Form line following guidance system

A first form line is defined using two or more terrestrial locations. The first form line may be predefined or may be defined by user during a spraying operation. A second form line is then computed using positioning data obtained while following the first form line and a swathing offset corresponding to the width of a spray pattern. The second form line is updated according to one or more deviations from the computed path. The deviations may correspond to operator inputted corrections which allow for obstacle avoidance, etc. The updating generally occurs by following the second form line as defined by the positioning data and the swathing offset and then deviating from the second form line to accommodate one or more terrain features. New GPS data is collected during these steps of following and deviating from the second form line and new positions are computed from the new GPS data. Finally, the updated second form line is defined using the new positions computed from the new GPS data. A further form line may then be defined using the updated second form line information and the swathing offset. A form line following apparatus may include a vehicle fitted with a GPS receiver configured to receive GPS data and GPS correction information and to compute form line following information therefrom. The form line following apparatus may also include a display device configured to receive and display the form line following information.

FIELD OF THE INVENTION 
The present invention relates to precision farming methodologies and, in 
particular, such methodologies as employ global positioning system (GPS) 
technologies. 
BACKGROUND 
In modern agricultural industries, accuracy is essential. Accurate record 
keeping, automated mapping, and precision farming techniques have all 
become crucial factors in the challenge to improve overall crops yields 
and comply with the ever increasing number of environmental regulations. 
The accurate application of herbicides, pesticides and fertilizers is an 
essential component of modern precision farming methodologies. Whether 
such applications are performed by aerial or terrestrial techniques, 
advanced tools that provide highly accurate navigation and guidance 
information for operators have become a requirement. 
The transfer of global positioning system (GPS) technologies to civilian 
industry has greatly assisted in meeting the challenges presented by 
today's precision agricultural needs. Using GPS systems, accurate and 
highly reliable satellite-based positioning information, which typically 
achieves less than one meter accuracy by utilizing differential GPS 
position corrections transmitted from fixed base stations, is provided to 
operators, for example though moving map displays. Such information allows 
for precise navigation and guidance. Systems utilizing GPS technology have 
been used in the past to assist in the aerial and terrestrial application 
of fertilizers, herbicides and pesticides, etc. However, such systems have 
generally been limited in their capabilities. 
For example, as shown in FIG. 1A, GPS guidance systems which allow 
operators to follow essentially parallel line spraying routes across a 
field have been used. For given field, an operator in a sprayer rig 10 may 
begin a spraying pattern along an initial line 12. At the end of the 
field, or at some point prior to the end of the field, the operator 
generally maneuvers the sprayer rig 10 onto a return path 14. The return 
path 14 is essentially parallel to the initial path 12 and is separated 
from the initial path 12 by distance corresponding to the width of the 
spray pattern. An alternative spraying pattern is shown in FIG. 1B. This 
spraying pattern resembles a race track pattern and again provides 
essentially parallel line spraying patterns. 
Spraying patterns such as those shown in FIGS. 1A and 1B are useful for 
aerial applications and for terrestrial applications involving row crops. 
However, such spraying patterns are not well suited for terrestrial 
spraying applications involving open field crops, for example, wheat, 
barley, etc. Typically, such crops are grown over terrain of varying 
contours and often in fields which present obstacles to straight line 
spraying patterns. What is needed, therefore, is a precision farming 
guidance and/or control system for terrestrial spraying applications which 
may be used in an open field crop environment. 
SUMMARY OF THE INVENTION 
In one embodiment, the present invention provides a method of form line 
following. A first form line is defined using two or more terrestrial 
locations. The first form line may be predefined or may be defined by user 
during spraying operations. A second form line is then computed using 
positioning data obtained while following the first form line and a 
swathing offset corresponding to the width of a spray pattern. The second 
form line is updated according to one or more deviations from its computed 
path. 
The deviations may correspond to operator inputted corrections which allow 
for obstacle avoidance, etc. The updating generally occurs as users follow 
the second form line as defined by the positioning data and the swathing 
offset and then deviate from the second form line to accommodate one or 
more terrain features. New GPS data is collected during these steps of 
following and deviating from the second form line (as computed) and new 
positions are computed from the new GPS data. Finally, the updated second 
form line is redefined using the new positions computed from the new GPS 
data and a further form line may then be defined using the updated second 
form line information and the swathing offset. 
In an alternative embodiment, the present invention provides a form line 
following apparatus which includes a vehicle fitted with a GPS receiver 
configured to receive GPS data and GPS correction information and to 
compute position information therefrom. A processor configured to receive 
the position information and to compute form line following information 
therefrom is also provided. The processor may be part of the GPS receiver 
or it may be a separate unit. The processor is also configured to update 
the form line following information in response to form line deviation 
information. The form line deviation information may come, for example, 
from operator inputted corrections to accommodate various terrain 
features. The form line following apparatus may also include a display 
device configured to receive and display the form line following 
information. The display device may include a moving map display and/or a 
light bar display which allow an operator to follow a computed form line 
path. 
Other features and advantages of the present invention will be recognized 
upon review of the following detailed description wherein reference is 
made to the accompanying drawings.

DETAILED DESCRIPTION 
A form line following guidance system is described. The system may find 
application in crop spraying operations or in other situations (e.g., 
harvesting, ploughing, planting, mining, mineral prospecting, or other 
applications) where real-time correction information must be applied to 
previously computed guidance paths. In one embodiment, a method of form 
line following includes defining a first form line using two or more 
terrestrial locations. A second form line is defined using the positioning 
data and a swathing offset. In general, the swathing offset corresponds to 
the width of a spraying pattern (i.e., a boom width). In other cases, the 
swathing offset takes into account varying elevations which may be 
encountered, for example, when applying fertilizers, etc. over a field 
which includes a hillside or other sloping terrain. The second form line 
is followed and updated according to one or more deviations. The 
deviations may correspond to user inputted corrections to accommodate one 
or more terrain features encountered during the spraying operations. GPS 
data may be collected during the steps of following and deviating from the 
computed second form line path and one or more positions computed 
therefrom. An updated second form line may than be defined using the 
computed positions. 
In an alternative embodiment, a form line following apparatus includes a 
vehicle fitted with a GPS receiver configured to receive GPS data and GPS 
correction information and to compute position information therefrom. A 
processor (which may be part of the GPS receiver or a separate unit) is 
configured to receive the position information and to compute form line 
following information therefrom and is further configured to update the 
form line following information in response to form line deviation 
information. Although the present invention is described with reference to 
these and other exemplary embodiments, upon review of this detailed 
description and the accompanying illustrations it will be apparent to 
those skilled in the art that the present invention is equally applicable 
for use in a variety of other guidance systems which accept operator 
inputted real-time corrections. Accordingly, the embodiments described 
below should be regarded as illustrative only. 
Although the methods and apparatus of the present invention will be 
described with reference to GPS satellites, it will be appreciated that 
the teachings are equally applicable to systems which utilize pseudolites 
or a combination of satellites and pseudolites. Pseudolites are ground 
based transmitters which broadcast a PRN code (similar to a GPS signal) 
modulated on an L-band (or other frequency) carrier signal, generally 
synchronized with GPS time. Each transmitter may be assigned a unique PRN 
code so as to permit identification by a remote receiver. Pseudolites are 
useful in situations where GPS signals from an orbiting satellite might be 
unavailable, such as tunnels, mines, buildings or other enclosed areas. 
The term "satellite", as used herein, is intended to include pseudolites 
or equivalents of pseudolites, and the term GPS signals, as used herein, 
is intended to include GPS-like signals from pseudolites or equivalents of 
pseudolites. 
It will be further appreciated that the methods and apparatus of the 
present invention are equally applicable for use with the GLONASS and 
other satellite-based positioning systems. The GLONASS system differs from 
the GPS system in that the emissions from different satellites are 
differentiated from one another by utilizing slightly different carrier 
frequencies, rather than utilizing different pseudorandom codes. As used 
herein and in the claims which follow, the term GPS should be read as 
indicating the United States Global Positioning System as well as the 
GLONASS system and other satellite- and/or pseudolite-based positioning 
systems. 
In addition, the form line following guidance system described herein may 
be supplemented with non-satellite based guidance systems and 
methodologies, such as inertial navigation systems, distance and gyro 
compass and/or other heading indicator systems, laser range finding and 
bearing indicator systems, etc. The use of such systems to assist in 
terrestrial navigation is well known in the art and will not be described 
further so as not to unnecessarily obscure the present invention. It 
should be recognized that such systems could supplement the GPS-based 
system described in detail below and would be particularly useful, for 
example, in situations where satellite-based positioning signals are 
unavailable (e.g., under foliage, behind hills or buildings, in valleys, 
mines, etc.). 
FIG. 2 illustrates a sprayer rig 30 operating in an agricultural field (or 
other plot of land) 32. Sprayer (or floater) rig 30 is equipped with a 
boom 34 which allows delivery of a variety of crop protection products, 
conventional chemicals and/or liquid fertilizers. Examples of the crop 
protection products may include herbicides, pesticides, etc. The crop 
protection products or other chemicals or fertilizers are generally stored 
in a tank assembly 36 and are delivered through nozzles 38 which are 
present in boom assembly 34. Various controls in the cab of sprayer rig 30 
allow an operator to control the flow of chemicals in tank assembly 36 
through boom 34 and nozzles 38, thus allowing the operator to apply such 
chemicals where needed. 
Field 32 may be any one of a number of growing fields. Preferably, field 32 
is an open field, i.e., not one configured for row crops. As such, field 
32 may include growing crops such as wheat, barley, etc. As shown, field 
32 has various contours and may be defined by irregular boundary lines. 
Field 32 also includes a number of terrain features or obstacles such as 
rocks or boulders 40 and trees 42. Other obstacles such as ponds, streams, 
buildings, roads, etc. (not shown) may also be present. During spraying 
operations, sprayer rig 30 must avoid these obstacles and yet still 
deliver the crop protection products and/or other chemicals where needed. 
To accomplish this task, sprayer rig 30 is fitted with a GPS antenna 44 
which receives GPS data from one or more GPS satellites 46. Sprayer rig 30 
will also include a GPS receiver capable of interpreting the GPS data 
received through antenna 44 so as to provide guidance information. The 
guidance system employed by sprayer rig 30 is unlike the guidance systems 
of the prior art because, as those skilled in the art will appreciate, the 
parallel line guidance patterns available from the guidance systems of the 
prior art are unsuitable for use in field 32 where obstacles such as rocks 
40 and trees 42 prevent sprayer rig 30 from following precise parallel 
line swathing (or spraying) patterns. 
FIG. 3 illustrates an overhead view of field 32. Sprayer rig 30 is shown in 
proximity to a rock 40 within field 32. As shown by the guidance path 
information presented as guidance path 50, sprayer rig 30 must follow a 
spraying path through field 32 which accommodates not only the contours of 
the field but also the various terrain features and obstacles presented 
therein. For example, sprayer rig 30 must avoid the rocks 40 and trees 42 
and yet still follow a path 50 which allows for precise application of the 
various chemicals through boom assembly 34. The various form lines 52, 54, 
56, etc. of guidance path 50 are separated by approximately the effective 
spraying width of boom assembly 34. The offset is sometimes referred to as 
a swathing offset and ensures that all areas of field 32 are adequately 
(but not overly) covered by the spraying assembly as the chemicals are 
being applied. 
Notice that guidance path 50 will be such as to accommodate operator 
inputted corrections for deviations around obstacles such as rocks 40 and 
trees 42. That is, after the first form line 52 is traversed by sprayer 
rig 30, a return path (form line 54) is computed which allows for an 
offset by approximately the width boom assembly 34. However, at various 
points along form line 54, operator inputted corrections, such as those 
required to deviate around rock 40, will be input (e.g., through a 
steering wheel). Thus, when computing the next form line (form line 56), 
these operator inputted deviations must be accounted for. The manner in 
which this is accomplished by the present invention is described below. 
FIG. 4 illustrates the basic features of a form line following apparatus 
according to one embodiment of the present invention. FIG. 4 is drawn from 
the stand point of an operator console within sprayer rig 30. However, it 
will be appreciated that other embodiments with varying configurations may 
also be used. 
The form line following apparatus includes a GPS antenna 44 which is 
mounted on sprayer rig 30 so as to have a clear view of the sky. This will 
ensure that antenna 44 is capable of capturing signals from GPS satellites 
46. Signals from antenna 44 are provided to GPS receiver 60 which may be 
mounted inside the cab of sprayer rig 30 or at another convenient location 
on the vehicle. Receiver 60 may also receive differential GPS correction 
information through antenna 48 from one of a variety of sources. For 
example, such differential GPS (DGPS) correction information may be 
provided by radio telemetry from a GPS base station situated near field 32 
as is common in the GPS arts. Alternatively, GPS receiver 60 may receive 
differential GPS correction information from FM subcarrier broadcasts or 
from other sources (e.g., satellite transmissions as are currently 
available from the John Chance Co. in the US or Racal in the UK). GPS 
receiver 60 uses the GPS data provided through antenna 44 from the GPS 
satellites 46 and the differential GPS information received through 
antenna 48 to compute position information for sprayer rig 30. The 
position information corresponds to the terrestrial location of sprayer 
rig 30 at the time the GPS data is collected. Such position computations 
may occur periodically, for example, several times each second. Using 
differential GPS correction techniques common in the art, submeter 
position accuracy may be obtained. In an alternative embodiment, GPS 
receiver 60 may be configured to operate with real-time kinematic (RTK) 
corrections which provide centimeter level accuracy. In general, however, 
submeter accuracy is sufficient for most precision farming applications. 
The position information computed by GPS receiver 60 is processed and 
provided to display device 62. Display device 62 may include a moving map 
display 64 which allows an operator to determine the precise location of 
sprayer rig 30 with respect to the boundaries of field 32. As illustrated, 
field 32 has some irregular boundaries and the intersection of cross-hairs 
66 and 68 define the position of sprayer rig 30 within field 32. The 
process for generating such moving map display information is well known 
in the art and need not be described further. Also included on display 
device 62 may be a compass rose or heading indicator 70. Heading indicator 
70 generally indicates the direction that sprayer rig 30 is traveling. 
Through the use of moving map display 64 and heading indicator 70, an 
operator is provided with simple and effective information to control 
spraying operations within field 32. 
Also included as part of the form line following apparatus is a 
multi-function light bar 72. The multi-function light bar 72 receives 
guidance information from GPS receiver 60 and provides clear and immediate 
guidance information/commands to an operator of sprayer rig 30 through a 
row of light emitting diodes (LEDs). These LEDs are used to alert an 
operator when sprayer rig 30 has deviated from a computed form line path. 
The sensitively of light bar 72 (i.e., the deviation required before an 
LED will be illuminated to indicate that sprayer rig 30 is straying from 
the computed path) may be operator configured for various types of 
spraying operations and field conditions. In addition, the light bar 72 
may have a text screen (not shown) to display user selected information 
such as the form line number, sprayer rig speed, flow rate, etc. In other 
embodiments, multi-function light bar 72 may be replaced by a liquid 
crystal or other display device configured to provide similar course 
guidance and/or correction information. 
During spraying operations, LED 74 will be lit when sprayer rig 30 is 
following a computed form line path as described below. As sprayer rig 30 
deviates from the computed form line path, offset indicator LEDs 76, 78, 
etc. will be lit to indicate the degree (or distance) of deviation from 
the computed path. Note that LEDs 76, 78, etc. will be lit if sprayer rig 
30 deviates to the right of the computed path and corresponding LEDs on 
the other side of LED 74 will be lit if sprayer rig 30 deviates to the 
left of the computed path. Alternatively, LEDs 76, 78, etc. may be lit to 
indicate that sprayer rig 30 should be steered to the right to get back to 
a computed form line path, etc. The times at which the LEDs will be lit 
may be user configured. For example, LED 76 may be lit when sprayer rig 30 
has deviated by two to three feet from the computed form line. Then, if 
sprayer rig 30 continues to deviate, for example to five feet from the 
computed form line path, LED 78 may be lit. In other situations, LED 76 
may not be lit until a five foot deviation has been recognized. In this 
way, the user is provided with information which allows him or her to 
correct the path of sprayer rig 30 back to that of the computed form line. 
Operator corrections and steering controls are input through steering wheel 
80. The form line following apparatus may be included with a steering 
input option which allows steering commands to be transmitted from a 
steering apparatus 82 to GPS receiver 60. Steering apparatus 82 provides 
information regarding the steering inputs through steering wheel 80 so 
that GPS receiver 60 can be provided with real-time update information 
(e.g., the above-described deviations). Using the various steering 
commands provided through steering input apparatus 82, GPS receiver 60 can 
provide appropriate display information to display device 62 and light bar 
72. In other embodiments, other heading sensors such as a gyro compass or 
flux-gate gyro compass may provide the update information to GPS receiver 
60. For the case where no steering information is used, the form line 
following apparatus may rely on updated position information derived from 
GPS data received from satellites 46 to compute and provide the display 
information. 
FIG. 5 illustrates a general computation scheme which may be utilized by 
GPS receiver 60 (or a separate processor) in accordance with the present 
invention. Form line following process 100 starts at step 102 when an 
operator begins the first form line. From step 102 the process moves to 
step 104 where an operator defines the first form line. This may be done 
as sprayer rig 30 is driven across field 32 using the form line following 
apparatus, including GPS receiver 60, to collect and store position 
information or by down loading a previously computed form line map from 
another source. Such a map may be obtained from a geographical information 
structure (GIS) which also contains information on other aspects of field 
32 as described further below. Alternatively, the information may be 
provided from a stored map, such as may be generated by digitizing an 
aerial photograph of field 32. In general, however, the operator will 
define the first form line by driving across field 32 (or at least over 
that portion of field 32 that is to be sprayed), e.g., following a fence 
line, a crop boundary line or a natural contour in the land, at step 106. 
This process finishes at step 108 when the first form line path has been 
completed. During this process, GPS data is collected at a variety of 
geographic locations at step 110. Then, at step 112, the GPS data 
collection ends when the first form line has been completed. 
FIG. 3 illustrates the process of data collection during the definition of 
the first form line in more detail. Notice that as sprayer rig 30 is 
driven across field 32, the form line following apparatus is activated and 
GPS data is collected at a number of points 200, 204, 206, 208, 210, etc. 
The distance between these GPS data collection points is variable, and 
will typically correspond to submeter distances. The GPS data collected at 
each point is processed along with the differential GPS information (or 
RTK corrections) and a series of terrestrial positions are computed. These 
positions (when linked together, e.g., by a straight or curved line 
approximation) will define the first form line--that is, the path followed 
by sprayer rig 30 as it maneuvered across field 32. In this way, GPS 
receiver 60, or a separate processor, computes a first form line which 
corresponds to the actual path traveled by sprayer rig 30. 
Returning to FIG. 5, if additional form lines are to be sprayed, a decision 
made at step 114, GPS receiver 60 (or the separate processor) computes a 
new form line (or swath) to be followed, based on the GPS data collected 
while sprayer rig 30 traversed across the first form line path. An offset 
due to, for example, the effective spraying width of boom assembly 34 is 
also taken into account so that portions of field 32 are not sprayed a 
second time. The computed new form line may be used to generate guidance 
information for the operator of sprayer rig 30. For example, as the 
operator turns sprayer rig 30 around to follow a return path across field 
32, the actual position of sprayer rig 30 (as determined by new GPS 
position information received by GPS receiver 60) is compared with its 
expected position (i.e., the second form line information computed as 
described above). If the actual position agrees with the expected 
position, the operator is so advised, e.g., by the illumination of LED 74 
in light bar 72. This continues as sprayer rig 30 is driven back across 
field 32 with new GPS data being constantly collected and the actual 
position of sprayer rig 30 being constantly checked against its expected 
position. As deviations from the expected positions are noted, display 
information is provided to the operator to allow guidance corrections as 
discussed above. 
This process is further illustrated in FIG. 5 where, at step 118, the 
operator begins the next form line. In general, the operator follows the 
guidance information computed by GPS receiver 60 and displayed on moving 
map display 64 and heading indicator 70 and also on light bar 72. During 
this time, the operator may input corrections for obstacle avoidance or 
terrain features using steering wheel 80 or another steering control. 
Ultimately, the operator will finish the second form line at step 122. 
During the process of following the guidance information provided by GPS 
receiver 60, new GPS data is collected at step 124. The new GPS data will 
be used to provide guidance information as described above and will also 
form the basis for computing any subsequent form line as was the case 
where the GPS data collected while following first form line was used to 
compute the second form line. GPS data collection for the second form line 
ends at step 126. Notice that the subsequent form line is computed based 
on the actual path traveled by sprayer rig 30 and not just the expected 
path computed after the first form line was completed. Thus, any 
deviations of sprayer rig 30 from the computed second form line, which 
were required due to the presence of rocks, trees, etc., will be reflected 
in the new GPS data and the subsequent form line will take into account 
these corrections. 
If a subsequent form line is to be sprayed, a decision made at step 128, 
guidance information for that form line is computed at step 130, with 
offset information being applied as before. These processes continue until 
the spraying operations for field 32 are completed at step 132 at which 
time the form line following process 100 quits at step 134. Notice that a 
decision process at step 132 allows an operator to indicate that a current 
set of form lines have been completed but that the complete set of 
operations for the field have not been completed. This situation may 
arise, for example, where different crops are situated in the same field 
or where a new chemical is being applied. In such cases, the operator may 
indicate that a new set of form lines (corresponding to the new 
conditions) should be initiated, beginning at step 102. 
In some cases, form line following process 100 may be configured so that 
only deviations greater than a specified distance from an intended track 
are recognized. That is, only significant deviations from a computed form 
line guidance path (e.g., the second form line discussed above) will be 
used as decision points for displaying guidance correction information to 
the user. To illustrate, consider the situation illustrated in FIG. 6. As 
shown, a sprayer rig operating in a field 150 was supplied with guidance 
information (e.g., using the above described form line following process 
100 ) that would have the sprayer rig follow an intended path 152. 
However, while traversing field 150, the sprayer rig actually followed a 
path 154. Path 154 is somewhat different than the intended path 152 and 
includes a deviation 156 around obstacle 158. 
It will be appreciated that, in accordance with form line following process 
100, GPS data is collected while the sprayer rig is traversing path 154. 
Therefore, GPS receiver 60 may perform numerous computations that indicate 
that the sprayer rig is not following the intended form line path 152. 
However, where these deviations are not significant, it would be 
burdensome, both in terms of computation operations and in terms of 
operator fatigue, to constantly display guidance correction information to 
the user. In other words, if guidance correction information (e.g., 
illumination of various LEDs of light bar 72) were constantly displayed to 
the user even when the deviations of the sprayer rig from a intended path 
were not significant, a user would soon grow weary of constantly having to 
steer the sprayer rig left and right to correct these minor deviations. 
Accordingly, form line following process 100 may be configured so that 
deviations which are not significant are "ignored". That is, when GPS 
receiver 60 recognizes that the sprayer rig has only deviated from the 
intended form line path by a distance less than a specified distance, no 
new guidance information is displayed (e.g., LED 74 will be lit as if the 
sprayer rig was still on the intended path). Then, when a significant 
deviation, such as deviation 156, is recognized, appropriate guidance 
information which will allow the operator to regain the intended path will 
be displayed. 
As illustrated in FIG. 6, the predefined distance which will trigger the 
display of guidance information essentially "broadens" the width of the 
intended form line path 152 to a "lane". The lane width may be user 
configurable and will typically correspond to a few feet, depending on 
field conditions. As significant deviations are recognized, appropriate 
guidance information is displayed. The guidance information may be 
displayed before the operator veers outside of a lane so that excessive 
"zig-zagging" will be avoided. Thus, the risk of producing cumulative 
errors over several form lines is reduced and the intended paths of the 
sprayer rig through the field remain relatively straight. These factors 
all contribute towards reducing the operator's steering burden and 
operator fatigue. 
Notice also in FIG. 6 that the next intended form line 160 is computed 
based on the actual path 156 traversed by the sprayer rig. Thus, the 
deviation around obstacle 158 is accounted for. Likewise, the third 
intended form line path 162 will be computed based on the actual path 164 
driven by the sprayer rig. 
As indicated above, form line following information may also be provided by 
an external source. FIG. 7 shows illustrative data layers which may be 
provided in a geographic information system (GIS). A GIS is a system of 
hardware, software and geographic data designed to support the capture, 
management, manipulation, analysis, modeling and display of spatially 
referenced data for solving complex planning and management problems. The 
main propose of a GIS can be to find solutions to problems by using both 
geographic and tabular data. For the example shown, GIS 200 (which may 
exist inside a computer system) includes information relating to various 
soils, ownership (e.g., fence lines), roads, streams, elevation, fields, 
and other data, all of which may be overlaid on a base map of field 32. 
The spraying information provided by GPS receiver 60 in the course of 
computing various form lines may also be provided as a layer in GIS 200. 
In this way, a user will have information regarding the application of the 
various chemicals at points of interest on field 32. This may assist a 
farmer in various precision agricultural operations by comparing which 
spray formulas achieved better crop yields. Alternatively, the form line 
information from previous spraying operations may be downloaded for use in 
new spraying operations by providing guidance information as described 
above. 
Up to this point it has been assumed that the field in which the sprayer 
rig operates is relatively flat. However, in those situations where the 
sprayer rig will operate over sloping terrain, certain corrections must be 
accounted for. In particular, it will be appreciated that when the sprayer 
rig is operating on a hillside or other sloping terrain, the boom assembly 
34 will have an effectively shorter horizontal spraying (or swath) width 
than it would have when the sprayer rig operates on essentially flat 
terrain. Indeed, the effective horizontal spraying width of the boom 
assembly 34 may be approximately equal to the physical length of the boom 
assembly multiplied by the cosine of the angle of the slope of the terrain 
(assuming the spraying nozzles do not direct chemicals significantly 
beyond the ends of the boom assembly 34). That is, 
EQU effective horizontal swath width=physical swath width.multidot.cos .O 
slashed., where .O slashed.=slope of the terrain. 
This situation is illustrated in FIG. 8A which shows a first form line path 
250 over a hillside 252. During spraying operations, a sprayer rig 
traveled along the first form line 250 and reached a position 254 defined 
by coordinates x.sub.1, y.sub.1, z.sub.1. Now on the return path, the 
sprayer rig needs to be guided to a position 256 which is offset from 
position 254 by the effective spraying swath distance. Position 256 is 
defined by coordinates x.sub.2, y.sub.2, z.sub.2 and, assuming that 
y.sub.1 .apprxeq.y.sub.2, then 
##EQU1## 
GPS receiver 60 will have computed x.sub.1 and z.sub.1 while the sprayer 
rig was traveling along form line 250. Further, positions x.sub.2 and 
Z.sub.2 will be computed from GPS data received while the sprayer rig is 
traveling along the second form line 260. It will be appreciated that by 
the time the sprayer rig reaches position 256 and computes x.sub.2 and 
z.sub.2, the sprayer rig will have already passed position 256. Thus, the 
guidance information will be late. However, because GPS receiver 60 
computes new positioning data several times each second, the distance 
traveled by the sprayer rig will be insignificant. In addition, guidance 
smoothing and predictive filters (e.g., Kalman filters) can be employed to 
reduce the effects of this lag time between the receipt of new GPS data 
and the calculation of guidance information. 
In alternative embodiments, such as that illustrated in FIG. 8B, sprayer 
rig 30 may be equipped with GPS antennas 44 at either end of boom assembly 
34. This would allow GPS receiver 60 to compute the elevations of each end 
of the boom assembly 34 (provided DGPS or RTK corrections are used) and 
thereby derive the slope of the terrain (i.e., the angle .O slashed.). 
This information could then be used to compute the effective horizontal 
swath width as described above, eliminating the need for guidance and 
predictive filters as may be required in a single antenna situation. This 
concept may be expanded to equip sprayer rig 30 with three antennas, two 
on boom assembly 34 and one positioned (for example) on the cab, to allow 
the computation of three elevation parameters. This may be useful for 
undulating terrain where not only horizontal slope (i.e., roll), but also 
longitudinal slope (i.e., pitch) must be accounted for. 
A further embodiment may equip sprayer rig 30 as described in U.S. Pat. No. 
5,268,695 to Dentinger et al. (the "'695 patent"), assigned to the 
Assignee of the present invention. The '695 patent describes methods and 
apparatus for differential phase measurement through antenna multiplexing 
and the entire disclosure is incorporated herein by reference. In one 
embodiment, multiple GPS antennas are connected to a GPS receiver so that 
a carrier signal received by the antennas is time multiplexed through a 
single hardware path to the receiver where a reference oscillator is used 
to compare the phase of the signal from each antenna to the phase of a 
reference signal. One of the antennas is designated as the reference 
antenna and the carrier signal received by the reference antenna is used 
to phase lock the reference signal generated by the reference oscillator. 
The phase of the same carrier signal received by the other antennas is 
periodically compared to the phase of the reference signal and each 
comparison results in a single phase angle measurement for the respective 
antennas compared to the reference antenna. The computed phase angle 
measurements allow for the calculation of the angle of inclination of a 
plane in which the multiple antennas are situated. Thus, using such a 
system, the angle of inclination of the boom assembly 34 could be computed 
and, hence, the effective horizontal swath distance derived. 
An alternative to the form line following process 100 is illustrated in 
FIG. 9. Sprayer rig 300 is operating in a field and will proceed along 
essentially parallel form lines 302, 310, etc. These form lines may be 
precomputed and will not take into account operator-inputted deviations. 
To avoid over application of chemicals, however, the nozzles of boom 
assembly 304 will be controlled so that the obstacles (and the resulting 
deviations of sprayer rig 300) are accounted for. 
To illustrate, consider that as sprayer rig 300 travels along form line 
302, eight nozzles of boom assembly 304 are operating and, thus, chemicals 
are being applied over a swath path equal to the width of boom assembly 
304 and centered on form line 302. As sprayer rig 300 maneuvers around 
obstacle 306, a form line following apparatus similar to that described 
above recognizes that portions of boom assembly 304 are now positioned 
over areas of the field to be sprayed when sprayer rig 300 is traveling 
along form line 310. That is, portions of boom assembly 304 are 
encroaching on a swath path to be covered during another pass on a 
different form line. Accordingly, the form line following apparatus will 
shut off those nozzles which are positioned outside the swath path 
associated with form line 302 and, thus, this area will not be sprayed 
with chemicals. Instead, the area will be sprayed when sprayer rig 300 
travels along form line 310. 
This operation achieves the same result as form line following process 100 
and also accounts for the deviations around obstacle 306. An alternative 
approach would be to turn off the appropriate nozzles when sprayer rig 300 
travels along form line 310 (assuming all nozzles were operating when the 
swath associated with form line 302 was being sprayed). Other approaches 
utilizing collapsible boom assemblies 34 may also be used. 
To accommodate a process such as that illustrated in FIG. 9, sprayer rig 
300 is fitted with a form line following apparatus similar to that 
described above and a nozzle control device is provided such that nozzle 
control commands from GPS receiver 60 will control the application of 
chemicals. 
In addition to allowing a human operator to steer a spraying rig along 
intended paths, the present invention may be adapted for use with 
semi-autonomous or fully autonomous vehicles which provide some level of 
robotic control. Ground vehicles which make use of GPS technology to 
provide navigation information are now being developed. For example, RAHCO 
International has developed a track mounted, unmanned ground vehicle for 
hazardous waste transport. A description of the vehicle and its navigation 
and obstacle avoidance system is provided in a paper by Raymond C. Daigh, 
entitled "High Reliability Navigation for Autonomous Vehicles" delivered 
and published as part of the 1996 Trimble Surveying & Mapping User's 
Conference User Application Papers. This entire disclosure is incorporated 
herein by reference. Briefly, the vehicle incorporates a dead reckoning 
system which includes a rate gyro, an electronic compass and track 
encoders (the vehicle uses tracks instead of wheels) along with a 
differential GPS positioning system. This system allows for real time 
positioning and navigation at moderate speeds. Those skilled in the art 
will appreciate that systems employing more sophisticated RTK systems 
(which provide centimeter level accuracy and low latency updates) may 
allow for operations at higher speeds. 
In addition to the above-described navigation system, the vehicle developed 
by RAHCO International includes a collision avoidance system. The 
collision avoidance system includes an array of ultrasonic sensors mounted 
on each end of the vehicle and arranged to provide overlapping coverage. 
Although not discussed by Mr. Daigh, other sensors such as radar, laser 
range finding equipment and robotic vision systems could also be used for 
such a collision avoidance system. 
Those skilled in the art will recognize, in light of the above disclosure, 
that a robotic vehicle such as that described by Mr. Daigh could be 
enhanced by incorporating a form line following system similar to the 
present invention. In general, such an autonomous vehicle would be 
provided with a navigation and collision avoidance system such as that 
developed by RAHCO International and would also include the form line 
following methods and apparatus of the present invention. The vehicle 
navigation system would be provided with form line following information 
as described above which, in conjunction with the inertial navigation and 
DGPS equipment could be used to guide the vehicle in a field or other 
environment. Obstacles detected by the collision avoidance system would be 
steered around (by the use of steering output commands provided by the 
steering avoidance system and new GPS data would be collected during these 
deviations. This new GPS data would be used to compute updated form lines 
as described above and this information could be provided as steering 
inputs to the vehicle's navigation system. Of course, in some cases the 
features of a fully autonomous vehicle could be combined with the guidance 
equipment (e.g., a multi-function light bar) associated with human 
operator controlled equipment to provide a semi-autonomous vehicle. 
Thus, a form line following guidance system has been described. Although 
described with reference to specifically illustrated embodiments, the 
present invention has application to a variety of other guidance system. 
Accordingly, the present invention should be limited only by the claims 
which follow.