CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
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Figure 7. Orthoimage at a scale of 1:10
Figure 9. Histogram of luminosity
4.3 Accuracy Evaluation
The geometry of the orthoimage was examined not only
through the location and the relative distances of the control
points, but also in comparison with the already mentioned
grayscale orthoimage of the whole eastern side of the Gate of
Adrianos. The accuracy of this orthoimage, as it was checked
through field measured control points scattered all over the
surface of the facade, was better than 0.8 mm.
i
> i (
(
I i * f
V Í
— iGmm
Figure 8. Residuals
A number of 126 distinctive check points on the surface of the
object in both orthoimages were measured. None of the
residuals was greater than 12 mm and the RMS was equal to 8
mm. Thus, the end-product covers the accuracy needs of a
mean -scale orthoimage (1:20) but it is rather inadequate for
large scale orthoimages (e.g. 1:5 or 1:10). The radiometric
appearance is also unfavourable at large scales, due to low
resolution, which makes the appearance of the pixels rather
disturbing. Nevertheless, the radiometric histogram of
luminosity and the RGB channels is normal (Figure 9).
5. CONCLUSIONS
The experience and the results, obtained from the present work
show that it is rather early to accept the camcorders as the main
image source for high accuracy photogrammetric procedures
and for long-distance objects. The need for higher image
resolution was obvious at all stages of the photogrammetric
procedure: the invalidity of the results of calibration, the
sensibility of the parameters of absolute orientation when using
different control point selection or measurement, and the
problems occurred during the matching. Nevertheless these
devices can be -in geometric and radiometric way- sufficiently
reliable for low accuracy photogrammetric projects or simple
archaeological documentation. Moreover, the development of
the digital camcorders foretells that in the near future
significant developments will appear. Already, videos with
sensors Advanced HAD CCD with resolution higher than 2
Mpixel are available, with market prices cheaper than 2,000-
2,500 Euros. So, we can expect better results for the final vector
or raster photogrammetric products by using a cheap solution
for image acquisition.
In the cases that there is not enough budget for detailed
geometric recording of complicated monuments, the video
recording consists a very good solution for documentation
purposes. It is a cost effective and quick alternative, which has
no demands for special knowledge or preparation for
stereoscopic recording of the objects. In addition, when the
necessary budget is found or if a damage of the monument will
happen due to any natural of human intervention, the recorded
images can be used for metric purposes.
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