Neither the goals nor the procedures of 3D mapping are clearly defined yet
From 2d maps to 3d
landscape models
Worldwide databases like Google Earth
have given a wider audience access to georeferenced
data. This data is useful for all
kind of planning and inspection purposes,
but usually does not satisfy the demands of
a professional map user. However, it has
sharpened the mind for what can be done
with geo-data, in terms of visualization
and interactivity. And it has set a certain
standard in perception of terrain and
other geo-related data. Has Google Earth
even changed irreversibly our perception
of a map? If yes, then what do we, as
experts or occasional users, expect form
modern maps after Google Earth?
Mapping has grown way beyond the
traditional domain of topo-mapping
and thematic mapping. Markets for
geospatial technologies include nowadays
applications in insurance and risk
management, natural and man-made
hazards, real estate, Location-based
Services, environmental monitoring, car
navigation, oil and gas, homeland security
and many more. However, the data
contained in topo-maps (or “landscape
models”) can in the future serve as the
backbone of these diverse applications.
The flexibility in handling of and in
modifying digital data has brought up
the issues of “real-time mapping” (see
recent disasters in Myanmar and China),
“mapping on demand” (individualized
data collection), “personal mapping”
(representations for a particular purpose
or person). Mobile Mapping platforms
on cars, trains and UAVs allow for
real-time raw data collection at an
unprecedented speed and flexibility. New
devices like mobile phones and PDAs
in LBS-related applications bring up
the notion of “ubiquitous mapping”.
how does this all relate to
the task of topo-mapping?
There is a large amount of data already
now available which would qualify for
“3D maps”: 3D city models, forestry
models, Cultural Heritage models, etc.
Should this data form a joint database
with the more conventional content of a traditional
topographic
map?
This all requires us
to reconsider radically our mapping
goals, tasks, procedures and products.
First steps in this direction have
been taken. The Swiss Department
of Lands (“swisstopo”) has defined a
countrywide map system on the basis
of a Topographical Landscape Model
(TLM). This Landscape Model includes
all objects that are currently represented
in topo-maps, but in truly 3D form. This
includes terrain, buildings, water objects,
public transportation, public spaces and
facilities, landcover, administrative borders
and “points of interest”. Compared to
the situation before this model features
some novelties, as for instance
- It serves as the basemodel for the
whole country. Subsequent level
models for cartography and for
representation (at varying scales)
are defined, which are derived from
this unique dataset of the basemodel.
Therefore all the objects of the
basemodel are geometrically correctly
modelled. There are no displacements
of elements and no generalizations.
- The data is always actual. It is
continuously updated, and not
only at certain fixed intervals.
- The accuracy is very high. The
object accuracy is specified to 1 m.
- The data is truly 3D. Therefore all
objects can be correctly modelled and
no information has to be suppressed
because of lack of modelling tools.
- The data model is set up such
that it is ready for extensions.
At this point the data is still acquired from
aerial images, as of January 2008 only
from digital cameras like the Leica ADS40.
This Landscape Model is interesting from
a conceptional point of view. It remains
to be seen how it performs in practice.
3d landscape Models from
aerials or satellite images?
With the increased availability of ultra
high-resolution satellite images and (partially)
dropping prices
this becomes a burning question.
Both data sources do have distinct
advantages and disadvantages,
which are briefly listed here:
Pro satellite images:
• The satellite platform is operational
365 days of the year
• Frequent re-visit times (e.g.
every 4 days or even more)
• Imagery is post-processed
relatively quickly
• There are no Air Traffic
Control restrictions
• Large area footprints decrease
the need for block adjustment
and creation of image mosaics
• The satellite can easily access
remote or restricted areas
• No aircraft, cameras or otherwise
expensive equipments are
required (by the end user)
Contra satellite images:
• The image acquisition
geometry is not flexible
• The image resolution is fixed
for a particular sensor and low
compared to most aerial imagery
• The radiometric resolution is
often too low (problems in
shadows and saturation areas)
• The image quality is often impaired
by different factors and artifacts
• The typical off-nadir viewing
angle of up to 25˚ is problematic
in image matching
• The reliability of capture and delivery
of imagery can be poor at times
• Strong possibility of cloud
cover and thus occlusions
• The cost of the imagery may be too
high (when compared to aerials)
The selection of any one of the data
sources depends on many factors. The
decision can only be made efficiently
when all the project parameters are
available. We have reported about an
extreme case in Bhutan (Fraser et al.,2008), where access to aerial images is
impaired and where pilot projects are
underway to use satellite imagery for the
generation of a new topo-map 1:25,000.
In our following pilot test for topomapping
we compared map objects
derived from IKONOS 1m GSD stereo
images with map data from the Swiss
topo-map 1:25,000, which is usually
derived form aerial images at scale
1:30,000 (which in turn corresponds to
an image pixel size of about 0.5 m).
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