The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008
1318
AX
(longitude)
AY
(latitude)
Circular
Error
Mean (m)
3.3
-2.1
-
STDEV (m)
5.2
4.8
-
Max (m)
17.2
12.2
18.2
Min (m)
-10.7
-11.2
-
90% (m)
-
-
12.1
98% (m)
-
14.9
Table 4. Statistics on coordinate differences and circular errors
of the 120 checking points
The statistic of the 120 checking points (Table 4) shows that the
circular absolute horizontal accuracy is less than 12.1m for 90%
of the points, far within the CE90 16m specification of
Reference3D. Actually the absolute circular error is less than
15m for 118 out of the 120 points (98%). Table 4 and Figure 12
show a horizontal bias of 3.3m to East and 2.1m to South. Once
this bias is removed, the horizontal circular accuracy will be
improved to better than CE90 10.2m (Gray circle in Figure 12).
5. CONCLUSION
The accuracy of the Reference3D product was assessed against
the Japanese Triangulation Network, GSI DEM and 1:25,000
scale vector maps.
The comparison against the highly accurate DEM of the
triangulation network shows that the assessed Reference3D tiles
perform better than its specification, with a LE90 error of 6.7m.
During the assessment against GSI DEM, Reference3D was
transformed to Tokyo datum, and then the 1 arc-second (approx.
20m by 30m) Reference3D DEM was compared to the 50m GSI
DEM. The statistics of the vertical assessment show that the
DEM of the Reference3D meets its specification. The
assessment also shows that the Quality Masks is very useful
when judging possible error sources for location with
significant errors. With a smaller posting size than GSI DEM,
Reference3D is a good alternative DEM solution over whole
Japan or other areas for applications needing high consistency
over large territories (e.g. for mapping needs).
The horizontal accuracy of the Reference3D orthoimage,
assessed over the Japanese territory against 120 checking points
extracted from GSI 1:25,000 map, is absolute CE90 accuracy of
12.1m. This shows that Reference3D is a very powerful tool to
build highly consistent frame over areas that were once very
difficult to map with a good accuracy, such as, by instance, the
neighbouring Northern Islands.
ACKNOWLEDGEMENTS
The authors would like to acknowledge Mr. Fabrice Triffaut
from Tokyo Spot Image for his assistance in providing the
Reference3D tiles.
REFERENCES
Bouillon et al.,2006, SPOT 5 HRS geometric performances:
Using block adjustment as a key issue to improve quality of
DEM generation, ISPRS Journal of Photogrammetry & Remote
Sensing 60 (2006) 134-136.
Kay, Winkler,2004, Quality checking of DEM derived from
satellite data (SPOT and SRTM), 10th Annual Conference on
Control with Remote Sensing of Area-based Subsidies.
Budapest, 24-27 November 2004.