Agriculture Reference
In-Depth Information
80
path 4
path 3
50
path 2
path 1
20
-10
0
20
40
60
80
100
easting in m
Fig. 4.2
Modifi cation of the curvatures of subsequent implement paths. Note the change of curva-
ture between path 1 and 4 on the
right side
of the graph (From Heraud and Lange
2009
, altered)
The geometrical explanation for this is simple: a fl exible horizontal strip that is bent
laterally has a steeper curve on the concave side than on the convex side. The differ-
ences in the respective
radii of curvature
between the concave- and convex side
increase with the width of the strip. Hence if in the fi eld strip by strip are joined, the
radii of curvature of the paths on the concave side get shorter and shorter (Fig.
4.2
).
Finally when the implement cannot follow the sharp bent curve any more, farmers
either have to leave a gap between passes or add a short corrective strip.
Extreme effects of this are generally known when implements are used in a cir-
cuitous manner within a rectangular fi eld with steep, rounded edges. This inevitably
creates crescent-shaped gaps in the corners that are not treated by the machine.
Contrary to this, in
fi xed line guidance
, the fi rst path follows a smooth and math-
ematically predefi ned line, commonly called A-B line. In most cases this predefi ned
pass is a straight line. Yet for fi elds that are center-pivot irrigated, it can be a circle.
All additional trips are defi ned by a given offset distance - multiplied by an integer -
from the fi rst path. Again, the offset distance typically is the operating width of the
implement. But contrary to prior pass guidance, the course of each line is - in a
strict sense - independent of the respective preceding pass. Instead, it is only defi ned
by the A-B line, the offset distance and the integer of the pass number. Therefore,
errors between adjacent lines do not accumulate. Once the passes are recorded, they
can rather precisely be followed again in subsequent operations even if these occur
in later years. This would be possible with prior pass guidance as well, provided all
passes are recorded, however, the errors resulting from curvature problems (see
above) remain in this case.
From this follows that generally fi xed line guidance should be the choice
because it isolates errors. Topography and fi eld shapes, however, often do not allow
an exclusive use of fi xed line guidance. The logical consequence of this situation is
that prior pass guidance is restricted to fi elds or parts of them where fi xed line
