us california horizontal geodetic net specifications 1994

7/31/2019 US California Horizontal Geodetic Net Specifications 1994

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California Geodetic Control Committee (CGCC)

http://www.rbf.com/cgcc/csrs-h50.htm

Mr. Gregory A. Helmer, PLS, Chairperson

email: mailto:[email protected]

CALIFORNIA SPATIAL REFERENCE SYSTEM

(HORIZONTAL COMPONENT)

A PROPOSAL

FEBRUARY 1994

Prepared by:

Alvin (Skip) Christensen, PLS

Lawrence R. Fenske, PLS

Kari Launen, PLS


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TABLE OF CONTENTS

ABSTRACT

INTRODUCTION

BACKGROUND Existing Geodetic Control California High-Accuracy Network Crustal Motions in California NGS's Role - Past, Future Calif. Geodetic Control Committee

ISSUESRECOMMENDATION (PROPOSAL)

CSRS RECOMMENDATION DETAILS

Description Establishment Data Publication/Distribution Maintenance Adjustments Continuously Operating GPS Stations Statutes Current Status (1/94) Education

APPENDIX A, "Summary & Status, California Spatial Reference System"

APPENDIX B, "Requested Data Sheet Revisions (i.e., Additions)"


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ABSTRACT

Global Positioning System (GPS) technology and the expanding use of spatial

information for geographic information systems (GISs) and other new uses of

survey data are causing momentous changes in surveying. These changes havecreated a critical need for a new, statewide high-accuracy horizontal geodetic

network for referencing spatial data. The existing network, the National

Geodetic Reference System (NGRS), has served the nation and California well,but currently it is not adequate for the horizontal referencing needs of the 21st

century.

To meet California's long-term spatial referencing needs, it is proposed that a

portion of the existing NGRS be upgraded to establish a new, high-accuracy

horizontal geodetic network consisting of about 1,100 stations. This newnetwork will be the horizontal component of the planned "California Spatial

Reference System" (CSRS) and will be designated as California's official

horizontal reference system for all surveying activities. After December 31,1999, it will be the only legal reference system for California Coordinate System

coordinate values. The proposed CSRS horizontal network is to be established

and maintained through cooperative efforts involving federal, state, and local

agencies, academic/research institutions, private firms, and individuals.

INTRODUCTION

Today, the surveying profession is undergoing tremendous changes; not only in

technology (technically), but also in data usage. The primary causes of these

changes are ...

Advances in positioning technology resulting from the Global PositioningSystem (GPS).

Expanding use of spatial information by new, emerging technologies,many of which are not traditional surveying activities; e.g., fleet

management, vehicle routing, and search and rescue systems.

Budgetary constraints; private and public, at all levels. Increased spatial information needs for resource management,

environmental assessments, infrastructure improvements, crustal motion

and earthquake hazard studies, damage assessments of earthquake and

flood events, Geographic Information Systems (GISs), etc.

These changes are demanding, and will continue to demand, the use of one,

consistent/accurate statewide, horizontal spatial reference system for all

surveying activities. The use of unrelated local datums of varying accuracy

standards and pre-GPS-established horizontal reference networks is rapidlybecoming inadequate (and unnecessary). Evidence of these demands and


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changes are already apparent: (a) various local agencies have, or are

considering, regulations which require recorded surveying documents to be

referenced to a specific network/datum; (b) interest and use of the California

High Precision Geodetic Network (HPGN) is expanding; (c) the Governor's GIS

Task Force has recommended that the California HPGN be used as the"foundation" for all future geographic information production (GIS data); (d) at

the national level, efforts are underway to establish High-Accuracy Reference

Networks as part of a National Spatial Reference System, and (e) an increasingnumber of continuously operating GPS reference stations of geodetic quality are

becoming operational throughout the state, particularly in southern California.

To be effective, a statewide horizontal spatial reference system must meet thefollowing essential criteria.

Be sufficiently precise to meet nearly all horizontal spatial positioningneeds.

Be systematically maintained in a reliably and timely manner. Have accessible, GPS-suitable "in-the-ground" monuments and/or provide

reliable, accurate raw data from continuously operating GPS reference

stations, together with conveniently available current, valid station

information.

Be part of an overall national spatial referencing system.The needs for a clearly-defined and well-maintained horizontal spatial reference

system are especially critical in California where crustal motions are prominent(a factor that is insignificant in most states). Because of crustal motions, it is

impractical to maintain the existing horizontal control networks with over

18,000 stations to GPS accuracy standards. Instead, a small (in number of

stations), well-maintained, high-accuracy network that is suited for GPS surveys

is required.

This document describes the horizontal component of a new "California Spatial

Reference System" and proposes that it be systematically established and

maintained to meet California's horizontal referencing needs of today andthroughout the 21st century. (Note: Another California Geodetic Control

Committee document will address the vertical-position referencing needs.

Possibly, the same stations will serve both horizontal and vertical positioning

needs.)


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BACKGROUND

EXISTING GEODETIC CONTROL:

Currently, the recognized horizontal geodetic control network (system) withinCalifornia is the National Geodetic Reference System (NGRS) which has 18,000

California stations (9,000 of which are first or second order). This nationwide

horizontal control system is the result of many years of effort, dating back to1807, by the National Geodetic Survey (NGS) and its predecessor agencies to

establish, maintain, and improve the national geodetic network. The NGRS,

which was established basically through the use of traditional survey methods(mostly triangulation for horizontal positioning), has served the nation and

California well for many years.

In the 1986, NGS redefined the horizontal datum for the NGRS, replacing the

North American Datum of 1927 (NAD27) with the North American Datum of

1983 (NAD83). When the new datum was established, the entire network alsowas readjusted to improve the horizontal accuracy of the stations. Thus, changes

in station coordinates from NAD27 to NAD83 were caused by both a datum

change and a new adjustment. Although the NAD83 readjustment removed

many of the distortions and errors in the historical NGRS network, this control

network currently remains inadequate (in general) for many GPS surveys and

today's expanding spatial information needs. The reasons are discussed under

"Issues", below.

Note: The NAD83 datum is referenced to the ellipsoid of the Geodetic

Reference System of 1980 (GRS80); whereas, the reference ellipsoid for GPS is

the World Geodetic System of 1984 (WGS84). The two ellipsoids are

effectively the same. (R. B. Langley, GPS World, February 1992; M. C.

Grunthal, GPS World, April 1992; A. Leick, GPS Satellite Surveying, 1990;

C.R. Schwarz, North American Datum of 1983, NOAA Professional Paper NOS

2, December 1989.) For more information, refer to these and other technical

articles/publications.

CALIFORNIA HIGH-ACCURACY NETWORK:

In 1991/92, a high-accuracy (B Order, 1:1,000,000), horizontal geodetic control

network, consisting of 238 stations, was established throughout California by

GPS survey methods. This network is referred to as the "California High-

Precision Geodetic Network" (HPGN). (Similar networks in other states are

often called "High- Accuracy Reference Networks" or HARNs.)

The California Department of Transportation (Caltrans) sponsored (funded) theestablishment of the HPGN. The actual survey efforts were accomplished as a


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cooperative NGS and Caltrans project with assistance from various local

agencies, universities, and private firms. HPGN stations generally are located

along transportation corridors and are spaced about 40 miles apart on a grid-like

network.

The HPGN is not a new datum; the datum remains NAD83. The HPGN is a new

adjustment of the HPGN stations (on NAD83) at the epoch date of the HPGN

surveys. The epoch date represents the mean date of the GPS data collectioneffort and is 1991.35 for the HPGN. The final HPGN adjustment was performed

by NGS and Scripps Institution of Oceanography in 1992. Thus, the adjustment

has a time tag of NAD83(1992). About 100 stations in the HPGN had existingNAD83(1986) coordinates. Coordinate shifts for these stations from

NAD83(1986) to NAD83(1992), which resulted from the high-accuracy GPS

survey, range from zero to 1.3 meters with an average shift of 0.3 meters.NGS is in the process of adjusting the 18,000 historical NGRS stations to the

HPGN.

CRUSTAL MOTIONS IN CALIFORNIA:

For much of California, the earth's surface (crust) is moving in a complicated

manner relative to the other continental states. The crustal motions are caused

primarily by the northwest movement of the Pacific tectonic plate relative to the

North American plate. Two types of motions occur: (a) secular, which is a

relatively constant movement; and (b) episodic, which is the sudden movementcaused by an earthquake.

Fortunately for California surveyors, the earth scientists have been studying

California's crustal motions for a number of years and have developed

considerable knowledge regarding these motions. Schematic maps have been

developed which show the estimated secular crustal motions throughout

California. In some areas, the secular motion exceeds five centimeters per year

(a meter in 20 years). The scientists also have learned that, in general, an

earthquake must exceed a magnitude of six or seven to cause significantepisodic crustal motion. In addition, studies have shown that displacements

caused by earthquakes dissipate relatively quickly as the distance from the

epicenter increases. However, the 7.3 magnitude Landers earthquake in June

1992 displaced nearly all HPGN stations in southern California to some extent.

One HPGN station was displaced nearly two meters by the Landers earthquake.

California GPS surveyors must learn how to "live" with crustal motions; i.e., to

be knowledgeable as to when it is necessary to apply appropriate crustal motion

adjustments and when not, and how to determine these adjustments when

applicable.


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For most local surveys, the effects of crustal motions usually can be ignored

(and in practice, are ignored). But, crustal motions can become an important

consideration when the local survey data is used for other purposes; e.g., the

data is (a) incorporated into geographic information data base, (b) used as

control for another survey, (b) merged with data from another survey, and/or (d)used for current/historical data comparisons. The importance of considering

crustal motions will increase as survey records and data bases mature and new

data is mixed with historical data.In addition, the effects of crustal motions must be considered for high-accuracy

GPS surveys covering large areas or long corridors, especially east/west surveys.

NGS's ROLE - PAST, FUTURE:

Until recently, NGS actively provided all required geodetic control needs for thesurveying profession. Over 285,000 horizontal control stations have been

established nationwide and are included in the NGRS. Data for these stations is

readily available from NGS's National Geodetic Information Center; but, asmentioned previously, the historical NGRS is currently inadequate for the needs

of today and in the future.

Unfortunately, resources at the Federal level are not available to establish and

maintain a new horizontal reference system of sufficient accuracy, density, and

timely availability to fulfill today's GPS surveying and spatial referencing needs.

Thus, NGS is formulating various policies to guide the development of amodern National Spatial Reference System. Key policies, as expressed in the

NGS August 4, 1993, "Mission, Vision, and Goals" document are summarized

below.

NGS will observe, monitor, and maintain a very high-accuracy, multi-dimensional network consisting of monumented stations at a spacing of

approximately 100 kilometers plus additional stations in crustal motion

areas. This network will be the Federal Base Network. Horizontal

positions generally will be B Order with some stations A Order.

NGS will coordinate the cooperative establishment of (and focus data andtechnical support, data processing, and data dissemination activities for) a

very high-accuracy, multi- dimensional network consisting of

monumented stations at a spacing of about 25 to 30 kilometers plus

additional stations in crustal motion areas. This network will be the

Cooperative Base Network. Horizontal positions will be B Order.

NGS will provide, upon written request, quality assurance, archiving, anddistribution functions for contributed surveys, by or for governmental

entities, having station spacings less than 25 kilometers. This network will

be the User Densification Network. Horizontal positions will be First-Order.


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CALIF. GEODETIC CONTROL COMMITTEE:

In late 1992, members of the Advanced Technologies Subcommittee of the

California Land Surveyors Association began to discuss the need to develop

standards and specifications for high-production-type GPS surveys. To initiateaction, the subcommittee held an informal meeting in January 1993 at the annual

California State University, Fresno Surveying Engineering Conference. Various

GPS surveying issues were discussed, including geodetic reference networks. Asa result of this meeting, a second meeting was held in March 1993 to continue

discussions. At the March meeting, the group established a formal California

Geodetic Control Committee (CGCC) consisting of 17 members from variouspublic and private organizations. The Committee includes a broad representation

of California surveyors (GPS experience, organizational size, geographic

location, etc.).

Although the Committee officially is comprised of 17 members, all interested

California surveyors are encouraged to participate in the activities of theCommittee. In fact, a number of other surveyors actively assist the Committee in

developing consensus positions, preparing policy/procedural documents, and

other Committee efforts.

The California Geodetic Control Committee is assigning various tasks (issues)

to specific subcommittees. This document (proposal) is the result of the efforts

by the Horizontal Geodetic Reference System subcommittee.

ISSUES

The critical horizontal spatial referencing issues challenging California's

professional surveyors are as follows:

1. Inadequate Network Accuracy: Although the historical NGRS wasestablished through exemplary survey efforts, most horizontal stations

within the NGRS are of insufficient accuracy for today's GPS survey

methods (except the HPGN stations). Routinely, GPS surveys exceed theaccuracy of the controlling NGRS stations which means high-accuracy

GPS surveys are distorted by adjusting them to less-accurate control.

Also, GPS methods allow baselines to be determined (measured) that

were impossible to determine with historical surveying methods; e.g.,

across mountain ranges. As a result, GPS survey methods detect errors in

horizontal control networks that could not be discovered (or corrected)

prior to GPS.

2. Poor Station Location: The survey methods used to establish the NGRSrequired "lines of sight" between stations; thus, many stations are located


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on mountain peaks, tops of tall buildings, or where towers are required for

use. As a result, numerous NGRS stations are inaccessible and unusable,

or at best, inconvenient to use. In addition, many existing control stations

are unsuited for GPS survey methods because they lack the required

visibility to the sky. At these stations, nearby trees, buildings, or otherstructures block the satellite signals from reaching the GPS receiver

antenna. Other NGRS stations are unsuitable because they are located

near reflective surfaces (e.g., buildings) or transmission lines or towersthat can cause GPS data distortions and multipathing errors. Finally, most

existing NGRS stations were primarily located to meet the survey needs

rather than for convenient public access. Thus, many stations are locatedon private lands which, at times, makes accessibility difficult or

impossible.

3. Limited Network Maintenance: For many years, NGS had an activeprogram to maintain the NGRS stations. However, in recent years, budget

constraints have eliminated these maintenance efforts. This reduced

maintenance effort, together with normal construction activities and otherevents, has resulted in many stations being lost or destroyed. For

California, the accuracy of GPS survey methods has introduced a new

maintenance issue. Crustal motions along the central and southern coast,

and to a lesser extent in other regions, can distort (over time) the

monumented network so that it no longer meets GPS-survey accuracy

capabilities and requirements. (See "Crustal Motions in California",

above, for details.) Currently, comprehensive policies and procedureshave not been developed and published, at either the national or state

level, for maintaining (updating) the existing NGRS for the effects of

crustal motions within California.

4.No Established Crustal Motion Procedures: In addition to a maintenanceissue, California's crustal motions require the development and use of

specific procedures for data publication, coordinate notation, and survey

adjustments. Today, these procedures are not established. Because of

crustal motions, the positions of control stations will change both "in

actual fact" and by published value (the latter, if the network ismaintained properly). Thus, publication and coordinate notation

procedures, such as dating coordinate values, are necessary to (a) ensure a

clear, undisputable understanding of the basis for the information (data)

presented, (b) facilitate the efficient exchange of geographic information

for GISs and other uses, (c) enable the reliable use of data obtained at

different time periods, and (d) accommodate the needs of large and high-

accuracy GPS surveys. The effects of crustal motions create a number of

options for adjusting surveys. To ensure consistency in record data,

procedural guidelines are required; e.g., selection of the surveyadjustment date (epoch).


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5. Reduced NGS Assistance: NGS does not have the resources to establishand maintain a new (modern) horizontal, spatial reference system that

meets the needs for local and regional surveys. Resources at the national

level will be focused on a framework network (station spacing 100

kilometers). The individual states, in cooperation with NGS, are todevelop, establish, and maintain a densified network that meets the needs

of the local surveyor. Refer also to "NGS's Role - Past, Future", above.


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RECOMMENDATION (PROPOSAL)

To meet California's horizontal spatial referencing needs of today and

throughout the 21st century, it is recommended that a California Spatial

Reference System (CSRS) horizontal network, consisting of about 1,100 BOrder or better monumented stations, be developed, established, and maintained,

through cooperative efforts involving NGS, state/local agencies,

academic/research institutions, and the private sector; and that this network bedesignated as California's official, and only, horizontal spatial reference system

for all land surveying activities.

CSRS RECOMMENDATION DETAILS

Important Notice: This section outlines certain NGS responsibilities. Although aconsensus has been developed with NGS on many issues, full concurrence has

not been reached on all issues. This is a proposal.

DESCRIPTION:

(DEFINITION, STANDARDS, SPECIFICATIONS)

Note: Although it is planned that the CSRS will serve both horizontal and

vertical positioning needs, the following is limited to the CSRS horizontal

control component.

1. Name: California Spatial Reference System (CSRS), HorizontalComponent.

2. Definition: The CSRS horizontal competent is a high-accuracy,monumented geodetic spatial-reference network consisting of ...

o The California HPGN (about 240 stations),o HPGN Densification Surveys (about 850 stations), as described in

this document, and

o Other geodetic control stations that meet or exceed therequirements outlined in this document for HPGN Densification

Surveys, and which are included in either the Federal or

Cooperative Base Networks for California as defined by NGS.

3. Status:o Official horizontal spatial reference system for California.o After December 31, 1999, only legal reference system for

California Coordinate System coordinate values.

o Part of the National Geodetic Reference System (NGRS),specifically either the Federal or Cooperative Base Network.

4. Datum: NAD83.


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5. Standards & Specifications (Minimum):o HPGN - B Order, Class I (1:1,000,000); see note below.o HPGN Densification Surveys - B Order, Class II (1:500,000); see

note below. Reference: Federal Geodetic Control Subcommittee

(FGCS) "Geometric Geodetic Accuracy Standards andSpecifications for Using GPS Relative Positioning Techniques".

Note: It is anticipated that the FGCS will establish a 1:500,000

accuracy standard with specifications between First Order(1:100,000) and the current B Order (1:1,000,000).

6. Reference Control Network:o HPGN - Completed; reference control determined by NGS.o HPGN Densification Surveys - The California HPGN.o Other Surveys - As approved by NGS.

7. Survey Method: GPS only.8. Stations: See Appendix A for a tabulation of the HPGN and proposed

HPGN densification stations.o Monumentation: Existing NGRS stations shall be used when the

requirements for stability, durability, and location are met.

Minimum requirements for new monuments are as follows:

HPGN - NGS Class A Rod.HPGN Densification Surveys - NGS Class B Rod.

Note: Alternative means to ensure a permanent station location

(i.e., monumentation) are permissible for continuously operating

GPS reference stations. See subsection below entitled,"Continuously Operating GPS Stations".

o Final Spacing - Varied to meet positioning and crustal motionneeds; average about 20 kilometers (12 miles).

o Location - Station locations shall be secure, accessible, stable, andGPS suitable.


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ESTABLISHMENT:

Since the California HPGN (epoch 1991.35) has been established, the following

is limited to the establishment of the HPGN densification stations. These

stations will be established on a survey-by-survey basis as interest developswithin an area and resources become available.

1. Coordination/Review: The California NGS State Geodetic Advisor shallcoordinate the HPGN densification surveys and perform the required "on

site" NGS reviews. The Advisor also will provide assistance (advice) for

densification surveys.2. Standards, Specifications, Procedures: See "Description", above and

the other applicable subsections in this section, "CSRS Recommendation

Details".3. Who Initiates: Any state/local agency, academic/research institution, or

private firm may initiate a HPGN densification survey.

4. Who Accomplishes: The HPGN densification surveys shall beaccomplished through cooperative efforts involving NGS, state/local

agencies, academic/research institutions, and/or private firms. The field

efforts for the densification surveys shall be performed at the local level

(state/local agencies, academic/research institutions, private firms, and

individual surveyors). Also, see subsection "Adjustments", below.

5. Planning: Prior to planning the station locations, the lead agency/firmshould contact others who are interested in geodetic control and determinetheir interest and support for the proposed densification survey. Contacts

should include various state/local agencies, academic/research

institutions, local professional surveying organizations, earth scientists,

and local geodetic surveyors.

6. NGS Submittal: All HPGN densification surveys (CSRS surveys) shallbe submitted to NGS, in the required format, for inclusion in the National

Geodetic Reference System as part of either the Federal or Cooperative

Base Network.

7. NGS On-Site Reviews: At a minimum, the following on-site reviewsshall be made by the California NGS State Geodetic Advisor for each

HPGN densification survey.

o Prior to constructing the monuments, a review of the networkschematic and observation schedules.

o Prior to submittal of the survey to NGS for final processing, areview of the on-site data quality checks, on-site adjustments,

observation data (log sheets, mark rubbings, raw data files), station

descriptions/recovery, initial required blue-book files, and the

project report.


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o Exceptions to the above reviews are permitted as determined by theCalifornia NGS State Geodetic Advisor.

8. Non-CSRS, High-Accuracy GPS Surveys: Some high- accuracy GPSsurveys will be completed that meet or exceed the requirements for CSRS

horizontal control surveys, but the survey data will not be formatted("blue booked") and submitted to NGS for inclusion in the NGRS (either

the Federal or Cooperative Base Network). For these surveys, the

California Geodetic Control Committee will encourage the surveyor tofile a record of survey so the horizontal control information will be

available for use by other surveyors.

9. References:o Federal Geodetic Control Subcommittee "Geometric Geodetic

Accuracy Standards and Specifications for Using GPS Relative

Positioning Techniques".

o California Department of Transportation (Caltrans) "CA- HPGNDensification Surveys".

DATA PUBLICATION/DISTRIBUTION:

1. Epoch Dates:o When published, shown on a survey document, or included in an

electronic file, coordinate values for the National Geodetic

Reference System (Federal and Cooperative Base Network stations

within California), CSRS, and California Coordinate System shallbe time-dated with an epoch date.

o The epoch date shall be the time (date) the coordinates are valid.See additional details under the subsections "Adjustments" and

"Statutes", below. Previously, NGS time-tagged coordinate values

the year the adjustment was completed (not necessarily the survey

epoch date). NGS has revised their procedures to conform to the

above for California. Thus, coordinate values for surveys within

California that are referenced to geodetic control on the North

American tectonic plate will have an epoch date conforming tomean time when the data collection was performed (see

"Adjustments" below); e.g., the epoch for the Landers earthquake

resurvey is "1992.88".

2. Data Publication and Distribution:o NGS Publication and Distribution: The CSRS will be part of the

National Geodetic Reference System; thus, NGS shall be

responsible for the integrity, publication, and distribution of CSRS

data in the same manner as other NGS data. Data will be available

from NGS's National Geodetic Information Center, Silver Springs,Maryland.


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The California Geodetic Control Committee will encourage NGS to

improve (modernize) their data distribution methods and

procedures by providing recommendations and participating in

cooperative efforts.

oLocal Publication and Distribution: In addition to the NGS datadistribution efforts, the California Geodetic Control Committee will

pursue publication of the CSRS data in hardcopy and electronic-

media forms at the local level for distribution (sale) to Californiasurveyors. To minimize the sale price, the data will be published by

California Coordinate Zones; i.e., six publications. In addition to

the NGS Data Sheets, these publications also will include a "toreach" sketch for each station and a notice identifying the station's

"adopt-the-monument" sponsor (see below, "Maintenance"). It is

anticipated that the local publication and distribution of the CSRSdata will be accomplished through a California professional

surveying organization or a surveying book distributor.

o Data Sheet, Crustal Motion Information: For each CSRS station,the NGS station Data Sheets shall show (i) the current estimated

annual secular motion for the station, (ii) a historical listing of the

station's positional shifts by epoch, and (iii) a historical listing ofthe various determinations of the station's estimated annual secular

motion, by epoch. See Appendix B for suggested details.

o Crustal Motion Map: NGS also shall continue to publish a map thatshows, in a schematic form, the estimated horizontal crustalmotions throughout California. Periodically, the map shall be

revised as data from new surveys become available.

o Crustal Motion Educational Document: The California GeodeticControl Committee will encourage NGS to develop a

comprehensive document which discusses geodetic survey issues

related to crustal motions. See "Education", below.

3. Crustal Motion Computer Program: NGS shall continue to develop,maintain/update, and distribute (sell) to California surveyors a stand-alone

computer program for estimating the effects of crustal motions. Thisprogram, which is named "Horizontal Time Dependent Positioning"

(HTDP), estimates updated coordinate and/or observation values,

horizontal crustal motion velocities, and station displacements. The

HTDP program shall be updated (refined) as data from new surveys

become available. The California Geodetic Control Committee, in

cooperation with NGS, will develop guidelines for using the HTDP

program.


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MAINTENANCE:

1. Coordination: The California NGS State Geodetic Advisor shallcoordinate the CSRS maintenance efforts.

2.

Standards, Specifications, Procedures: All survey efforts related tomaintenance of the CSRS stations shall be performed in accordance with

the standards, specifications, and procedures that were used to originally

establish the given station(s) and the procedures in this section, "CSRSRecommendation Details". Note: Some crustal motion resurveys will

establish new coordinates, having a new epoch, for all stations included in

the resurveys. However, the CSRS goals are to keep the number of epochsis use throughout California, at any one time, to a minimum and also to

avoid statewide readjustments (and thus, new statewide epochs) for as

long as feasible. See policies under "Adjustments", below3. Who Accomplishes: The CSRS maintenance efforts shall be

accomplished through cooperative efforts involving NGS, state/ local

agencies, academic/research institutions, private firms, and individualCalifornia surveyors. See also "Adopt A Monument" program, below.

4. Annual Inspections: Each CSRS station shall be inspected annually anda report made to the California NGS State Geodetic Advisor. This effort

shall be accomplished at the local level (state/local agencies,

academic/research institutions, private firms, and individual surveyors).

The California Geodetic Control Committee will encourage NGS to

develop a user-friendly, computerized recovery note system for reportingstation conditions and, when required, revising station descriptions.

5. Lost or Damaged Stations: Efforts to replace lost or damaged CSRSstations should be initiated and completed as soon as feasible after the

need is discovered. The field effort required to replace lost and damaged

stations shall be accomplished at the local level (state/local agencies,

academic/research institutions, private firms, and individual surveyors).

6. Crustal Motion Resurveys:o Earthquake (Episodic) Resurveys: After each major California-

related earthquake, NGS shall determine, in cooperation with theCalifornia Geodetic Control Committee and California's earth

scientists, the need for a resurvey and, if required, the extent of the

area to be resurveyed. The area of the earthquake resurveys shall

include all HPGN stations that are suspected to be affected by the

earthquake plus one level of HPGN stations beyond the perimeter

of those stations affected. In general, only selected HPGN

densification stations will be included in the earthquake resurvey as

directed by NGS, in consultation with the California Geodetic

Control Committee and California's earth scientist. It is anticipatedthat it will be feasible to reposition most HPGN densification


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stations within an earthquake resurvey area through a readjustment

based on the HPGN resurvey, data from continuously operating

reference GPS stations, an updated HTDP program, and/or advice

from earth scientists.

oAccumulated Secular Motion Resurveys and Adjustments: Overtime, accumulated secular crustal motions will distort the CSRS

network to the extent that it does not meet the required (published)

network standards within a local, regional area. Thus, as required,regional and statewide resurveys and adjustments (each with a new

epoch) shall be performed to eliminate the positioning errors caused

by accumulated secular crustal motion. The determination as towhere and when secular motion resurveys are necessary shall be a

cooperative decision by NGS, the California Geodetic Control

Committee, and California's earth scientists. Note: It is anticipatedthat accumulate secular motion resurveys and adjustments can be

minimize by upgrading the secular motion estimates. See next

subsection.

o Secular Motion Verification Surveys: The current secular motionestimates, including those generated by the HTDP program, are

based primarily on non-GPS survey data. To maintain and improvethe accuracy of the secular motion estimates, high-accuracy surveys

of the network (or portions of the network) will be required. The

secular motion resurveys and adjustments, as discussed above, will

provide this information. However, network adjustments and newepochs can be delayed by improving the accuracy of the secular

motion estimates through verification surveys. With up-to-date

secular motion information, surveyors can accurately update the

positions of control points, when necessary, either by manual

calculations or through the HTDP program, thus postponing the

need for regional or statewide readjustments. The determination as

to where and when secular motion verification surveys are

necessary shall be a cooperative decision by NGS, the California

Geodetic Control, and California's earth scientists. Secular motionverification surveys will not establish a new published position for

the stations included in the survey. Thus, a new epoch will not be

established. The data from these high-order surveys will be used

only to update the secular motion estimates.

o Continuously Operating GPS Reference Stations: As morecontinuously operating GPS reference stations become operational,

it is anticipated that these stations will provide an increasing

portion of the data necessary for the efforts to determine and

estimate crustal motions (both episodic and secular). Eventually,the use of continuously operating stations will eliminate much of


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the need for "field" crustal motion resurveys (possibly all). See

"Continuously Operating GPS Stations", below.

o Who Accomplishes: Crustal-motion-related surveys shall becooperative projects involving NGS, state/local agencies,

academic/research institutions, and/or private firms. NGS's fieldeffort (resource expenditures) shall include, at a minimum, that

effort required for the Federal Base Network stations. Generally,

NGS shall perform all final data processing and adjustments forcrustal-motion-related surveys. See "Adjustments", below.

7. CSRS "Adopt A Monument" Program: To aid in the maintenanceefforts for the CSRS, the California Geodetic Control Committee willexplore the feasibility of an "Adopt A Monument" program in which

agencies, academic/research institutions, firms, and individuals can

voluntarily assist in maintaining one or more CSRS stations. Theresponsibilities of the sponsor for a CSRS station will be as follows:

o Prepare a "to reach" sketch for the station, in hardcopy andelectronic-media forms conforming to the Committee's standards.(standards to be determined)

o Perform an annual inspection of the station and file a report withthe California NGS State Geodetic Advisor.

o If the station is lost or damaged, assist in the station replacementfield efforts.

o To the extent feasible, assist in crustal-motion-related surveysinvolving the station.

o In recognition of the sponsor's contributions to the CSRS, a notice(standard format to be developed) will be included in the locally-

distributed CSRS data publications (see "Data

Publication/Distribution", above). As the program develops, the

California Geodetic Control Committee will develop other means

to recognize the "Adopt A Monument" participants.


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ADJUSTMENTS:

The general goal for the CSRS is to minimize the number of changes in

published coordinates and epochs.

1.

The California HPGN: Resurveys of HPGN stations will be necessary toreestablished HPGN stations that are lost, damaged, or displaced by

earthquakes, and for periodic readjustments to eliminate accumulated

secular crustal motions. All HPGN resurveys shall be adjusted asdetermined by NGS.

HPGN crustal motion resurveys (secular and episodic) shall be referencedto stable (no crustal motion), high-accuracy, horizontal control on the

North American tectonic plate; i.e., B Order or better National Geodetic

Reference System control. New coordinates, based on the resurveyresults, will be published for all stations in the resurvey, including those

not affected by crustal motion (except the controlling stations on the

North American tectonic plate). The epoch of the new coordinates shallcorrespond to the mean date of the data collection. Resurveys and

adjustments for secular crustal motion will be delayed as long as feasible

to avoid epoch changes. See also "Crustal Motion Resurveys", above.

HPGN resurveys to replace lost or damaged stations, shall be adjusted to

adjacent B Order, Class I HPGN stations as specified for HPGN

densification surveys in the next subsection. The name of the replaced

station will be changed. NGS will perform all final data processing andadjustments for HPGN resurveys.

2. HPGN Densification Surveys: In general, HPGN densification surveysshall be referenced to adjacent B Order, Class I HPGN stations. During

the adjustment process, corrections will be applied to the observations for

the estimated secular crustal motions, as directed by NGS. The epoch of

the densification surveys shall be the epoch of the controlling HPGN

stations.

If secular crustal motions have degraded the B Order, Class I HPGN

control to the extent that a satisfactory adjustment cannot be performedusing the HPGN control, the densification survey shall be adjusted in the

same manner outlined above for HPGN resurveys; i.e., referenced to

geodetic control on the North American tectonic plate. Densification

stations displaced by crustal motions (secular and episodic) shall be

reestablished as part of the HPGN resurvey for the same area (see above),

or such stations shall be reestablished through readjustment methods

involving the HPGN resurvey, data from continuously operating GPS

reference stations, an updated HTDP program, and/or advice from earth

scientists.Resurveys for HPGN densification stations that are lost or damaged shall


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be accomplished and adjusted in the same manner as the original

densification surveys; i.e., referenced to adjacent B Order, Class I HPGN

stations. The name of the replaced station will be changed. NGS will

perform the final data processing and adjustments for HPGN densification

surveys, unless NGS approves the execution (performance) of theseadjustments by others; e.g., the Department of Transportation (Caltrans),

academic institutions, other federal agencies, etc.


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CONTINUOUSLY OPERATING GPS STATIONS:

Continuously operating GPS reference stations (CORSs) are facilities that

collect GPS data on a continuous (24-hour) basis. Often, the data collected is

made available to others through electronic data transfer means. A fee is chargedfor data from some facilities.

The primary benefits of CORSs are: Some CORSs can serve as GPS receivers at known points for geodetic

surveys. Potentially, this could significantly reduce GPS equipment needs

(costs) for GPS surveys.

CORSs provide data which can improve the accuracy of GIS- type GPSsurveys, "freeing up" geodetic-quality field receivers for other surveys.

Similarly, the accuracy and functionality of hand-held GPS receivers canbe improved.

Because CORSs collect data continuously, an instantaneous position canbe computed for the station at scheduled intervals or as needed. Thiscapability provides data to accurately determine secular motions. It also

enables the earth scientists to monitor crustal motions for earthquake

research efforts.

In addition, the instantaneous-positioning-capability permits the positionof a CORS to be reestablished (new coordinates established) immediately

after an earthquake. Resurveys are unnecessary since sufficient data is

available soon after an earthquake to reference the station to other CORSson the North American tectonic plate (and throughout the world).

The California Geodetic Control Committee (CGCC) recognizes the benefits

and expanding use of CORSs. The CGCC has initiated efforts to establish

standards, procedures, and guidelines for this evolving GPS survey

methodology. Preliminary concepts and planned efforts are listed below.

1. The CGCC will encourage owners of CORSs to make their stations,CSRS stations. Efforts to provide the required supplementalinformation (e.g., leveling data) for submittal to NGS might be a

cooperative effort, involving the station owner and others.

2. In general, CORSs included in the CSRS shall ...o Be established in accordance with standards and specifications that

are equal to or better than those outlined in this document for a

CSRS horizontal control station.

o Be included in the NGRS, either as a Federal or Cooperative BaseNetwork station.


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o Have a current published position available from NGS. Preferably,the epoch of the published position shall be the epoch of the nearby

CSRS stations.

o Meet or exceed B Order, Class II accuracy standards andspecifications.

o Be equipped with a geodetic quality receiver, preferably dualfrequencies.

o Have a permanent monument (mark) or other means to verify thatthe position of the GPS receiver antenna has not changed.

o Provide a means by which raw GPS data, in a convenient format, isreadily available to other surveyors.

o When feasible, provide reasonable accommodations which allowssurveyors, who are using the station, to inspect the station for

specific survey-related needs such as for court testimony.

3. Generally, when CORSs are used to determine the position ofunknown points, the unknown positions shall be determined based on

the ....o NGS-published coordinates and epochs for the CORSs ando Raw GPS data from the CORSs.

This procedure will conform to proposed CSRS statutes that areoutlined in this document for the California Coordinate System. See

"Statutes" below.

Certain surveys might use the updated positions of the CORSs

(updated for crustal movements, etc.), to determine the positions ofunknown points as of the epoch date of the survey; e.g., to verify

estimated secular motions.

4. Efforts have been initiated by the CGCC to inventory the CORSs inCalifornia. The Committee plans to publish and maintain a document

that lists these stations with the applicable information for each

station.5. In support of the expected expanding use of CORSs, the CGCC will

compile information and encourage research into the following:

o Guidelines for the establishing CORSs, including receiverstandards, data collection specifications, station accessibility and

monumentation requirements, electronic transmission standards and

formats, and other issues.

o Standards and procedures for performing surveys that use data fromCORSs to establish unknown positions.


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STATUTES:

Another California Geodetic Control Committee document is being prepared, by

another subcommittee, to detail the recommended legislation actions necessary

to establish, maintain, and promote a California Spatial Reference System. To bean effective system, the following key actions will be required.

Add statutes which define the National Geodetic Reference System andthe California Spatial Reference System.

Add a statute which names the horizontal component of the CSRS as theofficial California horizontal spatial reference system.

Clarify and revise existing California Coordinate System (CCS) statutesso that CCS coordinates must be based on direct ties to at least two

permanently-established stations listed below, after December 31, 1999.

(For GPS survey methods, a direct tie means a non-trivial baselinedetermination.)

o National Geodetic Reference System, B Order or better, stations.o California Spatial Reference System stations.o Second Order or better horizontal geodetic control stations

(monuments) shown on a subdivision map, official map, record of

survey, or any map filed with the County Surveyor by a publicofficer, providing the positions (coordinates) of the stations are (i)

established by GPS methods in accordance with the applicable

FGCS or CGCC standards and specifications and are (ii) based on

direct ties to two or more CSRS stations or B Order (or better)NGRS stations.

Notes: Retain last sentence of Section 8813. In Item "c", above, second-order is

consistent with current statute, but inconsistent with today's technology; revise

to first?

Prior to January 1, 2000, the California Geodetic Control Committee and,

hopefully, other professional surveying organizations will promote the use of the

horizontal geodetic control specified above.

Add a CCS provision which requires that documents and electronic filesusing CCS coordinates shall state the epoch (date) that the coordinate data

is valid; i.e., the basis of the coordinate data shown.

Add a CCS provision which requires that documents and electronic filesusing CCS coordinates shall state the order of accuracy, as defined by the

FGCS or CGCC standards and specifications, for all included CCS

control points having an order of accuracy of Second Order or better.

Add a CCS provision which requires that the epoch for a given surveyshall be the latest NGS published epoch of the controlling stations for the


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survey. If the latest published epochs of the controlling stations are not the

same, the epoch of the controlling station having the latest epoch shall be

used.

Appropriate adjustments shall be made to controlling stations havingearlier epochs so that the coordinates of the controlling stations are

consistent.

Add a CCS provision which states that adjustments for crustal motionsshall be made in accordance with NGS-published procedures and values.

CURRENT STATUS (1/94):

1. The California HPGN: The California High-Precision Geodetic Networksurvey established 238, B Order horizontal control stations that aredistributed throughout California (see Appendix A). Field efforts for the

HPGN were completed in 1991, and the station Data Sheets (final

coordinates) were published in August 1992 by NGS.Since the HPGN observations were performed, several earthquakes have

displaced a number of stations. To date, the known areas affected by

earthquakes are in the vicinity of Ferndale, Humbolt County (about eight

stations), Landers, San Bernardino County (44 stations), and Northridge,

Los Angeles county (?? stations). The Ferndale and Landers areas have

been resurveyed. The Landers resurvey data processing and adjustment

are completed and the data is available from NGS. Completion of theFerndale resurvey data processing and adjustment is scheduled to follow

soon. It is anticipated that the resurveys for the Northridge earthquake

will be performed in mid 1994.

2. HPGN Densification Surveys: In addition to the HPGN stations, theproposed CSRS will include about 850, first-order horizontal geodetic

control stations (see Appendix A). A number of surveys have already

been initiated to establish these stations. To date, surveys are underway

for approximately 400 HPGN densification stations. For additional

information, refer to Appendix A.3. Continuously Operating GPS Reference Stations: A recent survey

initiated by the California Geodetic Control Committee identified at least

11 geodetic quality, continuously operating GPS reference stations that

are in operation today throughout California; another 10 stations are

planned in the near future. The Committee will continue to work

cooperatively with the owners of continuously operating stations, and also

will continue to encourage them to incorporate these stations into the

National Geodetic Reference System; and thus, the CSRS. At this time,

the largest network of CORSs is operated by Scripps Institution ofOceanography at the University of California, San Diego. Currently, this


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network, the Permanent GPS Geodetic Array (PGGA), has 10 stations.

Dual-frequency data is collected on a continuous basis at a 30-second

sampling rate. The data is available to PGGA subscribers through a

personal-computer-based bulletin board.

EDUCATION:

Successful implementation and usage of the California Spatial ReferenceSystem will require an effective education program. The California Geodetic

Control Committee is establishing an education subcommittee for this effort.

However, to achieve an official California horizontal spatial reference system(the CSRS) - in "law" by legislation and "in fact" by acceptance and usage - will

require the educational support of California's professional surveying

organizations, State universities, NGS, state/local public agencies, and others.As part of the education program, the CGCC will encourage NGS to develop, in

cooperation with California surveyors, a comprehensive document which

reviews the horizontal geodetic control issues in California and the application(use) of the available information and data. Possible topics should include a

general discussion of California's crustal motions, application of the "Horizontal

Time Dependent Positioning" computer program, definition and use of epoch

data, historical listings of CSRS station shifts (by epoch), and other related

material.


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SUMMARY & STATUS

CALIFORNIA SPATIAL REFERENCE SYSTEM - HORIZONTAL

(HPGN and HPGN Densification)

COUNTYHPGN

Stations

HPGN-D

Stations

Total

Stations

Aera

sq. mi.

Station

Spacing

Alameda 2 10 12 825 8.3

Alpine 0 5 5 727 12.1

Amador 2 5 7 601 9.3

Butte 2 11 13 1,665 11.3

Calaveras 0 7 7 1,036 12.2

Colusa 1 7 8 780 8.4

Contra Costa 3 8 11 780 8.4

Del Norte 4 6 10 1,003 10.0

El Dorado 2 9 11 1,805 12.8

Fresno 7 32 39 5,998 12.4

Glenn 2 6 8 1,319 12.8

Humbolt 4 22 26 3,600 11.8

Imperial 8 18 26 4,597 13.3

Inyo 11 18 29 10,098 18.7

Kern 10 45 55 8,170 12.2

Kings 2 10 12 1,436 10.9

Lake 2 8 10 1,327 11.5

Lassen 7 18 25 4,690 13.7

Los Angeles 7 47 54 4,079 8.7

Madera 2 9 11 2,147 14.0

Marin 3 7 10 588 7.7

Mariposa 1 5 6 1,461 15.6

Mendocino 5 25 30 3,510 10.8

Merced 2 10 12 2,008 12.9

Modoc 6 10 16 4,340 16.5


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Mono 7 12 19 3,103 12.8

Monterey 11 19 30 3,324 10.5

Napa 1 5 6 797 11.5

Nevada 2 7 9 992 10.5

Orange 3 15 8 785 6.6

Placer 4 6 10 1,507 12.3

Plumas 4 8 12 2,618 14.8

Riverside 13 38 51 7,243 11.9

Sacramento 1 8 9 1,015 10.6

San Benito 0 7 7 1,397 14.1

San Bernardino 23 61 84 20,164 15.5

San Diego 9 42 51 4,281 9.2

San Francisco 1 0 1 91 9.5

San Joaquin 3 12 15 1,436 9.8

San Luis Obispo 5 27 32 3,326 10.2

San Mateo 1 6 7 531 8.7

Santa Barbara 7 19 26 2,745 10.3Santa Clara 4 22 26 1,316 7.1

Santa Cruz 1 5 6 440 8.6

Shasta 8 16 24 3,850 12.7

Sierra 0 7 7 959 11.7

Siskiyou 10 18 28 6,318 15.0

Solano 2 5 7 872 11.2

Sonoma 3 17 20 1,598 8.9

Stanislaus 3 9 12 1,521 11.3

Sutter 1 4 5 607 11.0

Tehama 2 10 12 2,976 15.7

Trinity 3 14 17 3,223 13.8

Tulare 5 17 22 4,845 14.8

Tuolumne 2 9 11 2,293 14.4

Ventura 3 18 21 1,864 9.4


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Yolo 1 7 8 1,034 11.4

Yuba 0 4 4 639 12.6

TOTAL 238 832 1,070 158,693 12.2

us california horizontal geodetic net specifications 1994

Documents