Neither the goals nor the procedures of 3D mapping are clearly defined yet
Lately we observe an amazing increase
in earth-observation platforms equipped
with ultra high-resolution imagers. With
the recent deployment of WorldView-1
we have reached the 0.5 m footprint level.
This raises the issue of 3D topo-mapping
from space, in a more pressing way than
ever before. Topo-maps of medium and
larger scales (1:50,000 and better) are still
missing in some parts of the world, in
others they are hopelessly outdated. Upto-
date aerial images, as a traditional data
source for mapping, are not always and
everywhere available. In contrast, highresolution
satellite images with stereo
capabilities constitute an interesting tool
for mapping and the image providers
advertise their use quite extensively.
Topo-mapping is worldwide controlled
by specifications, which may differ
from country to country. Therefore it is
difficult to give general recommendations
with respect to the question which
sensor would be feasible for which
map scale. In addition, digital mapping
is largely scale-free, which makes
the issue even more controversial.
In the literature we find many predictions
and recommendations on 3D mapping
from space, but mostly without substantial
empirical evidence. 3D mapping is very
often reduced either to the generation
of ortho-images or/and to the georeferencing
accuracy and DTM generation
accuracy. But mapping is much more,
as we all know. 3D mapping from
satellite imagery is still a topic which
causes many misconceptions. We hope
we can contribute with this paper to a
clarification of some of the issues.
What is 3D mapping?
A consistent definition of 3D mapping is
missing. We are well used to conventional
2D and 2.5D mapping, resulting in
an analogue map as final product. 3D mapping however gives us many more
options, but also raises more questions.
With such new technology of digital
mapping we have to address a number
of problems, which are not necessarily
all new, but so far only sparsely
treated in R&D. Among those are:
+ 3D mapping – how does this differ
from traditional 2D and 2.5D mapping?
+ Which objects have to be mapped and
at which resolution and accuracy?
+ How should truly 3D objects be
modelled in terms of geometry,
topology and possibly also texture?
+ How should these objects be
represented in the database?
+ Digital mapping - how much
automation is currently possible?
+ Image interpretation – which
pixel size do we need in order to
bee able to extract features and
objects that are required for topomapping
at a certain scale?
+ Image quality – what are the
differences in image quality (and
thus interpretability) between aerial
and satellite images of the same
Ground Sampling Distance (GSD)?
+ Orientation/geo-referencing – how
accurately can we georeference the
new satellite images (with and without
GCPs) in planimetry and height?
+ DSM generation – what are the
expected accuracies in automated
DSM generation, which parameters
determine the accuracies of the
DSMs and what is the reliability of
the estimated surface models?
+ DSM-DTM reduction - what are
the most successful approaches for
DSM to DTM reduction and what are
the main problems to be solved?
3D mapping requires totally new
approaches to modelling. Most of the
traditional procedures and commercial
software packages, which have been
developed under 2.5D assumptions will
inevitably fail under strict 3D requirements.
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