SATPS mapping with angle orientation calibrator

Mobile system apparatus for accurately determining the location of a designated object, spaced apart from the apparatus, without having to approach the designated object. The invention uses a Satellite Positioning System (SATPS), such as GPS or GLONASS, to determine the SATPS location of a first reference SATPS station, whose location is known with high accuracy, and of a second mobile SATPS station. The second mobile SATPS station uses two SATPS signal antennas, spaced apart a known distance but arbitrarily oriented. SATPS antennas at the first and second SATPS stations each receive SATPS signals from a plurality of SATPS satellites that can be used to determine the location of each antenna. The location of each SATPS antenna may be determined using differential corrections for the location of the first SATPS station antenna. The locations of the two SATPS signal antennas at the second SATPS station define a baseline for purposes of determination angular orientation. This angular orientation information, plus information provided by angle and range readouts for the designated object from a rangefinder positioned adjacent to the second SATPS station, allows determination of the location of the designated object without requiring use of magnetic field-dependent instruments such as magnetic compasses that may be inaccurate when used adjacent to metal structures or sources of intense electromagnetic fields. Another approach uses triangulation of the designated object location from two or more spaced apart known locations of the second SATPS station and does not require angular orientation information. Information on the location of the designated object can be processed at the second SATPS station, at the first SATPS station, or at any other place that has SATPS signal processing equipment.

FIELD OF THE INVENTION 
This invention relates to portable Satellite Positioning Systems for 
mapping and to methods of computing location offsets for such systems. 
BACKGROUND OF THE INVENTION 
Development of receivers for Satellite Positioning Systems (SATPSs), such 
as Global Positioning System (GPS) receivers, with inaccuracies as small 
as a few centimeters has opened many survey and navigation activities to 
collection of position data using SATPS technology. High accuracy mapping 
using SATPS can be performed in real time, or the data can be 
post-processed. 
An SATPS usually includes, at the minimum; an SATPS antenna that receives 
SATPS signals from a plurality (preferably four or more) SATPS satellites; 
an SATPS receiver/processor that receives and processes these signals from 
the antenna to estimate the present time and/or location of the system; 
and an information storage or output means to store this information, to 
display this information, or to deliver this time/location information to 
another entity for its subsequent use. The system location of the SATPS is 
usually the antenna location. An object to be mapped in a survey may not 
permit the the SATPS antenna to be positioned contiguous to or on top of 
the object. Examples of such objects include utility poles, buildings, 
signs, trees, motorized equipment, animal homes and habitats, and 
communications and radio tower structures. Where an SATPS has associated 
location inaccuracies of no more than a few centimeters, it is pointless 
to position the SATPS antenna several meters from the object to be mapped. 
Some workers in this field have developed portable or semi-portable 
equipment that can be used to assist surveying of a given land parcel, 
although this equipment often requires line-of-sight measurements that are 
inconsistent with mapping of opaque or partly opaque structures such as 
buildings and towers. 
A geodetic survey system using a digital phase meter is disclosed by Jaffe 
in U.S. Pat. No. 3,522,992. The apparatus measures distances and changes 
therein between a transmitter and a receiver, by combining, modulating and 
transmitting two laser beams having different frequencies and measuring 
their corresponding phase difference at the receiver. The modulated 
composite light beam is split by a dichroic mirror, and the phase and 
intensity of each of the two frequency component signals (modulated) is 
analyzed to determine an initial or reference modulated waveform. The 
reference waveform is compared with a subsequently received waveform 
having the same signal frequency to determine any changes in the 
transmitter-to-receiver optical distance or in the refractive index of the 
intervening transmission medium. This apparatus requires transmission of 
two or more light beams along a line of sight, and the apparatus does not 
appear to be portable. 
In U.S. Pat. No. 3,619,499, Petrocelli discloses a surveying system that 
measures small displacements of a light source. The light source is 
attached to a movable body and is monitored by a television camera. The 
video image is approximately centered on an image screen, and most or all 
other ambient light is filtered out from the screen image. The number of 
raster sweeps from the edge of the screen to the edge of the light source 
image is counted so that a small or large movement of the light source is 
monitored as a corresponding displacement of the light source image on the 
screen. 
A guidance system for an earth-working vehicle, such as a tractor, is 
disclosed in U.S. Pat. No. 4,244,123, issued to Lazure et al. A signal 
transmitter, such as a rotating laser beam source, is positioned in a 
field to be worked, and two signal receivers are positioned at fixed, 
spaced apart, longitudinal locations on the vehicle, to distinguish 
changes by the vehicle in two horizontal directions. The receivers 
determine and report on the present location and bearing of the vehicle, 
based on what may be a phase difference of the signals received at the two 
receivers. 
U.S. Pat. No. 4,309,758, issued to Halsall et al, discloses an unmanned 
land vehicle guided by three omni-directional light detectors carried on 
the vehicle. At least two spaced apart light sources must be provided off 
the vehicle, with each detector receiving light from two of the light 
sources. The vehicle bearing and location appear to be determined by 
signal phase differences for light from a common source arriving at the 
different detectors. 
Gates et al, in U.S. Pat. Nos. 4,396,942 and U.S. Pat. No. 5,073,819, 
disclose method and apparatus for a video survey conducted by a television 
camera mounted on a top surface of a truck or other vehicle that moves 
along a road to be surveyed. The displated video image includes an 
electronically activated overlay image that provides a geometric baselines 
and allows actual distances to be estimated and/or video-recorded, using 
perspective views of the road as the truck moves along. 
A guidance and control system for one or more land vehicles is disclosed in 
U.S. Pat. No. 4,647,784, issued to Stephens. Each vehicle generates and 
transmits a light beam that is reflected from each of two or more 
reflectors, each reflector having its own optical code (for example, 
stripes having different light reflectivities) and being oriented to 
reflect and return the light beam to a light detector carried by the 
vehicle. The returned light beams from each beam are analyzed to determine 
the present bearing of the vehicle. 
U.S. Pat. No. 4,671,654, issued to Miyahara et al, discloses automatic 
surveying apparatus for surveying a route, to be used for a tunnel with 
curves therein. A laser beam is received at, and produces a light spot on, 
one or two projection screens. The light spot coordinates on a screen are 
determined by a screen image pick-up. Position and angular deviations from 
a desired route, of a moving target containing the laser light source, can 
be monitored and measured as the target moves along or adjacent to the 
desired route. 
As disclosed by Goyet in U.S. Pat. No. 4,677,555, a rotating laser beam 
defines a reference plane for an earthworking vehicle, such as a 
pipelaying machine. Datum points, defined by several beacons fixed in the 
ground and indicating the pattern (bearing, elevation) to be followed by 
the vehicle, are provided. A microcomputer carried on the vehicle monitors 
the pattern actually followed by the vehicle. 
Kamel et al, in U.S. Pat. Nos. 4,688,092 and U.S. Pat. No. 4,746,976, 
disclose a method for satellite navigation, using image pixels with 
precisely known corresponding latitude and longitude coordinates of a 
portion of a celestial body such as the Earth. A computer receives these 
images and generates a model of the satellite orbit, longitude, latitude 
and altitude as a function of time, with reference to the celestial body. 
A least squares algorithm converts the measurements into best-fit 
coordinates. 
A method of automatically steering a land vehicle, such as a tractor, along 
a selected course in a field is disclosed in U.S. Pat. No. 4,700,301, 
issued to Dyke. A rotating laser beam source and directional light 
detector/processor are mounted on the vehicle, and two or more reflectors 
are positioned at or near the boundary of the field. The laser beam is 
reflected from the reflectors, returns toward the vehicle, and is received 
by the detector/processor, which determines the present location of the 
vehicle and its present bearing. In another alternative, two rotating 
laser beam sources are positioned near the edge of the field, the the 
laser beams emitted by these sources are received by an omni-directional 
light detector carried on the vehicle. 
Use of a rotating laser beam for two-dimensional navigation of a land 
vehicle in a specified region is also disclosed by Boultinghouse et al in 
U.S. Pat. No. 4,796,198. Three or more reflectors, one having a 
distinctive reflectivity, are positioned near the boundary of the region 
reflect the laser beam back to the vehicle, where the reflected beams are 
received by a photoelectric cell and generate signals with associated beam 
arrival directions that allow determination of the present location of the 
vehicle. Distinctive reflection from the one mirror provides an indication 
of the angular position of the laser beam on each rotation. 
U.S. Pat. No. 4,807,131, issued to Clegg, discloses an automated land 
grading system in which the position of a cutting blade is controlled 
automatically to provide controlled shaping of a land region being graded. 
A laser beam is projected in a predetermined pattern across the land 
region, and a laser detector carried on the grading machine receives the 
beam and approximately determines the location of the cutting blade and 
the blade angle and depth appropriate for grading that location in the 
land region. Information on the desired blade angle and depth is stored a 
microprocessor carried on the grading machine and is compared with the 
actual blade angle and depth to correct the blade orientation and 
elevation. 
Olsen et al disclose survey apparatus for collection and processing of 
geophysical signals, using a Global Positioning System (GPS), a GPS base 
station and one or more data acquisition vehicles, in U.S. Pat. No. 
4,814,711. Each vehicle carries geophysical measuring instruments, a GPS 
signal receiver and processor to determine present location, a visual 
display of present location, and radio communication equipment to transmit 
location information to the base station. The base station periodically 
polls and determines the present location of each vehicle, with reference 
to a selected survey course that a vehicle is to follow. The base station 
transmits commands to each vehicle to keep that vehicle on the selected 
course. Each vehicle also transmits results of the geophysical data it has 
measured to the base station for correlation and possible display at the 
base station. This apparatus requires continual tracking, control and 
correction of the course of each vehicle relative to the desired course 
and requires use of non-portable apparatus (a vehicle and its equipment) 
to provide the desired location and data measurements. All such 
measurements are transmitted to, and analyzed by, the stationary base 
station, and the measurements probably are accurate only to within a few 
meters. 
U.S. Pat. Nos. 4,870,422 and U.S. Pat. No. 5,014,066, issued to Counselman, 
disclose method and apparatus for measuring the length of a baseline 
vector between two survey marks on the Earth's surface, using a GPS signal 
antenna, receiver and processor located at each mark to determine the 
location of at mark (accurate to within a few meters). The location data 
are determined using GPS carrier phase measurements at each survey mark 
and are transmitted to a base station for analysis to determine the 
baseline vector length between the two marks. This approach requires use 
of two spaced apart survey marks and a base station. Use of GPS signals 
from five or more GPS satellites and use of a surveying time interval of 
length .DELTA.t.gtoreq.5000 seconds are required in order to reduce the 
mark location inaccuracies to a less than a centimeter. 
Paramythioti et al, in U.S. Pat. No. 4,873,449, disclose method and 
apparatus for three-dimensional surveying, using triangulation and a laser 
beam that propagates along the perimeter of a triangle. A rotatable 
mirror, a component of the scene to be surveyed, and a light-sensing means 
are located at the three vertices of the triangle, and knowledge of the 
angles of orientation of the rotatable mirror and the camera allow 
determination of the location of the component of the scene presently 
being surveyed. Three fixed, spaced apart stations, including one station 
at the scene to be surveyed, and receipt of a line-of-sight light beam are 
required here. 
Apparatus for determining compass headings, using two GPS antennas located 
at fixed positions aboard a ship or aircraft, is disclosed in U.S. Pat. 
No. 4,881,080, issued to Jablonski. The absolute positions of the GPS 
antennas, with the usual inaccuracies, are measured without use of 
differential GPS. A GPS receiver/processor receives the signals sensed by 
the GPS antennas and determines a compass heading of the ship or aircraft, 
based upon the known relative positions of the two antennas on the ship or 
aircraft. A similar configuration, applied to mapping of ocean currents 
from an aircraft, is disclosed by Young in U.S. Pat. No. 4,990,922. 
Use of three or more GPS antennas, arranged in a collinear or non-collinear 
array on a body, to determine the attitude or angular position of the 
body, is disclosed by Hwang in U.S. Pat. No. 5,021,792 and by Timothy in 
U.S. Pat. No. 5,101,356. 
Gaer, in U.S. Pat. No. 4,924,448, discloses survey apparatus and method for 
mapping a portion of an ocean bottom. Two ships, each equipped with 
identical GPS signal antennas, receivers and processors, move along two 
parallel routes a fixed distance apart on the surface of an ocean. Each 
ship takes radio soundings of a small region of the ocean bottom directly 
beneath itself and receives a reflected radio sound from that same region 
that is originally transmitted by the other ship. The depths of the region 
directly beneath each ship, as determined by each of the two radio sound 
waveforms and by the GPS-determined locations of the two ships, are 
determined and compared for purposes of calibration. 
A portable target indicator system, for use in a battlefield, is disclosed 
by Ruszkowski in U.S. Pat. No. 4,949,089. The target locator system 
includes GPS antenna and receiver/processor, a radio transmitter, a laser 
rangefinder and azimuth angle indicator. A rifleman carries the system 
into the battlefield and directs the laser rangefinder at a target. The 
radio transmitter transmits the rifleman's GPD-determined location and the 
offset location of the target relative to the rifleman to another entity, 
such as an aircraft, that has a weapons delivery system to be used against 
the target. 
In U.S. Pat. No. 4,954,833, issued to Evans et al, a method for determining 
the location of a selected and fixed target or site, using a combination 
of GPS signals and the local direction of gravitational force. Geodetic 
azimuth is determined using GPS signals, and the local gravitational force 
vector is used to relate this location to an astronomy azimuth, using a 
fixed coordinate system that is independent of the local coordinate 
system. The target and a reference site are each provided with a GPS 
signal antenna, receiver and processor to determine the local geodetic 
azimuth. 
Evans, in U.S. Pat. No. 5,030,957, discloses a method for simultaneously 
measuring orthometric and geometric heights of a site on the Earth's 
surface. Two or more leveling rods held at fixed, spaced apart locations, 
with a known baseline vector between the rods. Each rod holds a GPS signal 
antenna, receiver and processor that determines a GPS location for each 
rod. The geometric height of the GPS antenna (or of the intersection of 
the rod with the Earth's surface) is determined for each rod, and the 
geometric height difference is determined, using standard GPS measurements 
(accurate to within a few meters). The orthometric height difference for 
each GPS antenna is determined using the measured GPS location of each rod 
and an ellipsoid or geoid that approximates the local shape of the Earth's 
surface. 
Method and apparatus for surveying the length, width, height and local 
slope of a road is disclosed by Gebel in U.S. Pat. No. 5,075,772. A 
sequence of equally spaced optical markers must be positioned along the 
road, and these markers are sensed by two video cameras and/or 
electromagnetic sensors, mounted on a vehicle and directed at the road 
surface, as the vehicle moves along the road. 
A surveying instrument that uses GPS measurements for determining location 
of a terrestrial site that is not necessarily within a line-of-sight of 
the surveyor is disclosed in U.S. Pat. No. 5,077,557, issued to Ingensand. 
The instrument uses a GPS signal antenna, receiver and processor, combined 
with a conventional electro-optical or ultrasonic range finder and a local 
magnetic field vector sensor, at the surveyor's location. The range finder 
is used to determine the distance to a selected mark that is provided with 
a signal reflector to return a signal issued by the range finder to the 
range finder. The magnetic field vector sensor is apparently used to help 
determine the surveyor's location and to determine the angle of 
inclination from the surveyor's location to the selected mark. 
In U.S. Pat. No. 5,146,231, Ghaem et al disclose an electronic direction 
finder that avoids reliance on sensing of terrestrial magnetic fields. The 
apparatus uses a directional antenna and receiver/processor for GPS or 
similar navigation signals received from a GPS satellite, and requires 
(stored) knowledge of the present location of at least one reference GPS 
satellite from which signals are received. The orientation of the finder 
or its housing relative to a line of sight vector from the finder to this 
reference satellite is determined. This orientation is visually displayed 
as a projection on a horizontal plane. Any other direction in this 
horizontal plane can then be determined with reference to this projection 
from a knowledge of the reference satellite location. 
Spradley et al disclose a geodetic survey system using three or more fixed 
GPS base stations in U.S. Pat. No. 5,155,490. The location of each 
non-movable base station is known with high accuracy, and each base 
station has an atomic standard clock and GPS receiver/processor therein to 
determine GPS satellite clock offset and clock drift for each of several 
GPS satellites. A mobile station receives GPS signals and receives 
synchronized radio signals from each of the base stations, in a manner 
analogous to a LORAN system, and determines the present location and 
observation time for the mobile station. 
With the exception of the Riszkowski and Ingensand approaches discussed 
above, none of the approaches discussed above is portable and 
self-contained and allows use in an arbitrary environment. Further, none 
of these approaches allows definition of baselines for the location 
determination equipment as the mapping proceeds. What is needed is a 
portable SATPS survey system that: (1) provides distance and bearing 
measurements from an observation site to an object to be mapped; (2) is 
not affected by the presence of a metallic structure that would severely 
compromise the accuracy of a magnetic compass used at the site; (3) does 
not require that any part of the survey system be positioned adjacent to 
or contiguous to the object; (4) can be applied to opaque, semi-opaque or 
transparent objects; (5) provides location data for an object with 
inaccuracies of at most a few meters; (6) provides one or more baselines 
for determination of object locations as the mapping proceeds; and (7) is 
flexible and can be used in almost any environment where at least a few 
SATPS satellites are visible. 
SUMMARY OF THE INVENTION 
These needs are met by the invention, which provides system apparatus and 
an associated method for accurately determining the location of a 
designated object that is separated by an arbitrary distance from the 
system equipment. The system first determines its own location, using 
differential SATPS signals that can be received and analyzed at two SATPS 
stations, one (reference) station having a known location and the other 
station being mobile or even portable. A vehicle containing the mobile 
SATPS station uses two SATPS antennas, separated by a fixed distance, so 
that a baseline or vector extending between these two antennas can be 
determined. A portable or hand-carried SATPS station may use one SATPS 
antenna or may use two SATPS antennas separated by a fixed distance. Use 
of two SATPS antennas, separated by a fixed distance, provides a baseline 
and baseline direction (e.g., a line passing through the centers of the 
two antennas) that replaces a baseline determined by a magnetic compass, 
where the compass information is suspect because of magnetic perturbations 
introduced by nearby large metal objects. 
The length and angular orientation ("offset information") of a vector 
extending from one or both of the SATPS antennas to the object of interest 
art then determined, using optical, electro-optical, ultrasonic or other 
survey measurement means. The object location is then determined from 
knowledge of the SATPS antenna location and the offset information. The 
object location can be stored in an on-board memory, together with indicia 
identifying the object, or the object location and object indicia can be 
transmitted to a receiver for storage and/or further signal processing. 
The SATPS antennas and associated SATPS equipment can be mounted on a 
movable vehicle or can be carried into the field by a surveyor. An object 
to be mapped need only be visible from the surveyor's position and may be 
positioned at an arbitrary distance from the surveyor's position. 
In one embodiment, the invention uses a Satellite Positioning System 
(SATPS), such as GPS or GLONASS, to determine the SATPS location of a 
first reference SATPS stations, whose location is known with high 
accuracy, and of a second portable and mobile SATPS station. The second 
SATPS station uses two SATPS signal antennas, positioned a fixed distance 
apart, to receive SATPS location determination signals from a plurality of 
SATPS satellites and to provide orientation of these two antennas relative 
to each other. Differential SATPS correction information for the first 
SATPS station may be used to correct the SATPS-determined location of the 
second station. Location determination means, positioned adjacent to the 
second station, visually determines the location of the designated object 
relative to the second station. The second station can be mounted on a 
vehicle, such as a truck or railroad car, or can be carried into and used 
in the field by a surveyor or mapper. Traditional methods of determining 
orientation, such as use of a magnetic compass, can be corrupted by the 
presence of a large metal-like structure, such as a vehicle body, but an 
SATPS is relatively unaffected by the presence of such bodies.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
The subject invention provides a portable survey baseline for performing 
SATPS-assisted surveys in the field. FIG. 1 illustrates one embodiment of 
this invention, in which a vehicle 11, such as a truck or a railroad car, 
carries an SATPS mobile station 13. The mobile station 13 includes first 
and second SATPS antennas 15 and 17, spaced apart a known distance d, that 
receive SATPS signals from four or more SATPS satellites 19, 21, 23 and 
25. These SATPS signals are passed by the antennas 15 and 17 to an SATPS 
receiver/processor 27 that computes an SATPS-determined location of each 
of these antennas. 
The two SATPS antennas 15 and 17 can be used to determine the length d and 
azimuthal angle .phi. (shown in FIG. 2) for the baseline that extends 
between the two antennas. The SATPS receiver/processor 27 can rapidly 
toggle between the two antennas 15 and 17, when necessary, and can 
independently compute a location for each of these antennas. When the 
location of each of these SATPS antennas is independently computed within 
a short time interval, using the same set of SATPS satellites for each 
determination, the (common) SATPS signal errors will be substantially 
identical. The unchanging antenna spacing d can be used to evaluate the 
quality of the determination of the azimuthal angle .phi.. The azimuth 
angle information may be filtered or otherwise smoothed to stabilize or 
otherwise improve this information for subsequent use in determination of 
the azimuthal angle .phi. of the baseline relative to a selected line that 
intersects the baseline. 
An SATPS reference station 29, whose location is known with high accuracy, 
is positioned in the vicinity of the mobile station 13 and also receives 
SATPS signals from the SATPS satellites 19, 21, 23 and 25 through another 
SATPS antenna 31 that is connected to another SATPS receiver/processor 33 
that (1) measures the SATPS-determined pseudorange values at the reference 
station 29, (2) compares these pseudorange values with the known 
pseudorange values for the reference station 29, and (3) computes 
pseudorange corrections for the reference station that are the differences 
between these two sets of values. The reference station 29 has a 
correction signal transmitter 35 that transmits the SATPS pseudorange 
corrections. These pseudorange correction signals are received by a 
correction signal antenna that is connected to the mobile station 
receiver/processor 27. The receiver/processor 27 corrects the 
SATPS-determined location of one or both of the SATPS antennas 15 and 17, 
using the pseudorange correction information received by the correction 
signal antenna 37, in real time, or nearly real time. Using differential 
corrections for the SATPS-determined location coordinates of the antennas 
15 and/or 17, the inaccuracies in these location coordinates can usually 
be reduced to a meter or less, which is acceptable location accuracy for 
mapping. If surveying is being performed, other procedures can be used to 
reduce the location inaccuracy to a few centimeters or less. The mobile 
station 13 can be separated from the reference station 29 by distances up 
to 500 kilometers (km). In practice, this separation distance is likely to 
be no more than 50 km. 
The two SATPS antennas 15 and 17 are positioned at opposite ends of a 
baseline bar or other structure 39 of known, constant length d. 
Preferably, the length d is much greater than the smallest carrier 
wavelength used for the SATPS signals received from the SATPS satellites 
19, 21, 23 and 25. The SATPS signals received by the mobile station 13 at 
the SATPS antennas 15 and 17 and SATPS receiver/processor 27 may be used 
for calibration or for determination of the most probable location of the 
first and second antennas 15 and 17. 
Once the locations of the SATPS antennas 15 and 17 are determined, the 
location of an object 41, spaced apart from and visible from the mobile 
station 13, may be determined. The object 41 is simultaneously viewed by 
one or two angle-measuring and range-measuring ("ARM") devices 43 and 45, 
such as a single radar-type gun 43 that is pointed and fired at the 
object, with the round trip time .DELTA.t.sub.r for the return signal 
determining the range R from the radar-type gun to the object 41. 
Alternatively, one or two coordinated optical, electro-optical or 
ultrasonic devices 43 and 45 can be positioned adjacent to the respective 
antennas 15 and 17, using the known antenna separation distance d, the 
SATPS-determined locations of the antennas 15 and 17, and differential 
corrections for these antennas. If the locations of the SATPS antenna 15 
and/or 17, the azimuthal angels .phi..sub.43 and .phi..sub.45 for each ARM 
device 43 and 45 to the object 41, and the polar angles .theta..sub.43 and 
.theta..sub.45 for each ARM device to the object 41 (illustrated in FIG. 
3) are known, the offset location of the object 41 relative to the mobile 
station 13 can be determined by triangulation or other techniques. 
Optionally, one set of these angles, such as the polar angles 
.theta..sub.43 and .theta..sub.45, may be deleted here. The absolute 
location of the object 41 can then be determined by combining the location 
coordinates of the mobile station 13 and the object 41. Knowledge of 
several parameters allows the location of the object 41 to be determined: 
(1) separation distance d for the two SATPS antennas 15 and 17; (2) 
location coordinates of the SATPS antennas; (3) azimuthal angles and polar 
angles for the line-of-sight from each ARM device 43 and 45 to the object 
41; and (4) offset coordinates for the ARM devices relative to the SATPS 
antennas. 
The SATPS reference station 29, the transmitter/antenna 35 and the 
receiver/antenna 37 shown in FIG. 1 would be used if the SATPS location 
information for the antennas 15 and 17 and for the object 41 are to be 
processed in approximately real time. Such processing can occur at the 
SATPS mobile station receiver/processor 27. 
Alternatively, such processing can occur at the SATPS reference station 
receiver/processor 33, if the transmitter 35 and the receiver 37 are 
exchanged so that the reference station 29 receives the raw or processed 
SATPS location information from the mobile station 13. The SATPS location 
information could be transmitted to the reference station 29 by the 
transmitter as this information is received from or through the SATPS 
receiver/processor 27. 
Alternatively, the survey information (location of objects 41, direction of 
a survey reference line 57 (shown in FIGS. 2, 3 and 4), location of 
location determination means 43/45, etc/.) can be stored in the 
receiver/processor 27 and post-processed together with SATPS location 
information, contemporaneously measured, from a remote SATPS station such 
as 29. In this alternative, the receiver/processor 27 would be provided 
with a memory of adequate size, but provision of a transmitter or receiver 
37 at the mobile station 13 would be unnecessary. 
Using the apparatus illustrated in FIG. 1, the location of an object 41 
that cannot be easily approached, or that is located in a hostile 
environment (such as a building that is on fire or is emitting hazardous 
fluid), can be determined without approaching the object. 
FIG. 2 illustrates use of an ARM device that includes a radar-type gun 46 
to determine the location of the object 41, using timed electromagnetic 
signal emissions with a selected frequency and sensing the time of arrival 
of a return signal that is reflected from the object. The radar gun 46 
measures the range R and the angle coordinates of the object 41 relative 
to the ARM device. The radar gun 46 is rotatably mounted on a module 47 
that measures the azimuthal angle .phi. and the polar angle .theta. of a 
vector V.sub.o (41, 46) extending from the radar gun to the object 41, 
relative to a selected plane PL passing through the radar gun location. 
Alternatively, this plane may pass through another definable point, such 
as a point on the Earth directly below the location of the radar gun 46, 
and the vertical offset of the radar gun relative to this latter point may 
be accounted for in the measurements. The azimuthal angle .phi. and the 
polar angle .theta. for each range measurement made by the radar gun 46 
may be sensed and stored in a memory unit that is coordinated with or 
forms part of the receiver/processor 27; or these angle values may be 
visibly displayed on one or two angle readout panels 48 and 49. The range 
R or vector length .vertline.V.sub.o (41, 46).vertline. from the radar gun 
46 to the object 41 is determined by the relation 
EQU R=c'.DELTA.t.sub.r /2, (1) 
where c' is the signal propagation velocity for an electromagnetic wave in 
the ambient medium for the frequency used by the radar gun and 
.DELTA.t.sub.r is the elapsed time between firing of the radar gun 46 and 
receipt thereat of a return signal reflected from the object 41. Assume 
that the offset Cartesian coordinates of the radar gun 46 relative to a 
selected point 40 (FIG. 1), such as the center of the baseline connected 
the two SATPS antennas 15 and 17, are known to be (.DELTA.x.sub.O, 
.DELTA.y.sub.O, .DELTA.z.sub.O) in whatever local coordinate system is 
used. The offset Cartesian coordinates of the object 41 relative to the 
selected reference point 40 then become 
EQU .DELTA.x=.DELTA.x.sub.o +R cos (.phi.+.phi..sub.0) cos .theta.,(2) 
EQU .DELTA.y=.DELTA.y.sub.o +R sin (.phi.+.phi..sub.0) cos .theta.,(3) 
EQU .DELTA.z=.DELTA.z.sub.o +R sin.theta., (4) 
where .phi..sub.0 is a suitable reference azimuthal angle in the plane PL 
in which the azimuthal angle .phi. is measured. The offset computations 
set forth in Eqs. (2), (3) and (4) apply no matter what ARM device is used 
to determine the relevant angles and range. 
FIG. 3 illustrates another suitable location determination apparatus 51 for 
determination of the aximuthal angel .phi. and/or polar angle .theta. of 
the object 41 and range R to the object relative to the mobile station 13. 
The apparatus 51 includes a plane surface 53 that is approximately 
parallel to the local tangent plane of the Earth's surface at the mobile 
station site. The plane surface 53 has a center 55, a reference line 57 
preferably passing through the center 55, and a plurality of straight 
lines 59a, 59b, 59c, etc. radiating from the center 55 representing 
various azimuthal angles .phi. relative to the reference line 57. Using a 
vertical sighting guide 61 positioned at the center 55, the object 41 (or 
its vertical projection 41h on the local tangent plane) is visually 
sighted or aligned 60i (or 60h). The azimuthal angle .phi. of a 
horizontally oriented vector V.sub.h (41, 61) extending between the 
sighting guide 61 and the vertical projection 41h of the object 41 on a 
local tangent plane is determined and recorded, stored, displayed and/or 
transmitted for subsequent use. If the polar angle .theta. of the object 
41 relative to the mobile station 13 is also needed, this angle can be 
determined using a vector V.sub.o (41, 61) (or V.sub.o (41, 61') for a 
second alignment configuration) lying in the plane defined by a vertical 
sighting guide 61 (or 61') and a vector V.sub.h (41, 61) (or V.sub.h (41, 
61')) and pointing directly at the object 41 or a target portion thereof. 
The polar angle .theta. can be defined as the angle between the vertical 
sighting guide 61 (or the vector V.sub.h (41, 61)) and the vector V.sub.o 
(41, 61), as illustrated. The range R, or vector length .vertline.V.sub.o 
(41, 61).vertline., from sighting guide 61 to object 41 is found by 
standard rangefinding techniques. 
FIG. 4 illustrates another suitable location determination apparatus 71 for 
determination of the azimuthal angle .phi. and/or polar angle .theta. of 
the object 41 and range R to the object relative to the mobile station 13 
in FIG. 1. The apparatus 71 includes a sighting tool 73 (or two adjacent 
sighting tools 73 and 73'), having a sighting center, that provides a view 
of part or all of the object 41 at a center of the sighting tool. The 
target portion of the object 41 is centered in the sighting tool 73, and 
the azimuthal and/or polar angles corresponding to the object are read out 
on one or two angle display meters 75 and 77 that are part of the 
apparatus 71. 
The reference line 57 in FIG. 2 or 3 or 4 may be taken to coincide with the 
direction of the baseline 39 in FIG. 1. In this instance, the 
SATPS-determined location coordinates of the two SATPS antennas 15 and 17 
determine the reference line 57. The reference line 57 need not pass 
through the designated center 55 (or sighting tool 73), if the offset 
distance and the offset direction between the center 55 and the reference 
line 57 are known. 
Alternatively, as illustrated in FIG. 5, the offset distance d.sub.offset 
between the center 55 and the reference line 57, and the distances D15 and 
D17 from the perpendicular foot F to the respective SATPS antennas 15 and 
17, may be known. Relative to a two-dimensional coordinate system (x, y) 
defined by the reference line 57 with origin at the foot F, the offset 
coordinates of the center 55 with respect to these two antennas become 
EQU (.DELTA.x.sub.15, .DELTA.y.sub.15)=(-d.sub.offset, D.sub.15), (5) 
EQU (.DELTA.x.sub.17, .DELTA.y.sub.17)=(-d.sub.offset, D.sub.17), (6) 
EQU D.sub.15 +D.sub.17 =d. (7) 
Any other suitable coordinate system can also be used to express the offset 
coordinates of the center 55 and the SATPS antennas 15 and 17. 
FIG. 1 illustrates an embodiment in which the location determination means 
or ARM devices 43 and/or 45 are mounted on a truck bed or similar site. 
Alternatively, a location determination means 81 can be provided within or 
adjacent to the cab or user-carrying portion 83 of a vehicle 85, 
illustrated in FIG. 6 with the vehicle door removed for clarity. In this 
instance, the apparatus user would stop the vehicle 85 and, without 
leaving the cab 83, would control the location determination means 81 to 
"sight" or obtain a visual fix on the object 41. Preferably, but not 
necessarily, the range R, the azimuthal angle .phi. and the polar angle 
.theta. (measured relative to a selected reference line 57) of a vector 
V.sub.o (41, 81) extending between the location determination means 81 and 
the object 41 would be determined. 
In one embodiment, also illustrated in FIG. 7, the location determination 
means 81 includes a binocular rangefinder 91 having two independently 
operable optical or ultrasound objectives 93 and 95 that are spaced apart 
a known distance A and that are separately operable to bring images of the 
object 41 from the two objectives into coincidence. When these two images 
coincide, the azimuthal angles .phi..sub.93 and .phi..sub.95 associated 
with the orientations of the objectives are read out and used to determine 
the distances d(41, 93) and d(41, 95) from the respective objectives 93 
and 95 to the object 41, according to the relations 
##EQU1## 
where .phi. is the angle between a baseline, such as L1, established by 
the two SATPS antennas and a selected reference line L2 in a horizontal 
plane. The angles .theta..sub.93 and .theta..sub.95 are read out from 
angular measuring devices 101 and 103 that are part of the rangefinder 91. 
One concern here is the accuracy of these angle readout values. 
In an alternative approach, also illustrated in FIG. 7, the angular 
orientations of the two optical objectives 93 and 95 may be slaved 
together so that the aximuthal angles .phi..sub.93 and .phi..sub.95 
satisfy the relation 
EQU .theta..sub.93 =.pi.-.phi..sub.95. (11) 
In this instance, the distance d(41, 97) from the center 97 of the 
rangefinder 91 to the object 41 and the distance d(41, 93)=d(41, 95) are 
determined by the relations 
EQU d(41, 93)=d(41, 95)=(A/2) csc(.phi..sub.95 -.pi./2), (12) 
EQU d(41, 97)=(A/2) tan (.pi.-.phi..sub.95). (13). 
Optionally, the two optical or ultrasound objectives 93 and 95 in the 
rangefinder 91 in FIG. 7 may provided with a horizontal line that extends 
across that objective, with a polar angle readout device 105 and 107, 
respectively, for which a readout parameter .theta..sub.107 =0 corresponds 
to 0.degree. tilt away from the horizon. A tilt by an angle of 
.theta..sub.107 =74 will produce a polar angle readout of this value on 
the readout device 107. The azimuthal angles and/or polar angle may be 
read out manually and/or stored in a memory for subsequent use in 
relations such as Eqs. (1)-(13). 
Optionally, the two mobile unit GPS antennas 15 and 17 in FIG. 1 can be 
aligned so that the baseline 39 that extends between these antennas: (1) 
points directly toward the object 41; or (2) is oriented at a selected 
angle (e.g., 30.degree. or 90.degree.) relative to a horizontal line 
passing through the vertical projection 41h in FIG. 3. In any of the 
embodiments above, the rangefinder can be positioned on the baseline 39 or 
can be displaced from the baseline. 
FIG. 8 illustrates an approach to object location that does not require 
determination of azimuthal or polar angles. A mobile SATPS station 121, 
which may use a single SATPS antenna 123 or more than one such antenna, is 
sequentially positioned at locations 125A and 125B and determines the 
ranges R.sub.A and R.sub.B ; respectively, from a rangefinder 127 to the 
object 41. Here, the user might use a radar-type gun that determines range 
to a signal-reflecting object 41 but need not provide angle orientation 
information for the radar-type gun. Assuming that the object 41 is located 
on the surface of a reference geoid, triangulation using the ranges 
R.sub.A and R.sub.B at the respective locations 125A and 125B yields two 
possible locations, a correct location and a specious location, for the 
object 41. The specious location can be deleted by use of one additional 
information item, such as specification of whether the object lies 
generally north, generally east, generally south or generally west of one 
of the locations 125A or 125B. With the SATPS station positioned at each 
of the locations 125A and 125B, a sequence of objects such as 41 can be 
determined contemporaneously, using this triangulation approach. 
Preferably, the mobile SATPS station 121 would also communicate with a 
reference station, such as 29 in FIG. 1, to utilize differential SATPS 
corrections in determining the locations 125A and 125B with acceptable 
accuracy (preferably to within one meter) at the mobile station 121 or at 
the reference station 29. 
A Satellite Positioning System (SATPS) is a system of satellite signal 
transmitters, with receivers located on the Earth's surface or adjacent to 
the Earth's surface, that transmits information from which an observer's 
present location and/or the time of observation can be determined. Two 
operational systems, each of which qualifies as an SATPS, are the Global 
Positioning System and the Global Orbiting Navigational System. 
The Global Positioning System (GPS) is part of a satellite-based navigation 
system developed by the United States Defense Department under its NAVSTAR 
satellite program. A fully operational GPS includes up to 24 satellites 
approximately uniformly dispersed around six circular orbits with four 
satellites each, the orbits being inclined at an angle of 55.degree. 
relative to the equator and being separated from each other by multiples 
of 60.degree. longitude. The orbits have radii of 26,560 kilometers and 
are approximately circular. The orbits are non-geosynchoronous, with 0.5 
sideral day (11.967 hours) orbital time intervals, so that the satellites 
move with time relative to the Earth below. Theoretically, five or more 
GPS satellites will be visible from most points on the Earth's surface, 
and visual access to three or more such satellites can be used to 
determine an observer's position anywhere on the Earth's surface, 24 hours 
per day. Each satellite carries cesium and/or rubidium atomic clocks to 
provide timing information for the signals transmitted by the satellites. 
Internal clock correction is provided for each satellite clock. 
Each GPS satellite transmits two spread spectrum, L-band carrier signals: 
an L1 signal having a frequency f1=1575.42 MHz and an L2 signal having a 
frequency f2=1227.6 MHz. These two frequencies are integral multiples 
f1=1540 f0 and f2=1200 f0 of a base frequency f0=1.023 MHz. The L1 signal 
from each satellite is binary phase shift key (BPSK) modulated by two 
pseudo-random noise (PRN) codes in phase quadrature, designated as the 
C/A-code and P-code. The L2 signal from each satellite is BPSK modulated 
by only the C/A-code. The L1 signal, modulated by the P-code, can also be 
used here. The nature of these PRN codes is described below. 
One motivation for use of two carrier signals L1 and L2 is to allow partial 
compensation for propagation delay of such a signal through the 
ionosphere, which delay varies approximately as the inverse square of 
signal frequency f(delay.varies. f.sup.-2). This phenomenon is discussed 
by MacDoran in U.S. Pat. No. 4,463,357, which discussion is incorporated 
by reference herein. When transit time delay through the ionosphere is 
determined, a phase delay associated with a given carrier signal can be 
determined. 
Use of the PRN codes allows use of a plurality of GPS satellite signals for 
determining an observer's position and for providing navigation 
information. A signal transmitted by a particular GPS signal is selected 
by generating and matching, or correlating, the PRN code for that 
particular satellite. All PRN codes are known and are generated or stored 
in GPS satellite signal receivers carried by ground observers. A first PRN 
code for each GPS satellite, sometimes referred to as a precision code or 
P-code, is a relatively long, fine-grained code having an associated clock 
or chip rate of 10 f0=10.23 MHz. A second PRN code for each GPS satellite, 
sometimes referred to as a clear/acquisition code or C/A-code, is intended 
to facilitate rapid satellite signal acquisition and hand-over to the 
P-code and is a relatively short, coarser-grained code having a clock or 
chip rate of f0=1.023 MHz. The C/A-code for any GPS satellite has a length 
of 1023 chips or time increments before this code repeats. The full P-code 
has a length of 259 days, with each satellite transmitting a unique 
portion of the full P-code. The portion of P-code used for a given GPS 
satellite has a length of precisely one week (7.000 days) before this code 
portion repeats. Accepted methods for generating the C/A-code and P-code 
are set forth in the document GPS Interface Control Document ICD-GPS-200, 
published by Rockwell International Corporation, Satellite Systems 
Division, Revision A, 26 Sep. 1984, which is incorporated by reference 
herein. 
The GPS satellite bit stream includes navigational information on the 
ephemeris of the transmitting GPS satellite and an almanac for all GPS 
satellites, with parameters providing corrections for ionospheric signal 
propagation delays suitable for single frequency receivers and for an 
offset time between satellite clock time and true GPS time. The 
navigational information is transmitted at a rate of 50 Baud. A useful 
discussion of the GPS and techniques for obtaining position information 
from the satellite signals is found in Tom Logsdon, The NAVSTAR Global 
Positioning System, Van Nostrand Reinhold, New York, 1992, incorporated by 
reference herein. 
An SATPS antenna receives SATPS signals from a plurality (preferably four 
or more) of SATPS satellites and passes these signals to an SATPS signal 
receiver/processor, which (1) identified the SATPS satellite source for 
each SATPS signal, (2) determines the time at which each identified SATPS 
signal arrives at the antenna, and (3) determines the present location of 
the SATPS antenna from this information and from information on the 
ephemerides for each identified SATPS satellite. The SATPS signal antenna 
and signal receiver/processor are part of the user segment of a particular 
SATPS, the Global Positioning System, as discussed by Tom Logsdon, op. 
cit. 
A second configuration for global positioning is the Global Orbiting 
Navigation Satellite System (GLONASS), placed in orbit by the former 
Soviet Union and now maintained by the Russian Republic. GLONASS also uses 
24 satellites, distributed approximately uniformly in three orbital planes 
of eight satellites each. Each orbital plane has a nominal inclination of 
64.8.degree. relative to the equator, and the three orbital planes are 
separated from each other by multiples of 120.degree. longitude. The 
GLONASS circular orbits have smaller radii, about 25,510 kilometers, and a 
satellite period of revolution of 8/17 of a sideral day (11.26 hours). A 
GLONASS satellite and a GPS satellite and a GPS satellite will thus 
complete 17 and 16 revolutions, respectively, around the Earth every 8 
days. The GLONASS system uses two carrier signals L1 and L2 with 
frequencies of f1=(1.602+9 k/16) GHz and f2=(1.246+7 k/16) GHZ, where 
k(=0, 1, 2, . . . 23) is the channel or satellite number. These 
frequencies lie in two bands at 1.597-1.617 GHz (L1) and 1,240-1,260 (GHz 
(L2). The L1 code is modulated by a C/A-code (chip rate=0.511 MHz) and by 
a P-code (chip rate=5.11 MHz). The L2 code is presently modulated only by 
the P-code. The GLONASS satellites also transmit navigational data at at 
rate of 50 Baud. Because the channel frequencies are distinguishable from 
each other, the P-code is the same, and the C/A-code is the same, for each 
satellite. The methods for receiving and analyzing the GLONASS signals are 
similar to the methods used for the GPS signals. 
Reference to a Satellite Positioning System or SATPS herein refers to a 
Global Positioning System, to a Global Orbiting Navigation Satellite 
System, and to any other compatible satellite-based system that provides 
information by which an observer's position and the time of observation 
can be determined, all of which meet the requirements of the present 
invention. 
A Satellite Positioning System (SATPS), such as the Global Positioning 
System (GPS) or the Global Orbiting Navigation Satellite System (GLONASS), 
uses transmission of coded radio signals, with the structure described 
above, from a plurality of Earth-orbiting satellites. A single passive 
receiver of such signals is capable of determining receiver absolute 
position in an Earth-centered, Earth-fixed coordinate reference system 
utilized by the SATPS. 
A configuration of two or more receivers can be used to accurately 
determine the relative positions between the receivers or stations. This 
method, known as differential positioning, is far more accurate than 
absolute positioning, provided that the distances between these stations 
are substantially less than the distances from these stations to the 
satellites, which is the usual case. Differential positioning can be used 
for survey or construction work in the field, providing location 
coordinates and distances that are accurate to within a few centimeters. 
In differential position determination, many of the errors in the SATPS 
that compromise the accuracy of absolute position determination are 
similar in magnitude for stations that are physically close. The effect of 
these errors on the accuracy of differential position determination is 
therefore substantially reduced by a process of partial error 
cancellation.