Global Positioning Systems


Great Smoky Mountains National Park does not provide any characterization on the accuracy or precision on commercial, consumer-grade hand-held GPS equipment or GPS-enabled mobile devices such as smart phones. In general, visitors can comfortably assume that most devices are capable of 5 meters of hoizontal accuracy. The USDA Forest Service maintains a summary of tested horizontal accuracies for different receiver models. It is very important to know that while the GPS signal your device is receiving may be within 5 meters, the base map on your device is probably not. The park has direct and negative experience with most commercial base maps which generally depict incorrect road names, roads that don't exist, trails that go in the wrong direction, etc.

Vehicle Navigation Systems and GPS units may provide inaccurate information in the mountains—sending drivers the wrong way on one-way roads or leading them to dead ends in remote areas. Free park road maps are available in park visitor centers. Mobile device users can download a free application and detailed 2017 topographic maps for accurate navigation in areas without cellular service.

Visitors can check the accuracy of their device or smart phone by recovering a National Geodetic Survey Benchmark, with the Newfound Gap Parking Lot benchmark FB4079 being very easy to find, accessible, and a very unrestricted view of the sattelite constellation.

Park research partners collecting permitted data are encouraged to contact park staff to coordinate the park standard GPS data collection format. This allows the park to easily ingest your data, as well as make your research more easily reproduced. The most common scenario is needing to revisit established plot locations in order to measure the amount of population change in a particular species.

Many differential correction services provide coverage within the park boundary. For those front country areas with cellular reception, the states of North Carolina and Tennessee provide a real time correction service for a fee. The park is unable to provide access to park-owned correction accounts, researchers must provide their own equipment and subscription.

Satellite-based correction services generally work in most areas of the park, however dense canopy and deep valleys have been found to greate reduce the quality of the service, and in most areas of the park, convergence time is in excess of 30 minutes.

Contractors working for the park are encouraged to use Real-time kinematic (RTK) GPS when projects require surveying. In general, most previously established benchmarks are no longer recoverable and a local control point will need to be established. Installation of a control point other than a nail (rebar, concrete) will require concurrence from the parks NEPA specialist.

Depending on the scope and size of the project, the park may be able to establish an OPUS control point and optionally a shared solution.

Many differential correction services provide coverage within the park boundary. For those front country areas with cellular reception, the states of North Carolina and Tennessee provide a real time correction service for a fee. The park is unable to provide access to park-owned correction accounts, contractors must provide their own equipment and subscription.

NTRIP For Public Use

The park does provide access to a free Networked Transport of RTCM via Internet Protocol (NTRIP ) correction service for public use. The base station is located in a non-publicly accessible location in the Gatlinburg area therefore no shared solution is available. Surveyors working in the Gatlinburg area are able to utilize this public correction signal via the internet. Technical support, however, is not available and no warrantees or guarantees are made regarding the availability of the service, its quality, or accuracy. In addition, the park is unable to assist with receiver configuration to access this service. Public users experiencing difficulty with this service should contact their GPS vendor. Contractors and researchers esperiencing difficulty in accessing the correction service should contact their park project representative.


RINEX files from the base station, a Trimble NETR9, are rolled up on a monthly basis.. Contractors and researchers needing access to the RINEX files on a time-dependement basis should contact their park representative. The logging rate is set to
a 1 second measurement interval and a 10 minute position interval. The park is unable to change the logging rate under any circumstance.
The address of the NPS NTRIP Caster is The user name is GRSM and the password is GRSM, both case sensitive. The mountpoint is GRSM_RTCM3x on port 2101. If an issue is reported to the park about the status or functionality of the NPS NTRIP service, all the park is able to do (for all user categories) is confirm the service is working. Users of the NPS NTRIP service that are encountering techincal difficulties that are not related to a service outage will need to contact their GPS vendor techincal suppport.

The OPUS position of the antenna is as follows:

USER: DATE: January 16, 2020
RINEX FILE: grsm3360.19o TIME: 20:23:26 UTC

SOFTWARE: page5 1801.18 160321 START: 2019/12/02 00:00:00
EPHEMERIS: igs20821.eph [precise] STOP: 2019/12/02 23:59:00
NAV FILE: brdc3360.19n OBS USED: 50241 / 52614 : 95%
ANT NAME: TRM115000.10 NONE # FIXED AMB: 187 / 214 : 87%

REF FRAME: NAD_83(2011)(EPOCH:2010.0000) ITRF2014 (EPOCH:2019.9192)

X: 584041.475(m) 0.005(m) 584040.599(m) 0.005(m)
Y: -5153337.049(m) 0.010(m) -5153335.592(m) 0.010(m)
Z: 3700752.098(m) 0.002(m) 3700751.983(m) 0.002(m)

LAT: 35 41 32.13589 0.007(m) 35 41 32.16214 0.007(m)
E LON: 276 27 57.22157 0.006(m) 276 27 57.19349 0.006(m)
W LON: 83 32 2.77843 0.006(m) 83 32 2.80651 0.006(m)
EL HGT: 408.959(m) 0.007(m) 407.636(m) 0.007(m)
ORTHO HGT: 438.382(m) 0.044(m) [NAVD88 (Computed using GEOID18)]

UTM (Zone 17) SPC (4100 TN)
Northing (Y) [meters] 3952776.065 153583.053
Easting (X) [meters] 270699.023 823160.315
Convergence [degrees] -1.47912222 1.44363333
Point Scale 1.00024796 0.99995145
Combined Factor 1.00018376 0.99988727


DL2762 NCBC BRYSON CITY CORS ARP N352221.562 W0833023.371 35551.5
DL2078 TN17 TDOT DISTRICT 17 CORS ARP N354848.158 W0840017.535 44650.9
DJ9536 TN13 TDOT DISTRICT 13 CORS ARP N355637.031 W0831226.416 40620.9

FB1800 TTS 1 N354100015. W0833200005. 507.7

This position and the above vector components were computed without any
knowledge by the National Geodetic Survey regarding the equipment or
field operating procedures used.

Last updated: March 6, 2020

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107 Park Headquarters Road
Gatlinburg, TN 37738


(865) 436-1200

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