Agriculture Reference
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RTK-GPS measurement, once
25
RTK-GPS- plus inertial measurement, once
20
RTK-GPS measurements, four times
15
10
5
0
stop and go
3.2 - 4.8 km/ h
6.4 - 9.7 km/ h
12.9 - 16.1 km/ h
speed range
Fig. 5.1 Standard deviation of error when recording digital elevation models (From Westphalen
et al. 2004 , altered)
Abd Aziz et al. ( 2009 ) concluded that from each field operation the intermediate
results of the subsequent krigings (see Sect. 2.4 ) can provide an indication for the
weighing of the data. The kriging - if it occurs for blocks or grid elements - is
associated with a variance of the respective data per run within each grid element.
This implies that several data per block or grid element accumulate. The smaller
the variance of the data within a grid element is, the better the respective elevation
estimate is supported by the measured data and vice versa . Consequently, the aver-
aging function weighted the elevation estimate based on the variance within the
respective grid element. For details to this see Abd Aziz et al. ( 2009 ).
This processing of the data by weighted averaging instead of simple averaging
reduces the errors in digital elevation models (DEMs), especially when a higher num-
ber of surveys is combined (Fig. 5.2 ). Since such topographic elevation maps can be
generated as a byproduct, including a higher number of surveys hardly affects the costs.
Among the various methods that principally are available for generating digital
elevation models or topographic maps, RTK-GPS georeferencing can be regarded
as a favourite, possibly in combination with inertial georeferencing. This technol-
ogy is needed anyway for guidance- or control purposes in precision farming. So
investments on additional hardware are not needed, solely adequate software must
be obtained. This procedure makes it possible to get digital elevation models and
maps that precisely have the resolution and layout that fits to individual fields. These
digital elevation models or maps can be used for several decades, since the topogra-
phy of fields hardly changes over time.
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