Primary Control Project Report

This report contains the project description, scope of activities and the report format of the primary control project. Zylstra Baker Surveying, Inc. completed the densification of the Colorado High Accuracy Reference Network in Boulder County Colorado.

The following report details the project description, scope of activities, report format, project discussion, survey reconnaissance and planning, field observations, office calculations, rejected data, least squares adjustment, and comments and recommendations.

Project Description

The purpose of this project was to establish precise horizontal and vertical positions on 51 points in Boulder County and incorporate them into National Geodetic Survey data base through the Bluebooking process.

Scope of Activities

The project consisted of three main parts: 

• Reconnaissance and planning,

• Field observations

• Office calculations

In all three aspects the following factors were taken into consideration and met:

• The establishment of a network of monumented points.
• Precise measurements in accordance with the Federal Geodetic Control Committee and the Colorado Department of Transportation.
• Accuracy specifications of a First Order horizontal, class II vertical survey or 1:100,000 within a 95% confidence level.
• Adjust the network to tie in with existing monumentation.
• Submittal to National Geodetic Survey for inclusion into the database.

Report Format

This report includes four main sections:

• Project discussion
• Station information
• Session observation information
• Attachments and software output

Project Discussion

The Project discussion contains four main parts:

• Survey Reconnaissance and Planning
• Field Observations
• Office Calculations
• Comments and Recommendations

Survey Reconnaissance & Planning

Reconnaissance

Reconnaissance of the project points was performed by Richard Cohen, Colorado Department of Transportation State Geodetic Advisor and John Mosher, Boulder County Maintenance Supervisor. The project is located in Boulder County, Colorado and is approximately 24 miles wide by 33 miles long. At the time of reconnaissance, site photographs were taken which included pictures taken to the north, east, south, west and a close up of the monument. In addition to the photographs, site obstruction, recovery descriptions and additional reference points were measured where necessary and applicable.

Netware Design

The survey consisted of establishing GPS derived horizontal and vertical positions on a total of (51) stations. The network had to meet the standards of a First Order survey as published by the Federal Geodetic Control Committee. The survey performed exceeds the standards with double occupation at all points and triple occupation at (14) of the (51) or 27% triple occupation. In addition to the occupation standards, the requirement for redundant baseline observation was also exceeded with (8) of (51) or 8% of the baselines with double or triple observation.

The network was designed by Lawrence de Vries of Zylstra Baker Surveying, Inc., Geodetic and Control Survey Coordinator. The network was approved by Richard Cohen, Colorado Department of Transportation State Geodetic Advisor.

Mission Planning

The mission planning was performed incorporating the obstruction diagrams, taken during the time of reconnaissance, to ensure proper satellite geometry and favorable times to avoid any possible obstructions. Mission planning was performed by Lawrence de Vries of Zylstra Baker Surveying, Inc.,Zylstra Baker Surveying, Inc. will be referred to later in this report as ZBS.

Monumentation

The project incorporated existing NGS published stations from a previous GPS network tied to an old triangulation network. New positions were to be established at these stations referenced to the Colorado High Accuracy Reference Network. A total of (16) of the old GPS network stations were re-established and are as follows:

• Magnolia
• Nederland
• Peak
• Pony
• T 320 Reset
• TT 23 J
• Ward
• Caribou Hill
• Erie
• Austin
• Buff
• Bunce
• Gunbarrel
• Happy Jack
• Howrich
• Legion

The following points are also published but not tied to the previous GPS network:

• Q 410 (First Order vertical control)
• C 411 (First Order vertical control)
• 8443 DENV (First Order horizontal control)
• Lyons (B Order horizontal control)
• Overlook (B Order horizontal control)
• V 164 (First Order horizontal and Second Order Vertical control)
• Wanaka (First Order horizontal control)
• Jeffco Reset (First Order horizontal and vertical control)
• B 322 Reset (First Order vertical control)
• Energy (Conventional First Order, not used as control)
• M 361 (B Order horizontal control)
• Barbara (Conventional First Order, not used as control)

In addition to the above points a total of (23) new marks were set in accordance to National Geodetic Survey and Colorado Department of Transportation Guidelines; please see the section entitled Hard Copy DFILE for various setting types of the new stations established.

Field Observations

Observations

The field observations were a joint venture between the Colorado Department of Transportation (to be referred to later in this report as CDOT) Region IV, ZBS, Bureau of Land Management and Boulder County. All field observations were taken in accordance with CDOT Static Global Positioning System Survey Procedures; please reference attachments: "CDOT GPS AND GEODETIC SURVEYING" and "CDOT Field Setup of Equipment for Static Surveys".

Personnel Involved

Observations were taken by the following personnel:

• Lawrence de Vries ZBS
• Randy Fellows ZBS
• William Gabonay Bureau of Land Management
• Robert Saiz Bureau of Land Management
• John Mosher Boulder County
• Arthur LaCombe CDOT Region IV
• Charles Northrup CDOT Region IV
• Lee Groves CDOT Region IV
• Lee Ireton CDOT Region IV
• Edward Warwick CDOT Region IV
• John Obrochta CDOT Region IV

Weather Influences

During the project there were instances of rain and snow which inhibited the taking of the station rubbings. During these times the cap was verified that it was the correct station. All stations affected by the weather conditions had station rubbings taken at another time during the project.

Equipment Used

The equipment used was a combination of CDOT and ZBS's. ZBS provided one Trimble Navigation, Ltd. 4000 Ssi receiver and one Trimble Navigation, Ltd. 4000 SSE receiver. CDOT provided two Trimble Navigation Ltd. 4000 Ssi receivers, two Trimble Navigation, Ltd. 4000 SST receivers and two Trimble Navigation, Ltd 4800 receivers. All receivers are dual-frequency and are listed as follows:

CDOT Receivers

ZBS Receivers

All receivers were configured to log data at the 15-second epoch interval. All elevation masks in the receivers were set to 15 degrees while observing. The minimum number of satellites observed was four at any given time.

In addition to the equipment listed above accessories to such were used and are as follows:

• Tripods
• Barometers
• Belfort weather stations (temperature and relative humidity)
• Precise levels (to eliminate tribrach centering error)
• Power and antenna cables (for receivers)
• Tribrachs
• Sand bags (for tripod feet)
• Wood stakes (for tripod feet)
• Sealed lead acid batteries (for receivers)

Zero Baseline Calibration

Adhering to CDOT standards, it was necessary to perform a zero baseline calibration on all of the receivers. A zero baseline calibration ensures that the receivers are collecting data correctly and that the vector processing software is arriving at the proper solutions. The basic methodology of a zero baseline consists of multiple receivers collecting data through a single antenna. CDOT and ZBS performed independent zero baseline tests on their respective receivers; please see attachments: CDOT Zero Baseline and ZBS Zero Baseline for test results.

Data Download

The data was downloaded at the end of each observation day by Lawrence de Vries of ZBS using a Compaq Presario® laptop with an AMD-K6 (tm) 266 MHZ processor, 96 megabytes of memory, 4.0 gigabyte hard drive and Windows® 98. The data were processed using Trimble Navigation Ltd.'s GPSurvey version 2.30a. to check for any possible problems with the data.

Problems Encountered in the Field

Problems were experienced with the downloading of the SST receivers using GPLoad, the Trimble Navigation, Ltd. utility used for downloading of Trimble receivers. The software and the receivers would not communicate. It is my belief that the speed of the newer computers in comparison to the relative age of the SST receivers makes the two incompatible due to differing processing speeds. With this in mind, the older GPSurvey software was looked at to see what utility was used in the downloading of previous data from the older receivers. A Trimble utility called Win4000 was used. This utility is also available in the in current versions up to GPSurvey 2.30a. It is a sub program not accessible in the GPSurvey program, it is available in the GPSurvey Bin directory were various other utilities are located. The use of this program eliminated all previous problems encountered.

Power failures occurred with one of the SST receivers on day 207 session 2 and day 209 session 1. Re-observations were scheduled at the end of the project to obtain the needed baseline vectors.

Office Calculations

Point Descriptions

The project point descriptions were prepared by Richard S. Cohen, CDOT State Geodetic Advisor using the NGS program DDPROC.

Vector Processing

The GPS vector data were processed with Trimble Navigation Ltd.'s GPSurvey version 2.30a and Wave baseline processor version 2.30a. The data were processed on a Touch computer with an AMD-K6 (tm) 133 MHZ processor, 64.0 megabytes of memory, 10.0 gigabyte hard drive and Windows® 98.

Personnel Involved

The data were processed by Lawrence de Vries of Zylstra Baker Surveying, Inc.

Precise Ephemerides

Precise ephemerides were used to obtain greater accuracy in the GPS vector processing. Precise ephemerides were downloaded from the NGS Internet web site located at www.ngs.noaa.gov.

Solutions Obtained

All of the solutions obtained from the processing of the GPS vectors were ionospheric free fixed. Please see the attachment Vector Solution Summary for summaries of the baseline solutions.

Problems Encountered during Vector Processing

No problems were encountered during the vector processing.

Rejected Data

The GPS data collected by William Gabonay for day 207 session 2 and day 209 session 1 was rejected due to the aforementioned power failures.

Least Squares Adjustment

Preliminary Adjustment

A preliminary adjustment was performed using Trimble Navigation Ltd.'s TRIMNET Plus version 92.11c. A minimum and full constraint adjustment was performed to detect any possible network problems.

Software Used

The software used to least squares adjust the GPS vector data was NGS's ADJUST version 4.12 and it's utility components downloaded from the NGS internet web site on May 3, 1999.

Personnel Involved

The network was adjusted by Lawrence de Vries of ZBS.

Geoid Model

The Geoid model used was Geoid 96 as published by NGS.

Minimum Constraint Adjustment

The horizontal minimum constraint adjustment was performed fixing the position of station OVERLOOK. After the first minimum constraint adjustment the variance factor was scaled by a value of 4.90 as determined by the standard deviation of unit weight from the first horizontal minimum constraint. The vertical minimum constraint was performed fixing station V 164. There were no apparent problems after the minimum constraint adjustments.

Full Constraint Adjustment

The process used was to perform two separate full constraint adjustments, one horizontal and one vertical, and then combine the results. The scale factor as determined in the minimum constraint adjustment was applied to both adjustments. The latitude, longitude and ellipsoid heights of the following points were constrained in the horizontal adjustment:

• 8443 DENV
• COPELAND
• LYONS
• OVERLOOK
• V 164
• JEFFCO RESET
• M 361

The latitude, longitude and orthometric elevation of V 164 were held fixed in the vertical adjustment in addition to the orthometric elevations of the following points:

• Q 410
• C 411>
• 8443 DENV
• T 320 RESET
• TT 23 J
• JEFFCO RESET
• W 410
• B 322 RESET
• M 361

Problems Encountered during Adjustment

No substantial problems were encountered during the least squares adjustment other than slight file format problems between GPSurvey and the ADJUST program file formats. To resolve this problem certain data had to be manually entered into the files.

In addition to the GPSurvey program file format problems Zylstra Baker Surveying, Inc. had not been updated in the Agency.dat file, ZYLSTR was entered into the Agency.dat file. ZYLSTR was assigned to Zylstra Baker Surveying, Inc. in National Geodetic Survey project GPS 1335, the Morgan County, Colorado GPS Project computed in 1998.

Comments and Recommendations

This project was particularly interesting because it re-established positions obtained from an old GPS network tied to the Colorado triangulation network to positions referenced to the Colorado High Accuracy Network. The shifts observed between the previous positions and the new positions were seen at the decimeter level.

Overall the project went relatively well and there are no recommendations for future GPS projects.

 

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