It has been proved in practice that compared to standard geodetic procedures close range photogrammetry has its significant advantages in this area. Using standard geodetic procedures (e.g., the polar or orthogonal method) the surveying is very difficult and inefficient. With regard to the fact that there is often very busy traffic near the surveyed buildings the tendency is to minimise the work in the field and the use of close range photogrammetry allows transferring of the majority of work tasks to a photogrammetric working place. During plotting it is easier to establish certain tiny details at objects, decorations, curves … and the pictures themselves may serve as documentation as well. The list of advantages may be as follows:
With regard to the above-mentioned facts the close range photogrammetry is widely used in many areas. We may mention for example the following
The first step when implementing an order is terrain reconnaissance and taking photographs of the given object. Photographs of a building are taken in such a way so that stereo-pairs may be created which cover the whole object. For most objects it is necessary to take two strips of pictures; in the case of a higher building, three or more strips may be necessary. Pictures for each stereo pair are taken from different sites – from the left and right side.
Another step is the measuring of control points. A long-range pulse total station is used for this purpose; the accuracy of measuring in this way is up to 1 cm. Unambiguously identifiable points of a façade are selected as control points. These should be evenly distributed so that each stereo pair contains at least 4 control points.
Then preparation and calculation of orientation of each stereo pair is performed. This consists especially in careful placing of measured control points at each stereo pair, which may also be complemented (if necessary) by connecting points. The control and connecting points are used for precise connecting of pictures and their proper positioning in the coordinate system.
Calculation of orientation
Result of calculation
If the control points have been properly entered, the deviations between the calculated and the actual positions are within 3mm. The resolution of pictures depends not only on their quality but also on the length of the base and the distance between the site and the building. With standard projects the resolution ranges from 4mm/pixel to 8mm/pixel. The attainable resulting accuracy of final plotting is then from 2cm for elements placed in the façade plane and from 4cm for elements protruding from the façade plane. We use the program PI-3000 (TOPCON) for the calculation of stereo pairs and subsequent plotting.
The final product then is a 2D or 3D vector graphical image (in formats *.dgn, *.dwg, *.dxf) and various printouts.
In the case of adverse conditions (high buildings, narrow streets) the final plotting may be complemented by aerial survey images. These concern especially mouldings, roof ridges, sky-lights, chimneys and other elements that are not visible from the ground.
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