Internet ResourcesMost governments will have an agency assigned to maintain a Spatial Reference System to meet economic, social, and environmental needs. Control networks may consist of “hard” monuments that are physical monuments, such as brass caps or chiseled marks on concrete, or “virtual” monuments such as Continuously Operating Reference Stations (CORS). Both will have horizontal or vertical values that reflect the national reference system or vertical datum. Not all nations share the same reference system which can be confusing at times, as there are several kinds of realizations of global geodetic reference systems. Differences among these realizations are caused by slight differences of realized mass centers of the earth, adopted reference ellipsoids and plate motions.
Below are some resources for finding or establishing horizontal or vertical control.
National Geodetic Survey (NGS) - NGS provides the framework for all positioning activities in the Nation. The foundational elements - latitude, longitude, elevation and shoreline information - contribute to informed decision making and impact a wide range of important activities including mapping and charting, flood risk determination, transportation, land use and ecosystem management. NGS' authoritative spatial data, models and tools are vital for the protection and management of natural and manmade resources and support the economic prosperity and environmental health of the Nation. http://www.ngs.noaa.gov/
CORS – NGS manages a network of Continuously Operating Reference Stations (CORS) that provide Global Navigation Satellite System (GNSS) data consisting of carrier phase and code range measurements in support of three dimensional positioning, meteorology, space weather, and geophysical applications throughout the United States, its territories, and a few foreign countries.
Surveyors, GIS users, engineers, scientists, and the public at large that collect GPS data can use CORS data to improve the precision of their positions. CORS enhanced post-processed coordinates approach a few centimeters relative to the National Spatial Reference System, both horizontally and vertically.
The CORS network is a multi-purpose cooperative endeavor involving government, academic, and private organizations. The sites are independently owned and operated. Each agency shares their data with NGS, and NGS in turn analyzes and distributes the data free of charge. As of November 2011, the CORS network contains over 1,800 stations, contributed by over 200 different organizations, and the network continues to expand. http://www.ngs.noaa.gov/CORS/
NGS Data Sheets - Part of the mission of the National Geodetic Survey, is to
provide the public with survey control information, such as Latitude, Longitude, Height and Gravity Data. This is done for publishable stations in the form of DATASHEETS. http://www.ngs.noaa.gov/cgi-bin/datasheet.prl
Online Positioning User Service (OPUS) - OPUS provides simplified access to high-accuracy National Spatial Reference System (NSRS) coordinates. Upload a GPS data file collected with a survey-grade receiver and obtain an NSRS position via email.
OPUS requires minimal user input and uses software which computes coordinates for NGS' Continuously Operating Reference Station (CORS) network. The resulting positions are accurate and consistent with other National Spatial Reference System users.
Your computed NSRS position is sent privately via email, and, if you choose, can also be shared publicly via the NGS website. http://www.ngs.noaa.gov/OPUS/
The NASA Global Differential GPS (GDGPS) System - GDGPS is a complete, highly accurate, and extremely robust real-time GPS monitoring and augmentation system.
Employing a large ground network of real-time reference receivers, innovative network architecture, and award-winning real-time data processing software, the GDGPS System provides decimeter (10 cm) positioning accuracy and sub-nanosecond time transfer accuracy anywhere in the world, on the ground, in the air, and in space, independent of local infrastructure. http://www.gdgps.net/
Automatic Precise Positioning Service (APPS) – APPS offers instant positioning supporting GPS and GLONASS observations. APPS supports file formats in RINEX 2 and RINEX 2.11. Processing Modes include Static and Kinematic. All coordinates are reported in ITRF 2008. http://apps.gdgps.net/apps_file_upload.php
Scripts Orbit and Permanent Array Center (SOPAC) - SOPAC archives high-precision GPS data, particularly for the study of earthquake hazards, tectonic plate motion, crustal deformation, and meteorology. SOPAC calculates and provides precise near real-time and predicted GPS satellite orbits and determines precise polar motion and Earth rotation variations. SOPAC allows users to generate precise coordinates for their input RINEX files using the Scripps Coordinate Update Tool (SCOUT). SOPAC is an International GPS Service (IGS) Global Analysis Center
SCOUT - The Scripps Coordinate Update Tool (SCOUT) can be used to compute mean coordinates of a specific site, by submitting a RINEX file of a particular day. The file may be uncompressed, or in .Z, .gz or .bz compressed format. Both standard observation (o) and hatanaka-compressed (d) files are accepted.
Local ResourcesCity Engineering Offices – City Engineering offices manage public works projects and construction. The City Enginering office will often have elevation benchmark information and horizontal control networks for the City and local area. Beware though, as City benchmarks may become dated or no longer tied to a known reference datum.
Transportation Departments – Transportation offices can be found at City, County, State and Federal levels. Transportation Departments and are a great resource for transportation maps and related horizontal and vertical control networks. Many offices will have an archive of printed and microfiche plans. Transportation engineering and survey departments will also have topographic maps, aerial imagery, control network information and GIS data.
Water and Utility Departments – Water and utility departments manage the resources and assets that are valuable to the area they serve. Water and Utility departments are a good resource for underground utility and waterline maps. Many have GIS departments that keep maps up to date. Water and utility maps are not usually available via the internet due to security issues.
Airports - Airports can be a valuable resource for vertical control benchmarks. Most have been surveyed to determine a precise elevation for landing air traffic. Benchmarks can often be found at runway ends at public and military airports.