GPS VIRTUAL STATION TECHNIQUE (GPSSIT) AND ITS CHALLENGE IN
TERRESTRIAL PHOTOGRAMMETRIC APPLICATIONS
O. Corumluoglu *, I. Kalayci *, S. Durduran *, C. Altuntas ^, I. Asri *, A. Onal*
Selcuk University, Engineering and Architecture Faculty, Geodesy and Photogrammetry Department, 42075 Konya,
TURKEY -
® Selcuk University, Sarayonu Higher Vocational School, Surveying Division, 42075 Konya, TURKEY —
© Selcuk University, Institute of Natural Sciences, 42075 Konya, TURKEY —
(ocorumlu, ikalayci, sdurduran, caltuntas)@selcuk.edu.tr
Commission III, WG V/4
KEY WORDS: Textured image, Digital Photogrammetry, 3D model, GPS Virtual Station, GPSSIT
ABSTRACT:
GPS Virtual Station technique fundamentally depends on determination of a virtual point by GPS that is just about 1,5 meters
above the ground or a platform surface and then to the use of it by other surveying and/or photogrammetric instruments such
as a total station and/or a camera. Thus, the technique offers a challenge in terrestrial photogrammetry to determine the
coordinates of control points distributed on each facade of any object in any size and in a reference system, which is globally
available, and without using a network of points set up on the ground and surrounding the object. The technique is also
capable of determination of camera perspective centre's coordinates by the use of GPS Virtual Station which is determined
by the GPS antenna. In this process, first, GPS antenna is set up on a tripod with a leveled triprach to collect GPS Virtual
Station coordinates and then it is removed from the triprach and replaced with a camera (i.e. digital camera) in a similar way
of that can even be followed with total station to be used for the measurement of control points on the facades. So, it means
that the network of points to be set up for the measurements of control points on the objects in interest and which is the most
cost effective part of a over all project is removed, no more hustle for it, and three unknown parameters are now known
values when considering that the camera perspective centre is determined as GPS Virtual Station, and so that the number of
control points on the facades can be reduced, and there is no location limitation for chose of points, so that they can freely be
chosen at any time (even in the middle of a measurement section if some kinds of problems are met, such as GPS signal
blockage and object coverage problems) at any where around the object and finally, every object measured using this
technique in any part of the world can easily and spatially linked and referred to one another with respect to the same
reference system.
In this study, the technique mentioned above was utilised to create a final product as an originally textured virtual reality 3D
photogrametric model of a historical site, which is a unique sample of a cultural asset remained from its own time. It is
Aladdin Mosque built up at the top of the Aladdin Hill where takes place at the centre of Konya. 3D model of the site is also
ready to be put into the internet and onto a CD to distribute and interact in a GIS environment. As a final outcome of this
study, it can be stated that the technique proposed here represents an encouraging performance in the point of accuracy, and
project speed and economy as well.
1. INTRODUCTION
Soft copy photogrammetry is one of the most rapidly
developed, cheapest and easiest phenomenons which
have been never experienced in surveying discipline over
resent years. It is the result of digital technology adapted
to photogrammetry. Digital technology offered great
opportunities for photogrammetrists to replace their old
techniques and huge and heavy devices such as optic-
mechanic even analytical streoplotters in different sizes.
It was a revolutionary achievement that
photogrammetrists ever met before (Fraser &
Edmundson, 2000). After couple of years, a second
achievement came true: that was the emerge of digital
cameras. At the beginning, they were useless for
professionals with 2 — 3 Mega Pixels. But now, they offer
more than 5 — 8 Mega pixels. These precisions are quite
encouraging especially for terrestrial uses in
photogrammetry. Meanwhile, most special challenge
which is most important than that occurred in
photogrammetry was achieved in the general frame of
spatial data collection content at the beginning of 80's. It
was the civil use of satellite systems for the spatial data
collection processes: So it is the use of GPS. These two
challenges in spatial data collection processes pushed the
societies to develop their information systems rapidly.
The third one is also an opportunity to obtain digital
images of several wavelengths from satellites. That is
now well-known remote sensing. These last two spatial
data collection techniques both can now be used for
certain cases in photogrammetry. For example, GPS is
used in aerial photogrammetry to observe perspective
center coordinates of camera onboard a plane and to
determine the coordinates of control points on the
ground. Remote sensing images from satellites in space
are also used in archeological and architectural
photogrammetries.
These three new age technologies are now available to be
used in terrestrial close range photogrammetry. Remote
sensing images are able to be used to obtain textured 3D
terrain models with 3D building models which rise up on
these terrain models. They can also be used to determine
environmental features such as roads that link other sites
to the mission area and etc. 3D building models can also
be created as models which are textured with original
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