Geoscience Reference
In-Depth Information
1 Introduction
According to Abdul and Halim (
2001
), there is a difference between precision and
accuracy. Precision is defined as the closeness of the agreement between inde-
pendent test results obtained compared to the mean value. Accuracy is defined as
the closeness of the agreement between the result of a measurement and its true
value. However, both precision and accuracy have an important role for the TLS
measurements. As provided by Schulz (
2007
) in his study regarding typical
applications for TLS with respect to the scanner precision (Fig.
1
), the user needs
to understand which scanner is the best-suited for a specific application according
to scanner precision. The precision can be obtained by referring to manufacturer
specification or by independent testing.
On the other hand Luhmann et al. (
2006
) have discussed the selection of
measurement techniques which can determine the range of accuracy that can be
achieved as illustrated in Fig.
2
. In geomatic jargon, accuracy has become an
important issue especially for applications that require high accuracy (e.g. milli-
metre level) information such as industrial measurement, deformation survey and
reverse engineering.
Figure
2
shows several measurement techniques that are able to provide
accuracy less than millimetre (e.g. interferometry and industrial metrology).
Though the achievable accuracies are adequate the price of the instruments used
are quite expensive. As mentioned in González-Jorge et al. (
2012
), the used of
industrial metrology (e.g. coordinate measuring machines) is not suitable for
economical investments, which led them to evaluate the others measurement
techniques (e.g. photogrammetry and terrestrial laser scanning). Results from their
study have indicated that both evaluated techniques are significant for industrial
measurement.
With the speed and accuracy of TLS, this instrument can be widely used for
many purposes including accurate 3D applications. For instance, TLS has been
utilized by Bokhabrine and Seulin (
2012
) for 3D characterization of hot metallic
shells during industrial forging. In the application, accurate measurements of
dimensional, volume and shape are crucial for controlling and monitoring the
forging process. For another example Timothy et al. (
2010
) implemented TLS
measurement for tunnel deformation survey. Results obtained from their study
have shown that accuracies achieved are within tolerance even in difficult field
conditions for a railway tunnel. Delˇev et al. (
2012
) have employed geodetic
method for fuel tank inspection, which required measurement uncertainty of
1 mm. The capability of TLS to provide dense 3D data has made it applicable in
this high accuracy application to minimizing the interpolation errors between
points surveyed by others high precision geodetic methods.
Similar to other 3D spatial data capture instruments, the results obtained from
TLS can be impaired by errors from different sources. These systematic errors
