2011 - Geoinformatics

[b]
the maze of underground tunnels lying beneath Dover Castle on the
cliff coast of south-east England facing France that have been constructed
for defence purposes over a period of several centuries;
and (iv) the World Heritage prehistoric (Neolithic) site of Stonehenge
with its famous circles of standing and fallen stones (dating from
around 2500 BC) and its surrounding ring bank and ditch earthwork
[Fig. 3]. Again the documentation resulting from these various
surveys in the form of images, maps, plans, 3D perspectives and
video fly-throughs was often eye-catching in the extreme.
Technical Sessions
The first of the technical sessions (TS-1) was entitled Sensor
Development & Mapping Solutions and featured several very interesting
presentations. Among these was that given by Konrad
Wenzel of the University of Stuttgart. He and his colleagues from
the University’s Institute of Photogrammetry have devised a low-cost
photogrammetric imaging system comprising five small-format cameras
equipped with very short focal length lenses and a near-IR random
pattern projector. All of these are mounted together on a
portable metal frame that can be used to undertake very close-range
imaging surveys [Fig. 4 (a)]. The highly automated processing of
the resulting data is then carried out using an image matching algorithm
that has recently been developed for use with very dense data
sets. The imaging system has been used to survey the huge triangular
stone tympana (each 25 m in width and 6 m in height) which
are mounted at the top of the façades of the Royal Palace located in
the Dam Square in Amsterdam [Fig. 4 (b)]. The scaffolding and
screens that have been erected to carry out the restoration of the
whole building [Fig. 4(c)] only allowed imaging distances of less
than one metre. With an object (post) sampling distance of 1 mm,
the point cloud that results from the images acquired at circa 2,000
different camera positions is simply enormous, as is the subsequent
task of processing this data mountain (or cloud). Another interesting
presentation in this session included a comparison of range-based
(laser scanner) techniques with image-based (photogrammetric) techniques
for the surveys and documentation of rock art shelters in Spain
that was given by Professor Lerma of Valencia Polytechnic. Yet
another eye-catching presentation was that given by Dr. Caterina
Balletti of the CIRCE Photogrammetric Laboratory of the IUAV
[a] [c]
E v e n t
Fig. 4 – (a) This photogrammetric imaging system
comprises four small-format digital cameras equipped
with short focal length lenses and filters that only transmit
near-IR radiation. The fifth camera transmits light in
the visible part of the spectrum and is equipped with an
even shorter focal length lens. The five cameras are
mounted rigidly on and are protected by an aluminium
frame. At the top of the frame is the projector from a
Microsoft Kinect device that projects a random pattern
in the near-IR part of the spectrum to provide additional
texture to the images. This helps with the later automated
image matching process. (Source: Institute of
Photogrammetry, University of Stuttgart)
(b) This triangular clay relief was made in around 1655
to act as a model for the tympanum mounted at the top
of the façade at the rear of the Amsterdam town hall,
now today's Royal Palace on Dam Square. (Source:
Rijksmuseum)
(c) The front façade of the Royal Palace with the scaffolding
and screens which have been erected during its
restoration. The Palace is located in the Dam Square in
Amsterdam. (Source: Institute of Photogrammetry,
University of Stuttgart)
University of Venice. This involved the survey of the historic buildings
lining Venice’s Grand Canal, which was carried out using a
boat-mounted Riegl VMX-250 mobile mapping system [Fig. 5] and
processed using Riegl’s RiPROCESS software.
The second Technical Session (TS-2), entitled “Imaging Solutions from
Aerial to Underwater”, proved to be no less interesting. Dr. Geert
Verhoeven from the University of Ghent gave an entertaining
account of the aerial photogrammetric survey of an ancient Roman
quarry located at Pitaranha in the central part of Portugal, close to
the Spanish/Portuguese border. This was implemented using a Nikon
D80 small-format (10 Megapixel) digital camera which was mounted
on a low-flying Helikite aerostat attached to a tether [Fig. 6]. The
Helikite is a combination of a balloon and kite that is manufactured
by Allsopp Helikites Ltd. in the U.K. The subsequent data processing
of the 1,000 often quite tilted images that covered the Pitaranha site
was carried out using the Structure from Motion (SfM) software that
is popular in machine vision and robotics to handle multiple-view
images. [N.B. The SfM software appears to implement a set of fairly
conventional multi-image photogrammetric solutions, even though it
uses a wholly different terminology to that in common use in photogrammetry.]
Also of much interest in this second (TS-2) session were the presentations
on the aerial surveys of heritage sites from low-flying UAVs.
The first of these was given by Greg Colley of sUAVe Aerial
Photographers, who used a Canon 5D camera mounted on a UAV
that was operated from a very low altitude to survey the Roman
Amphitheatre in Chester in north-west England. The second presentation
was given by Dr. Sara Bursanti of the University of Trieste.
She utilized a quadcopter UAV equipped with a Canon IXUS compact
digital camera to carry out a survey of the city walls of the
Roman city of Aquileia in north Italy - which is yet another site that
has been included in UNESCO’s World Heritage List. These two
presentations were supplemented by a poster by Andrew Blogg
of the KOREC company in the U.K., who brought along (in a suitcase)
and showed an actual example of the very lightweight Swinglet
CAM flying-wing mini-drone with its 80 cm wingspan that is produced
by the SenseFly company in Switzerland [Fig. 7]. It features
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