Get RTK corrections over NTRIP

A receiver needs corrections from a base station to get an RTK fixed solution. OpenSurvey3D has a built-in NTRIP client. It connects to a caster over the phone's internet connection and forwards the corrections to your receiver.

Before you start

• Connect your receiver first. Corrections have nowhere to go without it. See Connect a Bluetooth receiver or Connect a Wi-Fi receiver.
• Have your caster details ready: host, port, mountpoint, and a username and password if the caster needs them.
• The phone needs an internet connection.

Connect corrections

1. Hold the accuracy pill to open Precision.
2. Under NTRIP corrections, fill in:
   • Caster host: for example rtk2go.com, which is the starting value.
   • Port: usually 2101, the starting value.
   • Mountpoint: type it, or tap Browse mountpoints… to pick from the caster's list.
   • Username (optional) and Password (optional): tap the eye to show or hide the password.
3. Tap Connect corrections.
4. The section shows Corrections with the amount received, and Data age in seconds. In the pill, the correction age appears and the fix should move from single to float to RTK FIXED.

Connect corrections is greyed out until you've entered a mountpoint and the receiver is connected on a link that can carry corrections.

To stop, tap Disconnect corrections.

Browse mountpoints

Browse mountpoints… downloads the caster's sourcetable, its list of streams, using the host, port and login you've entered.

• The list is sorted by distance from your position, closest first: "Closer bases give better RTK baselines." Without a position it's alphabetical.
• Search by name, city, network, country, format or constellation.
• Each row shows the mountpoint name, a lock if it needs a login, a $ if the caster marks it as fee-based, the constellations, the format and network, and the distance.
• Tap a row to use it. A check mark shows the one currently selected.
• Tap browse on map at the top to see the mountpoints on a map (Map or Satellite). Purple markers are available and green is your current one. Tap a marker for details: Station, Format, Messages, Constellations, Network, Country, Distance, Bitrate, Sends GGA and Login required. Then tap Use this mountpoint. Mountpoints without coordinates are listed but can't be mapped.
• Use the refresh button to reload the list. If it fails, you see Couldn't load mountpoints with the reason and Retry.

Saved casters

Tap Saved casters… to keep caster settings for one-tap reuse.

• Tap an entry to load its host, port, mountpoint, username and password into the connection fields. The active one has a green check mark.
• Tap + to save the settings currently in the fields as a new entry. Give it a Name. The Add caster sheet needs a name and a host before Save works.
• Swipe left on an entry for Edit and Delete.

The list starts with three entries:

If you delete one of these, it stays deleted.

KYCORS

KYCORS is free for Kentucky users. Register at kycors.ky.gov and KYTC emails you the caster address, port and your login. Swipe the KYCORS entry, tap Edit, and fill in Host, Port, Username and Password. Its mountpoints are VRS (RTCM3), and the app sends your position to the caster automatically.

Your position is sent to the caster

Network (VRS) casters need to know roughly where you are to build corrections for your location. When corrections connect, and every 10 seconds after, the app sends your position to the caster as an NMEA GGA sentence. It uses the receiver's position while the receiver is delivering fixes, and the phone's position otherwise. The mountpoint details show Sends GGA: Yes (VRS) for streams that expect it.

Passwords and privacy

• The password for the connection fields, and each saved caster's password, are stored in the iOS Keychain, never in plain text.
• On each observation the app records where corrections came from as host:port/MOUNTPOINT. Your username and password are never recorded. The source is only recorded while corrections are actually reaching the receiver.

Connection states and errors

If a caster accepts the connection but sends nothing within 15 seconds, which usually means the wrong port, the app drops it and retries.

The fix never gets better than float

• Check the pill's correction age. no corrections or a large, red-orange age means corrections aren't reaching the receiver.
• Check the RTK corrections graph in Receiver status. If bytes are arriving from the caster but the receiver isn't using them, the problem is between the app and the receiver.
• Check Corrections link in Receiver status. Not available means the Bluetooth link can't carry corrections. Power-cycle the receiver and reconnect.
• Check the base distance. Long baselines take longer to fix and may not fix at all. Pick a closer mountpoint.
• Check the format. The receiver must support the stream's format (usually RTCM 3) and constellations.
• Bad Elf receivers: forwarding corrections from this app is for Extreme models and hasn't been confirmed on hardware. If it stays at float, run NTRIP from the Bad Elf Flex app instead.
• Give it time and sky. Under trees or near buildings, a fix can take a long time or never come.

Related

• Read the accuracy pill
• Connect a Bluetooth receiver
• Connect a Wi-Fi receiver
• Coordinate systems
• Free NTRIP casters and CORS networks
• NAD83 vs ITRF: datums and epochs