GGA Interval in NTIP

How often does this need to be updating?

Don’t think it is needed at all except for a VRS correction signal. Or if you want to see the vehicle location at the base site.

Thats right. Only necessary for VRS RTK networks. You can also set a fixed location in ntrip if you near a border and the VRS doesn’t work outside your country.

I’m using a state RTK system for corrections. So I would set the GGA intervals to to 0?


That does not say much. Actually my guess is that “a state RTK system” is a VRS service. In any case it would not harm having the GGA interval set (to any decent figure). If you try with 0 and it doesn’t work, then you know the caster expects your location info.

The State of Iowa, USA has what they named Iowa Real Time Network ( I’m subscribed to it instead of my own base. I have 2 sites close to me ( 7 and 15 miles).

Maybe I should have worded my question differently.

What is a reasonable amount of time between requests for the correction information? The default of 20 seconds seems to me to be over kill. Even the max of 600 seconds seems to me to be often enough. Since this is my first experience with GNSS and RTK I readily admit to my ignorance. I’d appreciate any education that you’d care to share.

Seems you have misunderstood the AOG setting for the GGA interval. It is not a request for the correction data delivery frequency but the frequency the rover sends its position information back to the NTRIP caster.

The caster usually sends most important RTCM messages once per second irrespectively of this GGA parameter. The caster only needs the rover position information if it calculates a virtual base station close to the rover or if they automatically select the closest base amongst many. I could not open the link for iowadot to check if they use a virtual station but since you mention two sites near you, I’d keep GGA feedback active (at any rate you prefer).

I don’t know if they would switch the correction source when you move from the coverage of one base to another (another one becoming the closest base). You might want to avoid that (if not driving too far from the first base) but on a well built network you would not need to avoid the change.

EDIT: managed to access the iowadot info, they use Leica Spidernet SW, a complicated system and definitely needs GGA from their rovers. The default AOG setting should anyway be fine.

Correct, the GGA sent back is only a requirement if the caster needs it. The best thing to do is see if it only needs the first one (always sent a couple times) and can be set to 0. Not all casters need the rover position, so for sure, sending it every 20 seconds when not even required is a huge waste of data.

Once every 600 seconds, that is not much data - but then you may as well set to 0

Thank you folks. I appreciate the info. Do you have any good reference material I could read?