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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BI. Istanbul 2004
surface of the objects. Position and orientation data were
utilized to determine the viewing and illumination geometry
relative to the object surfaces. Classification and field
investigations were used to identify and delineate the sampled
natural and built objects. Algorithms for reconstructing the
image acquisition and retrieving image samples with known
geometry were developed, implemented and tested.
Directionally defined reflectance data were acquired to be used
in correction for bidirectional effects on aerial images and for
establishment of a bidirectional reflectance database.
First experiments of the data show the potential of the method
in the extraction of reflectance information from digital multi
angular images. The use of high-resolution surface models for
this purpose gives an interesting opportunity to investigate large
objects in a detailed manner. If well defined, the objects under
study will even be processed one by one and the data gathered
from multiple instances of a same type of object can be
combined in a convenient manner.
Data also demonstrate the potential of using the bidirectional
data in the extraction of tree species information; i.e. the 3D
presentations for each of the species differ significantly from
each other and the within species variation due to changes in
viewing and sun angles is prominent (see figure 5). Thus, it
seems that for example the tree species can be determined more
reliable by using multi-angular measurements.
The most remarkable angular uncertainty cumulates from the
digital surface models. The accuracy of the surface orientation
may be improved by replacing the image-based DSM with a
surface model derived using a high density LIDAR data
(Hyyppi et al., 2001; Kraus & Pfeifer, 1998; Pyysalo, 2000).
This could provide more detailed and precise surfaces for
BRDF sampling purposes. Also, improving the spatial and
height resolution of the surface models to a corresponding
image resolution or even better would be worth considering.
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ACKNOWLEDGEMENTS
The Academy of Finland, Jenny and Antti Wihuri foundation,
Finnish National Technology Agency and Foundation of
Technology are gratefully acknowledged for financial support.
