ashtech Z-Xtreme Parts list manual

Z-Xtreme GPS Receiver
System Guide for Post-Process Surveying
Magellan Corporation
Ashtech Precision Products
471 El Camino Real
Santa Clara CA 95050-4300
Phone and Fax Numbers
•Main
• Voice: 408-615-5100
• Fax: [phone]
•Sales
• US: 800-922-2401
• International: 408-615-3970
• Fax: [phone]
• Europe
• Voice: 44-0118-931-9600
• Fax: [phone]
• Support
• US: 800-229-2400
• International: 408-615-3980
• Fax: [phone]
• Internet
• [email protected]
• http://www.ashtech.com
• http://www.magellangps.com

ii Z-Xtreme Operations and Reference Manual
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Part Number: 630045-01 Revision A
November, 2000
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Z-Xtreme, Instant RTK, Z-Tracking, and the Ashtech logo are trademarks of
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iii
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iv Z-Xtreme Operations and Reference Manual
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v
Reliance Fundamentals
Introduction to Post-Process GPS Surveying ................................................. 1
The Global Positioning System (GPS) ................................................................. 2
Surveying with GPS.............................................................................................. 2
Post-process GPS Surveying ............................................................................... 4
Post-process data collection ..............................................................................4
Static data collection....................................................................................... 4
Kinematic data collection................................................................................ 4
Post-process data processing ...........................................................................5
Applications .......................................................................................................... 5
Limitations ............................................................................................................ 6
Ashtech Z-Xtreme Survey System ....................................................................... 6
System Components.......................................................................................... 9
Hardware ...........................................................................................................9
GPS Receiver................................................................................................. 9
Z-xtreme Receiver ....................................................................................... 9
GPS Antenna................................................................................................ 10
Geodetic IV................................................................................................ 11
Choke Ring Antenna ................................................................................. 12
Handheld Computer ..................................................................................... 12
Compaq Aero Pocket PC .......................................................................... 13
Power System .............................................................................................. 13
Internal Power ........................................................................................... 13
External Power .......................................................................................... 14
Software ..........................................................................................................16
Field Application Software ............................................................................ 16
Survey Control CE..................................................................................... 16
Post-Processing Software ............................................................................ 16
Ashtech Solutions...................................................................................... 16
System Hardware Connectivity....................................................................... 19
GPS Receiver – GPS Antenna ........................................................................ 19
Handheld Computer – GPS receiver ............................................................... 20
GPS Receiver – Receiver Power System .......................................................22
Survey Preparation & Execution......................................................................... 25
Overview ..........................................................................................................25
Static Survey ................................................................................................... 27
Kinematic Survey ............................................................................................. 33
Kinematic Initialization .................................................................................. 37
Point Observation ......................................................................................... 40
Contents

vi
Continuous Kinematic................................................................................ 41
Stop&Go Kinematic ................................................................................... 41
Troubleshooting ............................................................................................... 43
GPS receiver does not track satellites ............................................................. 43
1. Is the GPS receiver powered up?............................................................. 44
2. Is the GPS antenna connected to the receiver?....................................... 45
3. A component may be malfunctioning. ...................................................... 45
4. You may have a malfunctioning GPS receiver. ........................................ 46
GPS Receiver Is Not Recording Data ............................................................. 46
1. Is the GPS receiver tracking satellites?.................................................... 46
2. Is the data card installed in the GPS receiver? ........................................ 46
3. Is the data card full? ................................................................................. 46
4. A component may be malfunctioning. ...................................................... 47
Index.................................................................................................................... 49

vii
Figure 2.1 Z-Xtreme GPS Receiver ................................................................. 10
Figure 2.2 Geodetic IV Antenna without and with Groundplane ...................... 11
Figure 2.3 Choke Ring Antenna....................................................................... 12
Figure 2.4 Compaq Aero Handheld Computer ................................................ 13
Figure 2.5 Typical Internal Power Source........................................................ 14
Figure 2.6 Internal Power Source with External Conversion Kit ...................... 15
Figure 3.1 GPS Antenna Cable with TNC Connectors .................................... 19
Figure 3.2 Cable Connected to Z-Xtreme Receiver & Geodetic IV Antenna ... 20
Figure 3.3 Computer Connection Cable .......................................................... 21
Figure 3.4 Aero Handheld Pouch..................................................................... 22
Figure 3.5 Z-Xtreme Connected to External Power ......................................... 23
Figure 4.1 Kit Bag ............................................................................................ 26
Figure 4.2 Inside View of Kit Bag..................................................................... 27
Figure 4.3 Conventional and Fixed-Height Tripods ......................................... 29
Figure 4.4 Measuring HI (Height of Instrument) of GPS Antenna.................... 30
Figure 4.5 Z-Xtreme Survey System Performing a Static Survey.................... 33
Figure 4.6 Geodetic IV GPS Antenna on Rover Pole ...................................... 34
Figure 4.7 Compaq Aero Handheld Mounted on Rover Pole .......................... 35
Figure 4.8 Rover System Ready to Survey...................................................... 37
List Of Figures

viii

1
Introduction to Post-Process GPS Surveying
Although difficult to believe, it has been nearly 20 years since precise positioning
using the Global Positioning System (GPS) was demonstrated. In a relatively short
time, this capability was put to commercial use with the introduction of the Macrome-
ter V-1000 GPS receiver. Although the Macrometer was unwieldy, temperamental,
and very expensive ($150,000 each), its ability to geodetically position points at an
accuracy of 1-2 parts-per-million of point separation (1mm per 1 kilometer), without
the benefit of line-of-sight between the points, was a tremendous asset. This was the
birth of surveying with GPS.
From its beginning in the early 1980s to the mid 1990s, GPS surveying went through
a tremendous evolution. Equipment become much more affordable, reliable, and
manageable in size and weight. But through this entire period, two important charac-
teristics remained the same; accuracy and the surveying method used to achieve this
accuracy. The method was post-process GPS surveying.
With post-process GPS surveying, data is collected and later processed on a com-
puter to produce the final results, i.e. positions of all points surveyed. This method
can be equated to using a conventional theodolite and EDM to collect a sequence of
angles and distances between points, later computing the coordinates of the surveyed
points.
Until the mid 1990s, post-process was the only method available to determine survey-
grade positions using GPS. A new method was then introduced call Real-Time Kine-
matic (RTK). With the RTK method, point positions are determined immediately dur-
ing data collection. This method can be equated to using a total station to collect a
sequence of angles and distances between points, with the total station computing the
coordinates of these points as the data is collected.
RTK GPS surveying has a number of advantages. The results of your survey are
known immediately. Also, with the ability to determine your position in real-time
comes the ability to stakeout. Balancing the advantages of RTK are some disadvan-
tages. RTK-enabled GPS systems are more expensive, in some cases considerably
so. RTK systems are somewhat more complex, requiring management of a commu-
nication link between GPS receivers. Finally, RTK GPS surveying is slightly less
accurate than post-process.

2 Post-Process GPS Surveying
Even with the introduction of RTK GPS surveying in the mid 1990s, post-process
GPS surveying has continued to be the most popular method of surveying with GPS.
It remains the most accurate and reliable method to survey with GPS.
The Global Positioning System (GPS)
Let’s take a quick look at what makes this all possible, the Global Positioning System
(GPS). GPS consists of three primary components, satellites, ground-based control
and monitoring stations, and receivers.
The control and monitoring stations’ main purpose is to monitor and maintain the sat-
ellites. These stations are invisible to the user. You need know nothing else about
them except that they exist to ensure that the satellites are functioning properly.
Satellites make up the second primary component of GPS. The full satellite constella-
tion is defined as 24 satellites, although at the time of this writing 27 are currently
operational. Each satellite is in an orbit approximately 20,000 km above the earth’s
surface and has an orbital period of slightly less than 12 hours. On board each satel-
lite is a radio transceiver. The transceiver receives information and instructions from
the control station, and transmits information about its identity, location, time, etc.
Each satellite is capable of transmission on two separate frequencies, L1 at 1575.42
MHz and L2 at 1227.60 MHz. While you do not have to be concerned with the control
and monitoring stations, you are required to have knowledge regarding the location,
geometry, and number of satellites available during your data collection. These
important factors dictate the reliability and accuracy of a GPS survey.
GPS receivers receive and store transmissions from the GPS satellites. This is their
primary function, and for some receivers, their only function. In addition to reception
and storage of satellite transmissions, some receivers perform additional functions
such as compute and display receiver position in various datums and grid systems,
output raw data and computed position through serial ports, display satellite availabil-
ity information, etc.
Surveying with GPS
A GPS surveying system consists of at least two GPS receivers. The receivers col-
lect data simultaneously to determine the location of one receiver relative to the
other(s). The positional relationship between the receivers is presented in the form of
a vector, i.e. (delta X, delta Y, delta Z) or (delta N, delta E, delta H) between the
receivers. This is a 3-dimensional relationship. It is analogous to a conventional
observation of (horizontal angle, vertical angle, slope distance). Vectors are pro-
duced between all combinations of GPS receivers used during the survey.

3
Introduction
It’s important to remember that GPS observations result in vectors defining the rela-
tionship between the points observed. That is, a vector is the result of a GPS obser-
vation, not the coordinates of the surveyed points. To determine coordinates of
surveyed points, a set of coordinates must first be supplied for one of the points.
Based on this set of coordinates and the GPS vectors observed for all other points,
coordinates for the other points can be computed. In this manner, coordinates for the
newly surveyed points are determined. Similar to a conventional traverse, your initial
set of coordinates can originate from a known control point incorporated into your sur-
vey. Alternatively, assumed coordinates can used.

4 Post-Process GPS Surveying
Post-process GPS Surveying
Post-process GPS surveying can be broken down into two primary tasks, data col-
lection and data processing. Let’s examine each task in detail.
Post-process data collection
Data collection can be performed using two different methods; static and kinematic.
Following is a description of each method.
Static data collection
As the name implies, static data collection is stationary in nature. The GPS systems
simultaneously collect raw data from all available satellites while remaining stationary
on their respective points. Data collection continues at these locations for an amount
of time dependent upon distance between the receivers, satellite geometry, and
obstruction conditions at the data collection locations (for example, trees or building
blocking some of the sky). When data collection is complete at these specific points,
the GPS systems may move to a new set of points to begin another static data collec-
tion session. In most cases, one GPS system will remain on its current point in order
to link the previous set of points to the new set of points. After data collection is com-
plete, data is downloaded to a computer for post-processing. Processing will com-
pute vectors to determine the position of all points observed.
Static data collection produces the most accurate and reliable results due to the
amount of data collected during each observation. The disadvantage is in productiv-
ity. Long observations at each point reduce the number of points that can be col-
lected in a day.
Kinematic data collection
With kinematic data collection, one of the GPS receivers in the system is designated
as the base and remains stationary throughout the survey. All surveyed points are
determined relative to the base. Once operational, the base system simply collects
and stores raw data from all the available satellites.
The other GPS receiver(s) is designated as the rover. Again, as the name implies,
kinematic data collection is dynamic in nature. The operator of the rover system
moves around the project site collecting data on items of interest. While moving
around the project site, the operator will stop for a short period of time to position a
specific item, such as a manhole. Occupation time of the point can range from 6 sec-
onds to 60 seconds. Once finished, the operator moves on the next point. Also, the
operator can position linear features, such as the centerline of a road, by simply walk-

5
Introduction
ing along the centerline and instructing the rover system to store a position every five
seconds, for example. The result is a trail of points defining the centerline.
To facilitate the mobility required to utilize the kinematic method of data collection, the
rover system is designed to be man-portable, usually carried in a backpack. The user
interfaces with the rover system through a handheld computer/data collector.
While it is obvious that kinematic data collection has the advantage of high productiv-
ity, there are disadvantages. Accuracies are not as good as with static data collection.
In addition, the rover system must maintain lock on GPS satellites as it moves around
the project area. Loss of lock requires the user to return to one of the last successfully
established points for initialization.
Post-process data processing
Post-process GPS surveying requires that collected GPS data be later processed to
obtain results. Processing is accomplished by software included with the system.
Processing normally occurs on a PC back at the office, but can also be performed on
a laptop in the field.
To accomplish the post-processing, data is downloaded from each GPS receiver into
the computer. The processing software utilizes this data to calculate vectors between
all GPS receivers operating simultaneously. The vectors define the 3-dimensional
relationship between the GPS receivers. From these vectors, coordinates are deter-
mined for all points in the project, based on the coordinates of one or more known
points. If the survey included any redundant observations (closed loops, repeat
observations), then a least-squares adjustment can be performed to help identify any
blunders in the data and improve on the final point positions. The capability to per-
form a least-squares adjustment is included with the post-processing software pack-
age.
Applications
Post-process GPS is well suited for most surveying tasks. Systems are being used
today for control establishment, boundary surveys, and mapping applications such as
topographic, planimetric, and as-built surveys. Post-process GPS is also very effi-
cient for volumetric measurements such as stockpiles and gravel pits.
In many cases, a GPS system will be vastly more productive in these types of surveys
than a conventional total station, with the added benefit that a GPS system can be
operated by only one person.

6 Post-Process GPS Surveying
Limitations
GPS surveying systems have limitations that affect their ability to perform some of the
survey tasks discussed above. Being aware of these limitations will ensure success-
ful results from your GPS surveys.
The main limitation is not confined to post-process GPS but is a limitation of the GPS
system in general. As discussed earlier, GPS depends on reception of radio signals
transmitted by satellites approximately 20,000 km from earth. Being of relatively high
frequency and low power, these signals are not very effective at penetrating objects
that may obstruct the line-of-sight between the satellites and the GPS receiver. Virtu-
ally any object that lies in the path between the GPS receiver and the satellites will be
detrimental to the operation of the system. Some objects, such as buildings, can
completely block the satellite signals. Therefore, GPS can not be used indoors. For
the same reason, GPS cannot be used in tunnels or under water. Other objects such
as trees can partially obstruct or reflect/refract the signal, so that reception of GPS
signals is very difficult in a heavily forested area. In some cases, enough signal can
be observed to compute a rough position, but in virtually every case, the signal is not
clean enough to produce centimeter-level positions. Therefore, GPS is not effective
in a forest.
This is not to say that GPS surveying systems can only be used in areas with wide-
open view of the sky. GPS can be used effectively and accurately in partially
obstructed areas. The trick is to be able to observe, at any given time, enough satel-
lites to accurately and reliably compute a position. At any given time and location, 7-
10 GPS satellites may be visible and available for use, although the GPS system
does not require this many satellites to function. Accurate and reliable positions can
be determined with five satellites properly distributed throughout the sky. Therefore,
an obstructed location can be surveyed if at least five satellites can be observed. This
makes GPS use possible along a tree line or against the face of a building, but only if
that location leaves enough of the sky open to allow the system to observe at least
five satellites.
Ashtech Z-Xtreme Survey System
The Z-Xtreme Survey System is Ashtech’s most advanced post-process survey sys-
tem. The system includes all required components to perform post-process GPS sur-
veys. The Z-Xtreme Survey System is built around the Ashtech Z-Xtreme dual-
frequency GPS receiver. Being a dual-frequency receiver (utilizes satellite signals on
both L1 and L2 frequencies), the Z-Xtreme makes your GPS system more versatile
and productive compared to a post-process GPS system based on a single-frequency
GPS receiver. A dual-frequency system requires shorter observation times on point

7
Introduction
for static surveys, requires less time to initialize, less effort to remain initialized during
kinematic surveys, and will maintain the highest level of accuracy even when survey-
ing points separated by 20 kilometers or more. There is no more advanced post-pro-
cess survey system than one based on the Z-Xtreme dual-frequency GPS receiver.

8 Post-Process GPS Surveying

9
System Components
A GPS surveying system is made up of a number of components that, at first glance,
may seem a bit overwhelming. On the contrary, setup of a GPS system is not a com-
plicated task. The trick is understanding the purpose of each component in the sys-
tem and how they relate to each other. With this understanding, connectivity of the
hardware components, and when and how to use the software components, becomes
logical and straight-forward.
Hardware
A GPS surveying system includes a number of hardware components, each with a
specific function. The Z-Xtreme survey system offers options for many of the compo-
nents, each with specific advantages. Choosing the right component will depend on
the users needs and environment in which the system is to be used. In this section,
each of the major components of the Z-Xtreme system is presented. If options exist
for a specific component, each option is discussed.
GPS Receiver
The GPS receiver is the component of the system that processes and stores the sat-
ellite signals. A GPS surveying system requires at least two GPS receivers.
Z-Xtreme Receiver
The Z-Xtreme Survey system is built around the Z-Xtreme dual-frequency GPS
receiver shown in Figure 2.1.

10 Post-Process GPS Surveying
The Z-Xtreme supports an integral battery, removable PC card memory, and optional
internal radio. It is capable of functioning as the base or rover in RTK and post-pro-
cessed surveys. The integrated display and control panel supports the ability to per-
form some survey tasks without a handheld computer. Environmentally, the receiver
meets MIL-STD-810E specifications for wind-driven rain and dust.
GPS Antenna
In order for the GPS receiver to receive satellite signals, it must utilize an antenna.
The GPS receiver antenna is the actual collection point of the satellite signals. It is
also the point for which the position of the rover system is computed. Therefore, to
determine the location of a feature, the GPS receiver antenna must be placed over
this feature. The horizontal position of the feature is determined by the location of the
center of the antenna. The vertical position of the feature is determined by the loca-
tion of the center of the antenna minus the known height of the antenna above the
feature. Each GPS receiver in the system will have one GPS receiver antenna.
The Z-Xtreme system offers a choice between two different GPS receiver antennae
for the base system, the Geodetic IV antenna, and the choke ring antenna. Obstruc-
Figure 2.1 Z-Xtreme GPS Receiver

11
Components
tion conditions will dictate which antenna is appropriate.
Geodetic IV
The Geodetic IV antenna, Figure 2.2, is the standard antenna offered.
The Geodetic IV is small, lightweight, and meets the needs of most users. It is avail-
able with an optional groundplane attachment, which is effective in reducing noise
created by satellite signals reflecting off of nearby obstructions. The technical name
for this noise is multipath. Using the groundplane attachment will reduce the effects of
multipath on the data collected. In order to be effective at reducing the effects of mul-
tipath, the groundplane attachment significantly increases the size and weight of the
antenna. For this reason, the groundplane attachment is not recommended for use
on a kinematic rover. If points for static data collection or placement of a kinematic
base are located in areas where obstructions, such as metal buildings, may cause
Figure 2.2 Geodetic IV Antenna without and with Groundplane

12 Post-Process GPS Surveying
multipath, the groundplane attachment is a recommended option.
Choke Ring Antenna
The choke ring antenna, Figure 2.3, is the ultimate antenna for multipath rejection.
For points located in harsh multipath environments, the choke ring antenna would be
advisable. An example of a harsh multipath environment would be the top of a build-
ing which houses large metal compressors and air conditioning units. These struc-
tures will reflect satellite signals which the antenna may pick up. The choke ring
antenna is designed to function in the most demanding multipath environments.
A significant drawback to the choke-ring antenna is its size and weight, making the
antenna unwieldy for mobile use. For this reason, choke-ring antennas are normally
used only in surveys requiring the highest level of accuracy.
Handheld Computer
A handheld computer is an optional component of the Z-Xtreme Survey System. It
serves as a more advanced interface to the Z-Xtreme GPS receiver. Although the Z-
Xtreme has a built-in interface, it is limited in its capabilities. The handheld computer,
running field application software (discussed below), expands on the receiver inter-
face, providing more control and functionality. If the kinematic data collection method
is intended to be utilized, it is highly recommended that one handheld computer be
Figure 2.3 Choke Ring Antenna