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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
1.3. Visualization of 3D Models
In the photogrammetric community, the first attempts in the
visualization of 3D models were done at the beginning of the
'90. Small objects (e.g. architectural models, cars, human faces)
were displayed in wireframe format or using CAD packages,
while terrain models were visualized in perspective wireframe
models with draping of orthophotos or orthophotomaps.
Nowadays, with the increasing of the computer memories,
shade and texture are added to all the models, but in order to
accurate visualize big data sets, much information contained in
photogrammetric models is often reduced. The consequences
are that the accuracy of the data is lost (many tools use single
precision files) as well as the geo-referencing (most of the
software has their own coordinate systems) and that high
resolution textures are unusable (because of the control on the
Level of Detail) On the other end, low accuracy in the
visualization does not attract the end-users and cannot justify
the high cost of producing the photogrammetric 3D model.
After the creation of a triangular mesh, the results are usually
visualized, according to the used package and the requirements,
in the following manners:
e Wireframe mode: It is the easiest way of representing a 3D
object. It consists of points, lines and curves and describes
only the edges in a transparent drawing, without texture or
shading information. This technique is mainly used in
computer-aided design (CAD) packages.
e Shaded mode: It is based on the optical theory (Lambert’s
Cosine Law) which states that the brightness of any small
arca (polygon) of a perfectly diffuse undulating surface
arises as the cosine of the angle of incident parallel light.
o Textured mode: It is used for photorealistic visualization of
the 3D models (image-based rendering). Texture mapping
in its simplest form involves a single texture (image,
orthophoto) being mapped onto the surface composed of
one or more polygons.
In general, creating realistic 3D models (shaded or texturized)
helps to visualize the final result much better than a wireframe
representation (Remondino, 2003).
2. CASE STUDY
In this study, a simple and a basic 3D city model is tried to be
built using different data sources such as terrestrial and aerial
photogrammetry, and different visualisation techniques. In the
first part, photogrammetric data acquisition method is used in
two applications, in two different places.
The first one is an Opera House in Hannover-Germany. In this
application we aimed to create a 3D building using one of the
terrestrial photogrammetry tool Photo Modeller Software and
visualize it in 3D with GIS environments. The second
application is in centre campus area of Blacksea Technical
University in Trabzon, Turkey. All centre campus area is
digitized from stereo images after stereo-photogrammetric
evaluation in Zeiss-SSK Software. Then buildings extended to
their original height in AutoCAD program. Finally, gained
vector data rendered with rectified photos for photorealistic
visualisation of 3D model.
In the second part, a 3D GIS application was done using the
photogrammetrically gained digital vector data in the first part
of study. Firstly a terrain model is created from vector data and
then a shaded 3D City model is generated over this terrain, with
a simple information system in ArcView 3.2.
At the end of the case studies, produced models are compared
with the view of usability and effectiveness.
2.1. First Part of Case Study
2.1.1. First Application
In this contribution, Opera House in Hannover (Germany) was
choosed and, eighteen photos that surround this building, which
were taken by one of the Institute of Photogrammetry and
Geolnformation’s staff in Hannover, were used. The images
were taken with Olympus E10 digital camera with 2240x1680
geometric resolution and 9 mm focal length. Photo Modeler
software by EOS Systems Inc. was used for photogrammetric
evaluation. The Canadian PhotoModeler Software Package is
well known as a low cost 3D-measurement tool for architectural
and archeological applications. It is a Windows based software
that allows measurements and transforms photographs into 3D
models. The image coordinates of corresponding points and
control points were measured manually and the images were
oriented automatically. After the facades of building was
identified as a surface patches, the wireframe and photo-texture
model were built up using the oriented images (Fig. 1).
11111114
m
F
4 Figure 1. Photo-texture Model of Building Created by Photo
Modeler
2.1.1.1. Visualization and Querying of the 3D Model in GIS
The 3D DXF file created in PhotoModeler is converted to SHP
file format in ArcView. Base map with control points is
imported to ArcView program. A georeferencing has to be done
to make association between base map and 3D model to see
them together in 3D scene. With the help of the TFW (world
file for tiff image) file belongs to ArcView, base map is
registered and transformed into same coordinate system with
3D model.
One of the main objectives of this application was visualizing
the photo texture in GIS environment. However, only the
shaded parts of the building can be seen in 3D in ArcView. For
this reason photo texture could not be used in a structure
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