International Archives of the Photogrammetry, Remote Sensing and Spatial Information
Fig. 7: Volume model illustrated as a wire frame (left) and as a rendered visualization (right) of Celle castle
depending on the amount of features.
AutoCAD offers the functionality for file export to several
visualization software packages, e.g. 3D Studio VIZ/MAX. The
3D volume models were transferred to 3D Studio VIZ using the
file format 3ds. Unfortunately, pre-defined texture mapping
from AutoCAD cannot be supported by 3D Studio. The data
export from AutoCAD to 3ds files must be carried out in
several steps due to the complexity of the volume models. This
characteristic effects that new layers have to be created with a
reduced number of 3D objects and /or 3D areas in order to
manage the complete data transfer. Thus, for each new layer
one new 3ds file is generated.
5.2 Visualization of the castles
Although the generation of perspective scenes of the 3D models
is possible with AutoCAD including texture mapping, the major
work for visualization of the three virtual 3D models was
performed in 3D Studio VIZ (release 3i), a light version of 3D
Studio Max. For photo-realistic visualization of the three castles
several video sequences and perspective scenes were generated.
As an example one perspective scene of cach castle is
illustrated in Fig. 9. The following processing steps have to be
performed in 3D Studio VIZ to achieve such results: a) import
and merging of all 3ds files; b) grouping of objects regarding
the later texture mapping; c) definition of materials including
import of the related texture files; d) manual texture mapping
for all objects, specially regarding the inclination and rotation
of each object element; e) illumination (e.g. sunlight) of the 3D
models; f) definition of special effects (e.g. radiosity,
atmospheric weather); g) definition of the camera and its path
for the video sequence; h) preview and final generation of a
video sequence.
The production of video sequences requires necessarily high
computer performance. For example, the computation of the
first video sequence of one minute (AVI format) for
Ahrensburg castle, which consisted only of the building (28MB
3D Studio file), in the resolution of 800 x 600 pixels took
approx. 22 hours processing time on a standard PC from the
year 2002 (PIII, 800 MHz, 256 MB RAM). In total 1800 frames
(30 frames/s) were generated, which corresponds to a
processing time of 1.3 minutes per frame on average. The
generated file size is 71MB. In comparison, processing took 7.7
minutes per frame (800 x 600 pixel) on average for a 3D Studio
VIZ file of 410MB, which includes the castle of Ahrensburg
and the park with photo-realistic texture mapping for the
building, the trees and the immediate terrain environs.
Therefore, the processing time was 102 hours in total on the PC
mentioned in chapter 5.1 for a video sequence of 60 seconds
(AVI 196 MB).
6. ECONOMICAL ASPECTS
Although it is fascinating to look at the projects from the
technical and realisation point of view, it is absolutely
necessary to analyse the projects from an economic perspective.
Therefore, the total processing time needed for the project Celle
was approx. 1350 hours, which corresponds to €54,000 in total
(calculated with an average wage of hour of €40). For the
analysis of the project the whole workflow was divided in
several working steps and the processing time needed was
estimated. The results are presented in Fig. 8 as a percentage of
each processing step. It could clearly be shown, that more than
65% of the time needed was used for the time-consuming CAD
reconstruction and visualization, while the geodetic and
photogrammetric project work amounts to just 35%. In this
estimation only the visualization with AutoCAD is included.
This result presented here can be confirmed by the analysis of
similar projects conducted at the HAW Hamburg.
1. Project planning 2. Photogrammetric and
3% geodetic recording
5 0
| | 3. 3D geodetic network
7. Visualisation in AutoCAD Pad — adjustment
12% \ giu n
4. Photo orientation, camera
calibration
10%
5. Photogrammetric 30
evaluation
13%
Fig. 8: Estimated time needed to complete project Celle castle
7. CONCLUSIONS AND FUTURE
These three projects demonstrate that commercial digital SLR
cameras are suitable for a detailed 3D evaluation and
reconstruction of large complex historical buildings. Due to the
digital data flow architectural photogrammetry has now become
an efficient alternative to the classical building measurement
and reconstruction methods. In each project an accuracy was
achieved in the range of 1-2 centimetres, which is sufficient for
most building applications. However, an important condition
tor such accuracies is the on-the-job calibration of the non-
metric camera, which can be performed simultaneously with the
determination of the photo orientation in the bundle block
adjustment. The detailed project processing of the Celle castle
Sciences, Vol XXXV, Part BS. Istanbul 2004
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