External and Internal Surveying of a Construction Using Low-cost Equipment 
175 
Figure 3: Layout showing localization and identification 
of control points 
Coordinate control points were calculated using the software 
GEOD, developed by the Institut fur Photogrammetrie und 
Femerkundung, of University of Karlsruhe (Germany). 
DALLAS (1992) concludes that the difference in altitude 
observed between two instrumental stations (same control 
point) would not exceed a precision degree of 5mm. 
4.2. Photographic survey 
An OLYMPUS Camedia C-820L digital camera was em 
ployed for the photographic survey. As it is not a metric cam 
era, the Camera Calibrator 3.1 software was used so as to 
know its internal parameters. 
The Photomodeler's user manual recommend that a minimum 
of three images of the same control point be obtained. In this 
way, the geometric quality of a restored point increases, when 
the demarcation of it on other photographs also increases. 
Subsequently, planning of different photographic sectors in internal and external areas was carried out. In each sector, a minimum of 
one photograph perpendicular to the object and other two from each side at an angle of about 90° were taken. In the internal areas, the 
distribution of windows and doors influenced the use of daylight, electric light or curtain closure. 
202 photographs were taken during the whole study. Layout showing localization and coding individual identification of each photo 
graph was carried out on every area study. 
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Figure 4: Layout showing localization and identification 
of photographs 
4.3. Restitution in Photomodeler 
Taking into account that the aim was not to obtain a 3D lineal restitution of construction, a restitution of control and auxiliary points 
was carried out. 
Firstly, project restitution for each area of study was created. Objects and camera information was also incorporated. Secondly, con 
trol and auxiliary points were marked in one photograph and referencing other two photographs of the same sector. Then, restored 
points were processed and project quality data were analyzed by the same software. Finally, three new photographs were joined and 
the same steps were developed. The same was done with all the photographs of the projects. 
Project scaling was carried out using three points of the topographic survey. Finally, a table with: id of point; X, Y and Z coordinates; 
photos; tightness and angle was obtained. 
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5. ANALYSIS OF METHOD 
This work aims at assessing precision in different areas of 
study by analyzing the precision homogeneity between the 
outside and inside geometry of construction. Therefore, point 
coordinates of the topographic survey and photogrammetrie 
restitution were used in the software AETRA for obtaining 
the adjustment parameter for transformation of similitude 
with stochastic identical point. 
The adjustment parameters between every point set were 
calculated for each area of study. Subsequently, 10 or 12 
points were selected and their coordinates were calculated. 
The standard deviation and vector errors were obtained from 
comparing the topographic and calculated coordinates. Vector 
errors are shown in Table 1. 
Figure 5: View of project restitution