Benedetto Villa
4. AERIAL PHOTOGRAMMETRIC SURVEY
Sample area was placed on two photographs related to a photogrammetric flight carried out over the Orleans Park in
1998, using a Wild RC 30 30/4 Nat-S camera with a focal distance of 300 mm and a Kodak Panatomic X 2412 colour
film. Photographic scale was about 1:3 000.
Also in this case the photo scanning was executed by a Epson GT 12000 scanner at a resolution of 800dpi.
Seven control points, surveyed by fast static GPS techniques inside Orleans Park, were used for the phase of the
absolute orientation.
Photogrammetric restitution, was carried out by Geotop RFD rel. 2.0 software. Afterwards, the vector file yielded from
restitution was processed by AutoCad rel. 14 software, also inserting topographic data particularly related to survey
architectural elements located on the ground surface (arcades, steps, pavements etc.). Figures 6 show axonometric
representations of the yielded 3-D model.
Figura 6. Wireframe 3-D model.
5. THREE DIMENSIONAL MODELS
Three dimensional models representing urban areas can be distinguished into 3-D wireframe models and 3-D
conventional and photorealistic models, depending on the kind of data they are based upon. Geographical space is
represented, in the first model, by vector data structure and, in the second one, by raster-vector structure.
The case study described below was carried out with regard to the second kind of models, the conventional and
photorealistic ones. Its aim was to find a suitable model both for planning and simulating the positioning of mobile
telephony antennas.
5.1 Rendered 3-D models
A rendered 3-D model is a digital representation which contains geometric data about the shape, dimension and location
of objects, described by using coloured surfaces. This allows a visualization of the terrain morphology, of the objects
surfaces and volumes, and of the lighting effects produced by natural or artificial light sources. Various methods can be
used to create such a model:
a) Draping of only one colour surface over the wireframe model in one step, so that a monochromatic visualization of
volumes is obtained. This method is quite quick, and requires only one command, if one already has a wireframe
3D model;
b) draping of various colours surfaces over the faces of a wireframe model, to display thematic data or to simulate the
quality of materials and surfaces;
c) draping of raster data over the faces of a wireframe model, in particular rectified photographs or orthophotos, in
order to obtain realistic data about facades and roofs. ;
Models a) and c) will be analysed below. They will be named monochromatic conventional 3-D model and
photorealistic rendered 3-D model respectively.
922 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.
