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INTRODUCTION
Positional data collection eff orts performed by personnel and contractors of the Louisiana Department of Transportation and Development
(DOTD) requires a reliable and consistent measurement framework for ensuring accuracy and precision. Global Navigational Satellite
Systems (GNSS) technologies, which include the global positioning system (GPS) maintained by the United States, are used extensively
throughout government and industry. The increased accuracy, reduced cost, and improved effi ciencies of these technologies are rapidly
being adopted for new and existing workfl ows. For this reason, DOTD requires standards and procedures to guide staff and contractors in
the appropriate use of GNSS technology that will ensure application-specifi c data accuracy requirements for mapping-grade devices.
In addition to operational standards, the quality and consistency of GNSS measurements are essential to surveying, engineering design,
and other positional measurement practices. Recent advancements to the national spatial reference system (NSRS), from which horizontal
and vertical positions are measured (i.e., datums), have resulted in signifi cant changes to the way positions are measured when using GNSS
technologies. As a consequence, many professionals, engineers, and scientists have inquired about
the short- and long-term implications of these changes on existing operational practices conducted
within the Department.
Finally, GNSS positional accuracy is essential for numerous DOTD applications. This is particularly
true for the Pavement Management System (PMS) section, which maintains a spatially referenced
inventory of all state maintained roads. This inventory, collected by the Moving Vehicle Rapid
Mapping (MVRM) system, utilizes advanced GNSS and inertial navigation technologies to capture
the horizontal and vertical position of regularly spaced points along state maintained roads and
highways. To assess and ensure the accuracy and precision of this inventory, baseline control
point measurements are needed to evaluate the quality of the data products delivered by DOTD
contractors.
To conduct a three-part study addressing accurate, precise, and consistent positional control for
DOTD.
• Establish standard operation and collection procedures (SOCPs) using GNSS technologies
for mapping-grade applications. SOCPs provide the guidance and standards of practice for
mapping grade devices utilized at the DOTD.
• Summarize the recent enhancements to the nationwide horizontal and vertical spatial
reference frameworks to support consistent and accurate access to the NSRS using modern
GNSS equipment; and to provide recommendations for recording and maintaining GNSS
readings requiring precise, accurate, and consistent vertical control for past, present, and
future projects.
• Conduct and provide multiple baseline surveys on state-maintained roads and highways
in support of quality-control assessments conducted by DOTD personnel. ; and xamine how vehicle speed aff ects horizontal and
vertical accuracy (jointly and separately) from kinematic surveys enhanced by a real-time network.
OBJECTIVE
TECHSUMMARY
September 2015
State Project No. 30001520 / LTRC Project No. 13-6GT
DOTD Standards for GPS Data Collection Accuracy
LTRC CONTACT:
PRINCIPAL INVESTIGATOR:
LTRC Report 539
Joshua Kent, Ph.D.
Center for GeoInformatics
Tyson Rupnow, Ph.D., P.E.
225.767.9124
FUNDING:
SPR: TT-Fed/TT-Reg
Louisiana Transportation
Research Center
4101 Gourrier Ave
Baton Rouge, LA 70808-4443
www.ltrc.lsu.edu
Read online summary or fi nal report:
www.ltrc.lsu.edu/publications.html
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consistent locations that do not require a licensed surveyor.
Furthermore, the SOCPs outlined are not static. Rather, these
operating procedures should be regularly re-evaluated to
evolve as the needs of the department and operator change.
The recent adjustments to the NSRS has improved the
positioning accuracy and precision for all GNSS operators.
These changes, however, require DOTD personnel to become
cognizant of the impact these changes will have on surveyed
positions used in older projects. One-to-one comparisons
are not possible without very specifi c translations and
transformation of the original data.
Finally, the PMS has received and are currently utilizing the
GNSS baseline observations collected at the test sites around
the state. These measurements ensure the quality of the data
products delivered by DOTD contractors.
The department should implement the SOCPs under the
guidance of the GTOC. This should include the creation of
a pool of capable devices, available to staff , to ensure that
mapping grade accuracy is achieved, stored, and available in
the future.
Because terrestrial reference frames are constantly
evolving, it is absolutely imperative that all GNSS-derived
observations include both geometric and geodetic positions.
Corresponding to the best practices typically employed
for surveying, departmental data should include specifi c
references to the horizontal and vertical datums used to
obtain the position. Translating between diff erent realizations
of the same datum [e.g., convert NAD 83 (CORS96) to NAD 83
(NA 2011)] can be accomplished using the same mathematical
computations as those employed for datum transformations.
Tools and resources for performing these recommendations
are both commercially available and within the public domain.
Finally, the horizontal and vertical control surveys conducted
for this project should be used to assess the accuracy and
precision for the MVRM data deliverables. The comparison
of the results on a test site while re-creating the conditions
commonly expected to be experienced in the fi eld will allow
the prediction of the MVRM system performance.
RECOMMENDATIONS
LTRC T
LTRC T
echnical Summary
echnical Summary
539
539
PAGE TWO
Louisiana Transportation Research Center / 4101 Gourrier Ave / Baton Rouge, LA / 70808 / www.ltrc.lsu.edu
Louisiana Transportation Research Center sponsored jointly by the Louisiana Department of Transportation & Development and Louisiana State University
The principle focus of this project dealt with the acquisition,
maintenance, and management of GNSS positioning
data at DOTD. This research is primarily for mapping
grade applications, and is not intended to substitute the
requirements of the more precise DOTD Location and
Surveying Section, but provide guidance for staff and
contractors in the use of this GNSS, generally handheld
equipment, when applicable.
1: Standard Operating and Collection Procedures
Development
An operations and collection procedures document was
developed for mapping-grade GNSS applications utilizing
a hand-held devices. The SOCPs was developed in
coordination through the DOTD GPS Technical Oversight
Committee (GTOC), the project review committee (PRC), and
guidance obtained through LTRC report 11-2P.
2: Horizontal and Vertical Datum Research
The recent changes to the nationwide horizontal and vertical
spatial reference systems were summarized to support
consistent and accurate access to the NSRS. Details also
included recommendations and methods for managing survey
data derived from diff erent realizations of the horizontal and
vertical datums.
3: Control Point Measurements for Pavement Management
System
Horizontal and vertical position measurements were collected
using survey-grade GNSS receives at test sites in each of
the nine DOTD districts. Test sites included mile-long road
segments that were selected by the DOTD and previously
assessed in LTRC Report 09-2GT. Scenario-based kinematic
measurements were also collected at varying speeds using
both mapping and survey grade technologies.
The standards-of-practice for mapping-grade GNSS
technology were examined. The functional accuracy and
precision of the handheld GNSS device were summarized.
Methods, techniques, and recommendations for achieving
optimal positioning were provided in the SOCPs. The SOCPs
developed for this project represent a fi rst of its kind for
operating mapping-grade GNSS devices at DOTD. While it
cannot possibly address every application, the information
and guidance provided within the document will be invaluable
to personnel that need to collect reasonably accurate and
CONCLUSIONS
SCOPE
RESULTS