Hi All,
I intend to develop indigenous DGPS setup using u-blox LEA-6T receiver (single frequency). But for that, we need one base station to act as a reference station (without using internet facilities on the site). I have following questions in mind:
1. Is it possible to use one laptop as a base station i.e. whenever we go out for site experiment, we take this laptop and make it to serve as a base station. Probably for this purpose, we need to do "Precise Point Positioning" for base station everytime we go to the site?
2. Is it good idea to do PPP with single frequency receiver, like u-blox LEA-6T?
3. If yes, then how much time it takes for PPP accurate enough to act as a base station?
4. Is there some other alternative for "mobile" base station i.e. a base station that can be moved to any site?
Thanks for the comments,
Regards,
Replies
Hi Qasim,
I would speculate the following:
You would need a common communication protocol between the 2 receivers like RTCM or CMR. Your base setup would be something like this. A GPS receiver (if your rover is only a L1 receiver, it does not help you have a L1 and L2 base - A L1 base would be sufficient) with a L1 antenna in a fixed position. I'm not sure if you can setup the 6T to export RTCM. I would suspect you can using the uBlox UI. If you can, then you would not need a laptop. You can setup the receiver to stream your RTCM message to a serial radio modem wich will transmit the message to your roving gps. If you can not set the base receiver up to transmit RTCM, then you will have to get an app that takes the uBlox bin format and produces the RTCM string(on your laptop). From here you would transmit the message to you rover via the Radio Modem. This will happen at 1Hz. Timing is important. If the message reaching the rover is aged(2sec+), it will not initialize(fix accurately).
At the rover end you would need a radio modem to recieve the message, a processor to do the mathematical processing and the receiver and antenna itself.
Things to understand of what you are trying to do:
1. Timing is important. If data forwarding takes long, you will only be frustrated.
2. Having a fixed base transmitting any correction will - in essence - allow the calculation of a 3d displacement from the base - it produces a relative displacement solution.
Search the web for openrtk. It is a open RTK library with some handy apps to get a very good understanding of what an accurate GPS system would look like. They also published some papers on receivers they have tested. If memory serves - the 6T took 20 - 30 minutes to initialize and since it is only L1, any signal interruption would cause a loss of RTK fix.
I would suggest start there. They have done a lot of the ground work you require.
There was a discussion around this topic a while ago - Randy mentioned that he can get the correction message to the rover using the telemetry radio. Another component sorted.
Good luck
Antonie