inbul 2004
DIGITAL DEVELOPMENT OF A SMALL VALENCIAN TOWER
J.T. Lerma, R. V. Tortosa
ETSI Geodésica, Cartográfica y Topográfica. Universidad Politécnica de Valencia.
C? de Vera, s/n. 46022, Valencia (Spain)
jllerma@cgf.upv.es
KEY WORDS: Close Range Photogrammetry, Architecture, Archaeology, Cultural Heritage, Visualization, Documentation
ABSTRACT:
Warping of images dealing with cylindrical objects through monoplotting is an efficient tool for archiving, documenting and
analysing non-planar but mathematical surfaces. However, it is not usually implemented in most of the photogrammetric packages,
although there are many architectural objects, monuments and buildings, as well as industrial features inadequate for orthoprojection
but appropriate for development or cartographic projection.
This paper shows the background and the results of a new photogrammetric software called DesenRec (‘Desenvolupament i
Rectificació', Development and Rectification), ideal for full development of cylindrical shapes. A set of eight images was taken in
order to test, record and mosaic the outer walls of a small tower placed in the Valencia City centre. The tower is 6 m high with a
diameter of approximately 2 m. After warping each image a digital mosaic was created to plot and analyse the whole tower's shape.
1. INTRODUCTION
Terrestrial and close range photogrammetry are both much
more efficient and economic than a few decades ago, mainly
due to the advance of digital technology and the development
of powerful processing packages. Nowadays, the use of non-
metric cameras, without lack of rigorousness, opens new
market photogrammetric demands. Moreover, there are more
technicians interested in applying photogrammetric
procedures to their field of work. This reality can be verified
in specific markets such as architectural photogrammetry,
archaeological photogrammetry and/or industrial
photogrammetry, for instance.
The employment of digital images allows the generation of
high quality raster products, adding colour and texture
variables to the traditional line plottings. In the case of
architectural and archaeological documentation, digital
images themselves are an essential document in order to ease
the study of materials and damages, interpretations and
analysis of Cultural Heritage.
Projective transformation or rectification of images
corresponding to planar objects is a simple technique that
makes easy the documentation of walls, panels and facades.
In literature can be found many related examples, and its
mathematical model is well known (Lerma, 2002).
Unfortunately, not all the objects are planar or can be
partially considered planar. The existence of relief requires
other strategies to derive the digital model before warping,
e.g. stereoscopy, multi-monoscopic measurements. However,
it is also possible to take another approach: the unwrapping
or monoplotting of developable surfaces (Karras er al, 1997;
Hemmleb and Wiedemann, 1997). This is particularly
Interesting for documenting curved surfaces and frescoes,
arches, towers, chimneys, etc. Whenever parametric surfaces
such as cylindrical, spherical or conical ones can be found,
the development of original images is feasible.
This paper tackles the plotting of mathematical surfaces
particularised to the case of cylindrical objects. In fact, a set
of eight images was taken in order to test, record and mosaic
the outer walls of a small Valencian tower.
2. SOFTWARE DESIGN
We have ourselves designed and developed a new
photogrammetric application called DesenRec
(Desenvolupament i Rectificatió, Development and
Rectification) in order to solve, on the one hand, two-
dimensional transformations of planar objects, and, on the
other hand, digital developments of cylindrical objects. The
program is based upon monoscopic procedures and digital
images. The software DesenRec 1.0 (Figure 1) offers the
following features:
- A Object oriented language program.
- Camera calibration algorithms.
- Best mathematical fitting to features or
objects (planar and non-planar but
continuous).
- Determination of transformation
parameters between image and object.
- Gross error detection and statistical
analysis.
- Digital image development and/or
resampling.
- Image mosaicking.
Besides, it is not necessary to be an expert in close range
photogrammetry in order to run successfully the program.
Furthermore, it accepts many ways of control information
based on both image and object space.
3. TEST APPLICATION
Software DesenRec has been tested on many emblematic
monuments located at the Valencia region. The main
characteristic of all of them is that they can be modelled by
means of a unique mathematical expression.