RTK GPS with 4G NTRIP: Centimeter Accuracy for Developers

RTK (Real-Time Kinematic) achieves centimeter-level accuracy by utilizing both code phase and carrier phase corrections. While code phase measurements provide standard GNSS accuracy, carrier phase measurements are typically orders of magnitude more precise. This fundamental difference explains how RTK can achieve the dramatic improvement from sub-meter to centimeter-level accuracy compared to standard GNSS solutions that rely only on code phase corrections.

Code phase measurements are typically two orders of magnitude less precise than carrier phase measurements. This fundamental difference explains why DGNSS (using only code phase correction) is limited to sub-meter accuracy while RTK (combining code and carrier phase correction) achieves centimeter-level precision. The carrier phase measurement's superior precision enables the dramatic improvement in positioning accuracy when both correction types are applied together in RTK systems.

RTK achieves centimeter-level precision using carrier phase measurements rather than code-based ranging. The carrier wave's phase allows millimeter-to-centimeter distance measurement, but introduces integer ambiguity—the unknown whole number of cycles between satellite and receiver—which requires resolution through algorithms like double differencing and Kalman filtering. RTK uses a stationary base station and mobile rover, with the base generating correction signals transmitted via RTCM SC104 protocol. Operating within 10-20 km range, RTK provides real-time results with accuracy of ±2 cm compared to DGPS's ±1 m.

GNSS receivers use two primary measurement types. Pseudo range measures distance based on signal transmission time but suffers from significant errors including the Sagnak effect caused by Earth's rotation. Carrier phase measurement uses the sinusoidal wave properties of satellite signals to determine position with much higher precision. By resolving the number of signal cycles transmitted and received, carrier phase can achieve millimeter-level accuracy (about 2mm for L1 carrier), compared to meters for pseudo range measurements.

RTK uses both the PRN (pseudo-random number) and carrier phase measurements. The carrier phase is the phase of the radio signal's carrier wave. By measuring the phase difference between the expected and received signal, the receiver can compute the distance to the satellite with much greater precision than using the PRN alone.

This section covers NTRIP (Network Transport of RTCM via Internet Protocol) as an alternative to radio transmission. NTRIP transmits corrections via the internet, overcoming radio signal limitations by using cellular or internet connections. The system consists of three components: (1) Server - converts RTCM corrections to IP data format, (2) Caster - centralizes and redistributes data from multiple servers, (3) Client - receives corrections and transmits them to the rover. This architecture allows multiple users to access correction data simultaneously. The presenter explains that this is particularly useful in urban or mountainous areas where radio signals cannot reach, and that municipal stations like San José's provide free access to this infrastructure.

Continuous monitoring stations are fundamental for determining real-time coordinates with multiple cartographic purposes, maintaining updated national geodetic reference frameworks by incorporating time as a fourth coordinate. The Ecuadorian network of active stations meets rigorous parameters to qualify as part of the SIRGAS regional geocentric system. In 2013, data was released for public institutions and academia, and in 2020, the network became the most dense and homogeneous at the Pan-American level. Stations receive signals from multiple constellations (Galileo, GPS, GLONASS, Beidou), ensuring greater redundancy and precision with approximately forty satellites engaged. The REGME IP service, developed by the Institute Geográfico Militar and Escuela Superior Politécnica de Chimborazo, provides free real-time positioning through NTRIP protocol. The network architecture consists of three components: the spatial segment (GNSS satellites and ground antennas), the Encrip source (generating RTCM correction streams), and the NTRIP caster (distributing corrections to users). The service uses two casters for redundancy: primary at IGM in Quito and backup at ESPOCH in Riobamba. NTRIP (Networked Transport of RTCM via Internet Protocol) is a protocol developed by the German Federal Agency for Cartography and Geodesy (BKG) responsible for packaging GNSS station information into RTCM format for internet transmission. The protocol consists of four components: NTRIP source, NTRIP caster, and NTRIP client (users). RTCM is a standard format for transmitting differential GNSS correction messages, enabling interoperability between different brands and technologies. The service uses RTCM versions 2.3 and 3.0, with version 3.0 being lighter and allowing centimeter-level precision. The REGME IP service provides automatic alignment to the SIRGAS Ecuador reference frame (TDF 2008 epoch 2016.4), ensuring all coordinates are consistent with the official national geodetic reference. For optimal results, the distance between monitoring station and rover must be considered: 50 km maximum for dual-frequency L1/L2 equipment, 25 km for single-frequency L1 equipment. Mandatory conditions include internet connectivity (2G, 3G, 4G, Wi-Fi), client compatibility with NTRIP protocol and RTCM 2.3/3.0 formats, and consideration of environmental conditions to avoid signal multipath. Precision depends on rover equipment characteristics, with estimated horizontal and vertical precision in centimeters, with field experience showing decimeter-level accuracy in some cases. To access REGME IP, users must register through the IGM Geo Portal by entering information in specific fields and reading usage license terms. After registration, users receive credentials via email that are non-transferable. The Geo Portal provides a geographic visualizer showing available stations and links to mobile operator coverage maps.

RTK (Real-Time Kinematic) GPS technology enhances standard GPS accuracy from meters to subcentimeter precision by using a fixed base station that monitors GPS signal variances and transmits corrections to mobile receivers. NTRIP (Networked Transport of RTCM via Internet Protocol) casters enable distribution of these corrections over internet connections, extending operational range beyond line-of-sight radio limitations to approximately 20 kilometers. This technology serves professionals including surveyors, architects, archaeologists, and drone operators who require precise spatial measurements. Emlid's Reach series offers accessible NTRIP caster solutions with free tiers supporting multiple mount points and simultaneous connections.

NTRIP (Networked Transport of RTCM via Internet Protocol) enables centimeter-level GNSS precision without physical base stations. Unlike single-base systems limited to 10-20km, NTRIP networks provide multiple reference stations across coverage areas, transmitting all GNSS constellations (GPS, GLONASS, Galileo, Beidou) and all frequency bands (L1, L2, L5, L6). Reference stations calculate atmospheric and satellite errors, transmitting data to central servers that calculate position-specific corrections. Applications include drone mapping (DJI Enterprise series), precision agriculture, topography, and autonomous vehicles. The system uses RTCM protocol with PPP RTK technology achieving 3cm horizontal precision. Not all equipment supports NTRIP—only professional equipment with RTK-capable receivers can utilize it. Subscription plans range from 10-hour test (~$13.95) to annual (~$499.95), providing cost-effective access compared to physical base stations ($25,000-$30,000).

This segment explains the NTRIP (Network Transport of RTCM via Internet Protocol) for real-time GNSS corrections. Unlike traditional radio-based differential corrections, NTRIP uses internet packets to transmit correction data, eliminating distance limitations. The segment describes the caster system architecture consisting of reference stations, a central server, and user receivers. The presenter explains how correction data flows from reference stations to the caster server via internet connections, then to users. The segment covers implementation requirements including continuous internet connectivity and discusses the evolution from 2G to 4G networks improving real-time performance.

After connecting to the dash cam's Wi-Fi, activate the SIM card by: (1) Tapping the SIM card button in the app, (2) Entering the cell phone provider's APN (Access Point Name) settings, (3) For T-Mobile in the US, select the T-Mobile APN option, (4) Skip username and password fields, (5) Save to activate. This enables the dash cam to connect to the internet via the SIM card.

This segment details the complete SIM card activation process and mobile data configuration. The presenter walks through inserting the SIM, receiving activation messages, and completing the activation via the Diri app. A critical technical step involves configuring the APN (Access Point Name) settings, where the presenter demonstrates adding a new APN with the specific settings for Diri Telecomunicaciones (internet.ddiri.com). Without proper APN configuration, mobile data connectivity will not function even after successful SIM activation.

This tutorial demonstrates how to activate and register a WOM SIM card, configure APN settings for data connectivity, and perform number portability to switch carriers while keeping the same phone number. The process involves using the carrier's website to complete registration with personal identification details, configuring APN settings through the device's network settings menu (typically accessed via Settings > SIM & Mobile Networks > Access Point Names), and entering the correct APN credentials (such as 'internet.uom') to establish data connectivity.

This segment details the critical configuration steps for connecting the module to a monitoring center. Essential topics include: obtaining and entering the monitoring center's IP address and port (default: 8766); configuring TCP/IP communication protocol; setting up SIM card APN settings (e.g., internet.claro.com.co for Colombian Claro); and understanding the importance of accurate configuration for reliable alarm reporting. The module requires proper SIM card installation with correct APN settings to enable cellular data communication for alarm transmission.

After SIM installation, configure APN (Access Point Name) settings for internet connectivity. Navigate to Settings > Wireless and Network > Access Point Names. Use existing carrier settings or create new ones by tapping 'New APN.' Configure five fields: Name, APN, Username, Password, and Authentication Type. All characters must be in half-width format. Save settings to apply changes. Most connectivity issues stem from typing errors in these settings.