D-BAUG - Departement Bau, Umwelt und Geomatik - ETH Zürich

Highlights ▪ Geo-, Structural- and Environmental Data
Alignment of the future 50 km Compact
LInear Collider (CLIC) at CERN
What is horizontal ? High-precision deter-
mination of the geoid over short distances.
Although the world’s largest particle accelerator, the LHC
(Large Hadron Collider) at the European Organisation for
Nuclear Research (CERN), has started its operation only
very recently, the next generation of accelerators is already
under intensive study.The CERN explores the feasibility of
a new electron-positron linear collider of 50 km length
called CLIC (Compact LInear Collider). One of the biggest
technological challenges is the alignment of all components
accelerating and steering the particle beam in a
straight line. In fact, these elements must be aligned with
a relative accuracy of 10 microns per 200 meters (compared
to 0.1 mm per 100 meters for the LHC).
For the vertical component a solution based on a hydrostatic
leveling system (HLS) is under study giving promising
results. Nevertheless, this technique is limited, amongst
others, by the reference of the static water. In fact, the
equilibrium state of static water does not coincide with a
straight line, but matches the instantaneous equipotential
surface of the gravity field, the geoid, which depends on
the inhomogeneous density distribution in the vicinity. In
other words, the geoid has to be determined with an accuracy
of better than 10 microns per 200 meters, if instruments
depending on gravity (such as the HLS) are used.
In order to study the feasibility of this geoid determination,
extremely dense measurements of the acceleration of gravity
and the astro-geodetic deflection of the vertical are carried
out at the surface and inside a straight tunnel of 850
metres lengths at a depth of 100 m.The gravity acceleration
is measured by the new gravimeter CG-5 with a resolution of
one billionth of the Earth’s acceleration (g ≈ 9.81 m/s 2 ). The
deflection of the vertical is determined with an accuracy of
better than 0.1 arc second by the astro-geodetic system DI-
ADEM developed at IGP. The combination of these measurements
with geological information will be the basis to assess
the variations in the gravity field over such short
distances.
68 ▪ D-BAUG Annual Report 2009
Interactive Design of World Map
Projections
A new software-based approach to the
design of projections for world maps.
by S. Guillaume, B. Bürki / IGP von B. Jenny, L. Hurni / IKA
The design of new map projections has until now required
mathematical expertise that has limited this activity to a
small group of specialists. The Institute of Cartography
developed a new software-based method, enabling cartographers
to easily design new world map projections.
A new projection is designed interactively in an iterative
process, which allows the designer to graphically and numerically
assess the representation of the continents and
the graticule (the network of lines of latitude and longitude
upon which a map is drawn).
The devised concepts were implemented in Flex Projector,
a specialised free and open-source software application for
the design of new world map projections. It enables users
to quickly create new map projections and modify or combine
existing projections. Flex Projector also offers complementary
visualisations and numerical evaluation methods
that illustrate the distribution and amount of the
inevitable areal and angular distortion and help the projection
designer optimize a projection. Flex Projector was
used to create various new map projections, for example
the Natural Earth projection (Fig. 3), which is a pseudocylindrical
projection with a balanced appearance of major
landmasses. It was decided to give the corners, where
the pole lines and bounding meridians meet, a rounded appearance.
The rounded corners suggest that the projection
represents a spherical earth, and reduce the size of polar areas,
thereby reducing the areal exaggeration of Antarctica.