> For the complete documentation index, see [llms.txt](https://docs.premium-positioning.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.premium-positioning.com/guides/mountpoint-selection-and-the-gga-heartbeat.md). # Mountpoint selection and the GGA heartbeat A mountpoint is a named correction stream on the caster, and the GGA heartbeat is the message your receiver sends up so the network knows where you are. Choose the right mountpoint and keep the heartbeat flowing, and the network can deliver a correction matched to your position. This page covers both. If the terms are new, [What is NTRIP](/learn/what-is-ntrip.md) introduces the caster, the mountpoint, and the source table first. ### Choosing a mountpoint When your receiver connects to the caster, it can fetch the source table, the caster's published list of available mountpoints. You then pick the one to connect to. For most receivers, COMMON is the right choice. It is the general-purpose network stream and suits the majority of survey, GIS, drone, agriculture, and machine-control receivers. Where more than one mountpoint is available, they usually differ along one of these lines: * Correction type. A network stream interpolates corrections from many surrounding stations and tailors them to your location. A single-base stream carries the observations of one fixed station. * Message set and constellations. Some streams carry a wider set of RTCM messages or more satellite constellations than others. Match this to what your receiver supports. * Region. On a wide network, a stream may be scoped to a coverage area. Which mountpoints you can reach depends on your subscription. If a mountpoint you expect is missing from the list, check that your plan includes it. ### What the GGA heartbeat is The GGA heartbeat is an NMEA message carrying your receiver's approximate position. Your receiver sends it to the caster when it connects, then repeats it at a regular interval for as long as the connection is open. Network corrections are computed for a specific location, so the network has to know where you are before it can generate the right correction. The first GGA tells it where to start; the repeats let it keep the correction matched to you as you move. ### Why it matters on a moving platform On a stationary point, a single GGA would almost do. On a rover, a drone, or an autonomous platform that travels several kilometres, the position the network is correcting for has to follow you. If the heartbeat stops, the network keeps correcting for the last place it heard from, and accuracy drifts the further you go. This is why a dropped heartbeat often shows up as a fix that was fine at the start of a job and degraded across it. ### Enabling and keeping the heartbeat Most receivers send GGA automatically once you select a network mountpoint, and resend it on a set interval you do not normally need to change. The setting is usually labelled send GGA, send position to caster, or send NMEA, depending on the brand. Leave it on for any network mountpoint. A single-base stream does not depend on your position in the same way, so the heartbeat is less critical there, but sending it does no harm and many casters expect it. ### FAQ Which mountpoint should I use? COMMON works for most receivers. Use a different one only if your subscription offers it and you have a specific reason, such as a particular constellation or message set. What is a source table? The caster's list of available mountpoints, which your receiver can fetch once it has the address, port, and your credentials. Why does my receiver send a GGA message? So the network knows your approximate position and can generate a correction matched to it. My fix degrades as I move away from where I started. What is wrong? The GGA heartbeat has most likely stopped, so the network is still correcting for your starting point. Check that position sending is enabled. Next: [Connect a receiver](/set-up-and-connect/connect-a-receiver.md) walks through entering these settings step by step. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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