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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
the image using wavelet transform technique. It allows a higher
lossy compression rate compared to other compression
algorithms while preserving image quality (Santa-Cruz, 2000).
[Implementation of JPEG2000 compression on the hand-held
device requires sufficient CPU because intensive computation is
performed.
3.4 Processing Center
The PC comprises of three units used in a client-server
organisation. One is devoted to interact with the MGI or the OC
and is call the front-end server (FES). The second one, the
processing server (ProcS), will perform high intensive processing
tasks of image processing and is built on powerful hardware
components. The third one, the production server (ProdS), will
perform production tasks in order to make available the results to
the Internet community. All of the units are linked to a single
database DBrep containing acquired images and corresponding
processing parameters. Communication between the stations is
based on common web service protocols using SOAP messages.
3.5 Human-machine interaction
One of the key point of the system is the semi-automation of the
functions as, in the field of photogrammetry, it is still uncertain
to automate all the processes. So an efficient human-machine
interaction should be realized for the visualisation of either 2D or
3D information through Internet.
Nowadays two multi-platform technologies supporting 2D data
are identified: Java and PHP. Both allow to build dynamic user
interfaces linked with image server. The following two
implementations exist but still require assessment and
comparison:
1) Timemap: http://www.timemap.net
2) Mapserver: http://mapserver.gis.umn.edu
Concerning the visualisation of 3D data, more intensive
processing will be required on client side. So it is not likely that
this will be available on the MI. Only OC will efficiently be used
to manipulate 3D data. However 3D visualisation on PDA is
possible using VRML tool (see Cortona:
www.parallelgraphics.com) but, due to the reduce size of the
screen and the low CPU performance, this is not fully efficient
for complex textured model.
3.6 Quality requirements
Quality requirement of the telephotogrammetry system is
adjustable and will depend on the device preparation by the user.
Quality is improved by performing the optional tasks described
in Table 3.
Lens calibration
Colour calibration
Band alignment
| Resampling enhancement
_Positional precision | GPS measurement post-processing
Table 3: Tasks to improve system quality
| Image quality
4. USE CASES
In this chapter, the reader will find a description of various use
cases of telephotogrammetry.
4.1 Image mosaicking
One of the basic processing levels is the mosaicking of sequence
of images. It aims to combine images in order to obtain a
uniform view of the scene. Such a process alters the geometry
and the radiometry of the images.
An alternate goal is to improve the resolution by incorporating a
number of overlapping images of the same scene, a process often
called “super-resolution” in the literature. During the resampling
process, it results in a finer grid size.
4.2 Remote measurement
Once orientation of a sequence of images is performed, the
metric of the scene may be reconstructed, thus enabling direct
distance measurement on images. Relative or absolute distances
may be obtained according to the use or not of GPS data.
4.3 Rapid scene mapping
Simultaneous collection of images and positioning coordinates
opens wide applications for the purpose of rapid scene mapping
in case of crime, accident or even disaster (Gibson, 2000). It
seems important to quickly collect georeferenced terrestrial
image as a reference and as a basis for further 3D modelling.
Reference image may be distributed to different entities in order
to document real circumstances. 3d model may help understand
the causes for the event to occur.
4.4 3d modelling
3D modelling of real object may be done based on a sequence of
oriented images. This task is quickly implemented because of the
availability georeferenced terrestrial images. Modelling is
commonly done manually by visual interpretation. This provides
large perspective in the field of architecture.
4.5 Build image database
Taking advantage of simultaneous acquisition of image and
coordinates enables to build image database and subsequently
allows to query images from de database. This is especially an
application field for non-specialized end users.
4.6 City model building
Simplified acquisition of 3D model in mass using
telephotogrammetry system might lead to the possibility to
generate city models at a lower cost and shorter time.
4.7 Landscape assessment
Another field of application is the assessment of landscape. We
consider here either urban or natural landscape, and its change
through different time-scales: monthly, seasonal and finally
yearly. This is a further enhancement of 3D city model, in which
we include not only the natural environment but also its dynamic
through time.
5. CONCLUSION
The general framework for telephotogrammetry as described here
opens wide perspectives as to the exploitation of geo referenced
terrestrial images. It is expected that such a tool will promote the
use and exchange of 3D information and further stimulate the
development of location based services and other applications
like navigation based on three-dimensional city models or mobile
augmented reality.
