33, 2012 
ints 
  
15° have been 
he pairs with a 
rmance of each 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
y. 
iS | LE90 
11 1.24 
73 1.14 
83 0.95 
69 1.01 
87 1.24 
66 1.08 
75 1.12 
73 0.99 
58 0.97 
96 0.99 
65 1.01 
72 1.08 
81 1.06 
90 1.14 
: 0.26-0.36) 
1S | LE90 
93 1.52 
97 1.52 
92 1.38 
78 | 1.24 
89 | 1.32 
01 | 1.34 
17 1.47 
ht — 0.18) 
shly dependent 
  
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B3, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
* A moderate stereo angle is definitely more efficient 
than a narrow angle in term of accuracy, with no 
difference, in term of completeness. 
  
wide base pairs + 
narrou base pairs 
280 + = , 1 
220 + + J 
nb of points 
180 r 4 
160 F 4 
  
  
140 € 1 L 1 i 1 i L L 1 
-50 -40 -30 -20 -10 0 10 20 30 40 50 
max incidence angle 
Figure 5 Completeness versus incidence angles 
  
We merged different combination of stereo measurements, 
using 3, 7 and 9 pairs. A first set is composed of wide angle 
stereo pairs, a second set is made from narrow angle stereo 
pairs. Our main concern is the evolution of the accuracy when 
the individual measures are aggregated. A decreasing RMS 
error would suggest the statistical independence of the different 
measures. The results below show that we are far from this 
situation. Aggregating 2 stereo pairs (3 images) improves 
clearly RMS and LE90 performances, but adding more images 
brings only a slight decrease in both values. In the case of 
narrow stereo angles, the aggregation benefit for 3 images is 
higher, but not sufficient to compete with the performance 
obtained from wide stereo angle measures. 
  
Incidences | Stereo | Images Bias | RMS | LE90 
-16.0..15.8 Wide 0.24 | 0.52 0.84 
-11.0..10.4 | Narrow 0.37 0.68 1.15 
-21.7..20.7 Wide 0.25 0.49 0.80 
-16.0..15.8 | Narrow 0.37 0.61 1.00 
-28.4.27.4 Wide 0.27 0.49 0.78 
-21.7..20.7 | Narrow 9 0.38 0.62 0.96 
Table 3 Multi stereo pairs 
  
  
  
  
  
OQ 
  
  
  
  
  
  
  
  
  
The benefit of the aggregation for the completeness is more 
obvious. For all combinations, the 295 check points are well 
defined in the aggregated DEM. This has to be also related to 
the perfect symmetry of the acquisition around a nadir image: 
This configuration minimises the hidden parts in a dense urban 
environment. Obviously, this condition cannot be met 
everywhere in the world because helio-synchronous satellites 
fly only along a finite set of orbits, which are generally not at 
the exact zenith of the area of interest. 
6. CONCLUSION 
We have presented a systematic exploration of the stereoscopic 
capabilities of Pleiades imagery for the extraction of digital 
elevation models in various environments. The agility of the 
satellite has risen questions about what is feasible, and what is 
efficient, regarding 3D mapping from multi-angle images 
sequences. As expected, the answer depends on the context. In 
an open landscape situation, without severe occlusions, a single 
stereo pair should provide a nearly optimal result with a fairly 
wide stereo angle. In urban area, the main profit of multi-angle 
  
  
  
Figure 7 Melbourne DEM (detail) 
images sequences is the reduction of occlusions behind 
buildings. A symmetric configuration with two oblique views 
on each side of a nadir image seems to be a good compromise in 
this context. Additional images acquired on the same pass 
would not increase the scene visibility and bring no significant 
accuracy improvement. The stereoscopic angle has to be 
consistent with the scene morphology to avoid occlusions but 
we did not get convincing results from narrow angles 
configuration.