The surveying we do has very loose tolerances compared to what most of you do. Generally speaking submeter is good enough for us. A Trimble R8 GNSS RTK system is the only tool we have at our disposal.
On a recent project I had a 4-5 points that due to buildings, trees, etc I could not get a fixed solution even after standing there for 15 minutes. I ultimately just stored the float and then adjusted the elevations to the adjacent points which were less than 100' on either side of the the bad location. In this area there is less than 3' of elevation change in a 1,000' so I felt ok on the elevation and the points are in a straight line so I made sure the X,Y jived and it did. Worked for my purposes but I know it would be a no go in "real" surveying. Of the 4-5 float points I stored most were within 4' of what I believe to be the correct elevation but two were really off. The elevation was around 7' and they stored as 32' and negative 6'.
What can I do if I encounter this in the future? I have never used the static or fast static methods of surveying and am not even sure I understand how they work. If I am in a bad spot can I set up the instrument for a fast static / static and let it set there for a longer period of time and get better results that way? Again my results really only need to be submeter.
Are you using Trimble Access? You could try different collection techniques, but probably the single biggest thing I would do, if possible, is revisit the point(s) in question several times over the course of the day. It would be pretty unusual for an R8GNSS system no to be able to get a fix at a point under any circumstances. You could look at the results of several occupations; even if they were float solutions, if they agreed with each other at a tolerance you can live with you could average them.
Another option would be to use WAAS but the vertical would be pretty bad, and you'd have to change the coordinate system.
Where is your base set up? Does it have clear sky and no interference from things like high transmission lines? Any of your error budget that is used at the base is not available at the rover.
You could also use the offset functions in COGO; walk out to where you CAN get shots and do some kind of intersection. I prefer distance - distance if I can get two points with an intersecting angle between about 60 and 120 degrees - 90 of course being optimal.
Lee gives you good advice.
One more option. Straight line offset.
This is where you flag your point of interest. Find a long straight open path, from the monument, to an opening.
Then, set up your GPS so you tie 2 points, in a straight line, with your point of interest being the 3rd point. Then, tape your distances. Monument to GPS 1, gps1 to GPS 2.
GPS 1 to GPS 2 is a check.
Then do elev. With a hand level.
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I know nobody does it anymore, but mission planning might help.
Sometimes a 15 foot range pole helps to get over buildings or trees.
Forget static and fast static. And standing at the same spot longer will not make reception better. Set the record time in the options to 1 second, to be sure that measurement is quick. Go to an open spot a few meters away and wait for your fixed solution. When you have it, move quickly to the point you want to record and hit measure. you will loose accuracy while moving quickly, but it will be sufficiant for what you need. This is a trick that might not work that good with older R8 receivers. I used it with a R8 Model 2 and a R8 Model 3.
