I've heard the 4-6 hrs time separation is overstated. A study out of the UK showed that 40 minutes was enough change in the constellation that the benefit from more time separation was negligible.
> Besides Dead batteries, and mechanical failures,
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> This thread pertains to accuracy.
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> Kids move your base nail a few feet. OR somebody else set a BASE nail on the SAME hill, and you are not finding YOUR nail. This is for multiple days, on the same base site, maybe even several months, or years apart. (check to something)
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> You are staking a corner. Mild woods. You get within 10 ft of the corner, with a float, and set it up, and wait for a fix. It says xxx brg and dist. You use your compass, and box tape to move the 6 feet to the corner, and then move your gps system to the corner, and it says FIXED, move 0.10' and you set your corner, and you ASSUME you are good. BUT you did not loose lock between the 2 observations. They were BOTH wrong by the same amount, and the same direction. So, you carried your bad initialization between the shots, and set your corner wrong by the amount of error, at the 1st fixed observation.
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> You set your base station up near a metal roof barn. Multi path is coming from that roof. Your corrections are gonna bounce around all day. Search carefully so that you do NOT set your base in a multipath environment.
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> If you need to observe with your rover, in a bad environment, for multipath, then walk AWAY from the bad environment, to CLEAR sky, re-initilize, and walk back to your needed point, in the bad environment, CARRYING your fix. This usually gets it right, but the LOCAL accuracy is poor. That is, it is not wrong by 6', but only wrong by 1/2 a foot. I am thinking about roof corners here.
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> When it goes FIXED, usually your 1st fix is bad, because it has not had time to update the computer. Wait for a later fix. IF it goes float, the whole shootin match is subject to question.
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> The DOD Sats that we as surveyors use, orbit the earth about 2x a day. So, there are many combinations possible. If you observe once, and wait 6 hrs, then you are observing with new sats. By doing separate observations, 4-6 hrs apart, then you can develop quasi "Closed Loops" for your observations. This would be good, for extremely important shots. Even waiting 1 hr between shots, develops a good check, but 4-6 hrs is better.
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> OK, tell me yours.
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> Nate
> A study out of the UK showed that 40 minutes was enough change in the constellation that the benefit from more time separation was negligible.
I'd be interested in reading the details. Do you have a reference for the study?
Actually, I'm out solo a lot of the time and all I would have to do is detach the prism from the pole and get the robot to track me to exactly the same position as your mini and take the same shot.
Being solo is no different. A good surveyor is still good and a bad surveyor is still bad.
I'm interested too. Considering the satellites are zooming around on several different orbital planes surely waiting 4-6 hrs is overkill to get a sufficiently different constellation of gps and glonass sats.