
For Data set I, twenty ground points were selected to the
accuracy test. These points are separately measured from
measurable seamless stereo model and from the original
photo-pair model at the SOCET SET v4.4.0 of Leica
Geosystems, Inc. The latter is used as the benchmark for
accuracy assessment. The maximum error and RMS error are
listed in table 3. Figure 5 illustrates the error distribution of
these twenty points.