Mar_Apr_PCC_2017_Web

with each other and that means the
communications port and baud rate
need to match. The communications
port (commonly referred to as the
“comport”) is the connection points
within the receiver and the transmitter.
The baud rate is the speed at which the
data moves between the receiver and
transmitter; the input and output of
each needs to match or no communication
occurs. Most of the setup needs
is done directly on the receiver display.
After these parameters have been
set, the base location must be established.
For the most accurate position
the process is started and allowed to
run for 24 hours. After 24 hours all
the positions collected, approximate
86,400 of them, will be averaged for an
error differential. It will automatically
will be sent to the SiteNet 900 to be
broadcast.
The other RTK base that we have
at the Farm of the Future is a cellular
RTK station. This base is part of a
network of RTK bases called SmartNet
that was installed by Leica, a GPS positioning
company. It contains similar
components: a GNSS antenna; a GNSS
receiver, cellular modem instead of a
radio transmitter with cabling and a
power source. The antenna is mounted
on a permanent 12 foot mast instead of
a portable tripod. A coaxial cable connects
the antenna to the receivers to
calculate an error differential. Instead
of a radio transmitting a few miles to a
rover; the cellular modem transfers the
error differential to a networked server
in a remote location along with the
error differentials from base stations
across the US. At the same time, a
tractor or other rover device that needs
a RTK signal uses a cellular modem
to call up the server and provide the
rovers location. This location determines
which of the base station’s error
differential will be sent to the rover.
Users of network RTK units like this
typically pay a yearly fee to access the
correction.
On the rover side we use the RTK
for an autoguidance system, a Trimble
AutoPilot. This system replaces the
tractor’s steering with an AutoPilot
steering wheel. It is controlled by a
FMX1000 display that is getting its location
from an AgGPS 25 receiver that
accepts the RTK differential signal for
one to two inch accuracy. This level of
West Hills College is located in the Pleasant Valley area on the west side of
the California Central Valley. It’s pistachio orchard is shown on the left of this
photo and a newly planted garlic field to the right.
accuracy is needed for several of the
farm activities. First of all listing, the
preparation of the soil bed requires at
least two inch accuracy to maintain
rows. Any operation after listing the
beds such as spraying will also require
the same two inch accuracy since the
tractor will need to follow the wheel
tracks to avoid ruining the beds.
Broadcast spraying normally doesn’t
require two inch accuracy, but this
level of accuracy does reduce overlap
and gaps in the spray pattern that can
be wasted materials or reduced yields.
The other rover we use with students
is a TopConGR3 that accepts
a cellular Sim card. This sim card
provides access to the cellular network
that SmartNet uses and thus to the
SmartNet error differential. Though
the antenna and placement is highly
accurate SmartNet has a lower accuracy
because of the distance and latency
of the signal (rover to server; server
back to rover).
Real time kinematic has value in
providing higher precision for: calculating
positions of objects in the field;
guiding equipment through a field; and
placement of sample locations.
Calculating accurate positions is
required for orchards trees when planting
them. RTK is used by many companies
when planting trees; using those
RTK positions will allow for automated
recordkeeping of individual trees. Another
use is to more accurately manage
irrigation by high accuracy positioning
of valves, flowmeters and pumps.
Guiding equipment through field
with RTK creates rows with straight
lines. Now even though that may seem
like a cosmetic purpose, it does have
some economic value. Straight rows,
first of all, allow tractors to follow the
same track through a field without
damaging the crop and limiting compaction.
It also assures accurate placement
and reducing overlap of chemical
and fertilizer products.
Placement of samples with RTK
allows the highest accuracy possible
for marking the position of pest traps,
tissue samples, soil samples and moisture
sensors. This makes that data and
the resulting analysis more valuable.
Doing precision farming is more
than just applying products at a variable
rate. There are hundreds of uses
for the application of technology by a
grower to be more efficient and economical.
RTK provides the accuracy
and precision for those uses. Availability
of RTK is growing and becoming
more common. It needs to be considered
as a part of precision farming
management.
· · · · PCC
March/April 2017 www.progressivecrop.com Page 27
Photo Credit: Terry Brase