CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
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A set of 713 high quality digital images were taken occupying 
an amount of 2,431 MB. 
3.3.2 Control point measurement 
As it was pointed in section 3.1, for the control points’ 
measurement a laser theodolite was used. With this instrument, 
control information can be rapidly achieved thanks to its red 
laser pointer. This pointer is really useful when poor 
illumination conditions exists. 
Control points for the whole building were measured according 
to a pre-defined ground coordinate system. Afterwards, their 
2D-facade coordinates were computed (when necessary) in 
order to perform the rectification process (see section 5). 
4. IMAGE POST-PROCESSING 
4.1 Radiometric correction 
In most of the works, making a good survey of the building is 
the main task, whereas taking beautiful pictures is not so 
important. In our case achieving good pictures was also 
relevant. As a matter of fact, it was requested that all the 
pictures were “equal illuminated for the human eye”. This was 
our main issue because of the so different natural illuminations 
of la Lonja's rooms. 
In some of the rooms, for instance the Capilla and the Torre, 
the poor natural and the absence of both natural and artificial 
illumination made necessary the use of some powerful 
spotlights. In the Salon Columnario was the other way round: 
the natural illumination was so strong that photographs had to 
be taken in the afternoon when the daylight was weaker. At that 
time, lights were already on. Another problematic room was the 
Escalera de Caracol. Besides its poor natural illumination, not 
artificial lights could be used because of the shadows, on the 
one hand, and the reduced space of the room, on the other. With 
respect to the building’s facades, photographs were quite 
homogeneous due to the cloudy weather during the fieldwork. 
Due to all this “in-field” problems, great effort was done in a 
post-processing step. Radiometric correction was required in 
order to overcome the matters appointed above. In figure 4 an 
extreme case is shown. 
Figure 4. Escalera de Caracol. Left: input image (original); 
Right: output image after radiometric correction 
4.2 Image rectification 
Some architectural ornaments had to be rectified for further 
plotting tasks. Additional photographs were taken for each one 
of the ornaments in order to ensure the best possible image 
quality. A minimum of four control points were measured for 
each photograph. The 3D control point coordinates were 
reprojected to the corresponding facades to obtain the 2D 
coordinates necessary for the two-dimensional projective 
transformation (Lerma, 2002; Hemmleb, 1997). 
Once the image rectification was performed, the Kirsch filter 
operator was applied to highlight borders and corners (see 
figure 5). 
A total of 72 ornaments were rectified. 
Figure 5. One of the rectified ornament belonging to the main 
facade. Up: original image; Down: filtered image 
5. DIGITAL CATALOGUE 
The realisation of a huge photogrammetric digital catalogue 
makes necessary a good data set management, including the 
image classification, data retrieving and visualisation. Without 
these, future work would not be an easy task. 
5.1 Image classification 
Photographs should be classified in such a way that makes it 
easy to relate them to the corresponding parts of the monument. 
This can be achieved by adopting a suited photograph’s 
labelling. 
For the photographs taken in la Lonja, a numeric labelling was 
chosen in such a way that all the following factors could be 
identified without any doubt: 
- The constructive parts of the building (patio, tower, 
etc.). 
- Facade, ceiling and/or ground. 
- Level of the photographic shots. 
- Number of the photographic shots. 
- Principal distance of the camera. 
Therefore, the photograph labelling was composed by a total of 
six digits where: 
First digit: