Extracts
https://www.pobonline.com/articles/101399-combining-gnss-and-other-tools-gets-geopositioning-right
Perry Trunick
As global navigation satellite systems (GNSS) have grown in popularity for both commercial and consumer applications, the capabilities of the devices have continued to expand. It’s not surprising to hear companies like Trimble state their newer generation of baseline processing equipment can process baselines over 1,000 km at centimeter level accuracy. Discussing these and other developments, a company spokesman said, “By adding support for some of the additional Galileo constellations, users have a choice on constellations they are using. GPS was necessary because the timing was synchronized on GPS time, now we can process
Galileo only or BeiDou only or GPS only.”
To further enhance or ensure accuracy, the National Geodetic Survey (NGS) manages a network of Continuously Operating Reference Stations (CORS) that provide GNSS data consisting of carrier phase and code range measurements in support of 3D positioning, meteorology, space weather, and geophysical applications throughout the United States, its territories and a few foreign countries, according to the agency.
CORS data can be used to improve position precision, and CORS enhanced post-processed coordinates approach a few centimeters both horizontally and vertically relative to the National Spatial Reference System.
NGS points out that 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. There were roughly 2,000 stations in the CORS network in 2015, contributed by over 200 different organizations.
Indoors isn’t just indoors, suggests Dr. Sanjiv Singh, Near Earth Autonomy. Whether the GNSS-denied environment is underneath a bridge, inside a facility, or in close proximity to large structures (such as a dense urban area), the inertial measurement unit (IMU) or intertial navigation system (INS) will use the initial control point or last known coordinates to continue maintaining the location of the device it is associated with.