This is just for my own personal education. How many Glonass s/v's must be in view for the Glonass to be usefull? I don't understand much of GPS and Glonass integrated systems, this seems to be the step child of GPS surveying. I am also wondering how OTF is facilitated in a GPS+Glonass system for RTK. What are the practical limitations on this type of system?

Thanks
Shawn Billings
SIT Texas

Shawn,

Sorry so long for this reply. Been on the road for the past week or so.

It is my understanding that you need to be observing at least 2 Glonass satellites for the data to be used. At the time of this posting, there are 10 Glonass satellites, 8 of which are currently usable (2 of which have been unusable since early February). With this constellation, in East Texas, using a 10 degree elevation mask, there are 8 hours in the day where fewer than 2 satellites are available. There are 6 hours with 2 satellites, 6 1/2 with 3, 2 hours with 4, and 1 1/2 hours with 5 satellites.

With a well designed GPS+GLONASS receiver, the Glonass satellites are integrated into the solution in such a way that the satellite type is indistinguishable. So for OTF, the Glonass satellites are seen as just more satellites for the solution (as long as you have at least 2).

Hope this helps.

Bill Martin
Ashtech Precision Products