GNSS, trees, assumptions
:good: 😀 Funniest thing I have heard all day. Because I can see the picture in my head of some field crews trying.
Jacobs staff and Gunters chain.
I use GPS in conjunction with a ground survey for property line, but I have a problem coming up in the near future.
I found an ancient ring of stones located about 1,000 west of locus. Given the limited amount of monumentation and no occupation, it has become a critical monument in my boundary analysis. I located the ring with RTK in the fairly dense woods several times on two occasions.
This ring of stones was at the northerly end of a 25 rod line with two piles of stones located 15 and 25 rods to the south. I located each of these on two occasions in the fairly dense wooded area with RTK.
A surveyor erroneously placed the two parcels located to the west of the 25 rod line so they overlapped the 25 rod line by 70-100'. He held the wrong point of beginning and a deed distance. He did hold the two obvious piles of stones for line... He created a division and the lot with my beautiful ring of stones was developed.
When they cut down the trees on this lot, I happened to find out that I had a very small window of opportunity to locate my beautiful ring of stones. I again located the ring with RTK and a large view of the sky.
All the locations fall within 0.10' of each other.
There is nothing else to rely upon other than a series of RTK shots. My plan will contain a note regarding the destruction of this essential monument and the methodology I used.
During these reconn sessions, I did find another ring of stones that I located in the dense canopy twice. The multiple locations on the same day were similar, but the differences between the different days was about a foot. No complete reliance can be given to the RTK locations until a ground survey either proves one or neither.
Best ring of stones I ever found.
Facing ESE:
Just like the post about setting 3 control points over 2: If I set a bound with GPS, I will start by setting 3-4 hubs and tacks around the bound point. I will locate these with a horizontal tolerance of 0.01'. I will measure between them and list the inverses. If they do not check well, I will do it again.
Avoid the woods. You will not get the results you want as often as you want them.
I used to take a tape with me(doing RTK), set 2 nails, then set the RTK on the pin.
I would record the RTK position(s), while also gathering static data.
Since this was way out in nowhere, I'd let it cook for a good 1/2 hour or more. In fact, I'd often leave after a few RTK readings and look for the next pin before coming back to record a few more RTK readings In the spring, I'd often just lay my coat out and sleep for a while.
Then I'd move the RTK to the next two nails, also getting static data.
I had already measured the distances between the nails and the pin . . . a triangle with about 20' sides.
If everything worked out with the RTK positions between the 3 points, I'd call it good and then check the static data to see if the static data gave me the same coordinates.
If it didn't work out . . . oh well
Nice stones!
I located a stone ring just before christmas.
This is what it looked like:
It wasn't described as a ring, but as a mound of stones. Someone had scattered them into a ring.
Nobody mention scale factor?
Unfortunately no. Otherwise I'd be happier to publish a GPS coordinate on a plan. I had a very little window one afternoon with other commitments limiting my time. Someone forgot to dump the base from the previous job before rushing out the door. I am not sure who that was, but he's been properly scolded. They excavated the next morning.
linebender
I have upgraded to a solar transit and a 8 chain tape!
linebender
You BLM guys always get the fancy stuff.
Line Staking
A very good point. Before you rely on new equipment or procedures, compare to existing equipment and procedures. Compare the qualities of relative mons in your history that were righeously closed conventionally. Hit some points with narrowing sky patterns to compare.
If it was me and I wanted to add GPS as a tool to enhance future efficientcy, I would schedule a full day in the field to orient everyone to use of the new equipment. It's just a day of testing not different than a yearly exercise at the nearest Base Line to verify YOUR foot.
Hit a point just next to a building and see what you get. One day of testing is going to orient you to what is acceptable with your gear.
If you have a client with 3 or 5 sections of ranch lands with lots of canopy, use the GPS to establish control in the vicinity of your traverse to tie in where efficient to do so. A half hour spent thinning even if open sky is hard to come by. Just 4 or 5 GPS points will resolve the work into 1 or 2 mile pieces of traverse.
If you get a closure of a foot in 10,000, is that a one foot bust or random error? In a ten mile loop you can't certify whether good closure numbers and standard adjustments don't have a bust that is hidden. Breaking it down into good GPS points along the project puts error analysis behind you.
Explain to the client how a days labor of a timber faller to make a few holes in the canopy at the right places will save him lots of money on the survey. Certainly more than the labor of the faller will cost.
I'll answer the questions but will first qualify myself as using 3 different RTK units (brands) in the last 12 years, the first two base-rover systems and the current being a network rover. I will also say that most of my work is marking lines for cutting for our Forestry department but it still can be considered boudary survey work, as I do set monuments and create final maps.
> 1. Is it accurate?
Yes, but don't trust one shot - one initialzation.
> 2. Are the readings repeatable?
Yes, but don't trust one shot - one initialzation.
> 3. How consistent is the data?
VERY good for what I use it for.
> 4. Can you replace property corners with any accuracy?
yes, with time, patience and checks
> 5. Is this a magic box?
Yes, for me, until we have CM accuracy on cell phones in 7 - 8 years.
> We have a Trimble Pro XR that is over 10 years old that we use for wetland surveys and I have seen it get to within 1.0 feet with shots and they are repeatable if you use the correct methodology (shoot the same control points before each session and post process the readings just to name a couple).
Very good statement in there! I mentioned using 3 different RTK systems. I had to develop my own methodology for each system - so I knew the limitations of each. Not all GPS equipment works the same! All can give bad results.. its up to the user to come up with methods to catch those 'bad' points.
I mentioned I do work for our Forestry Dept. Because of certain seasonal factors, at times they need boundary information real quick. For example, they were recently informed of an upcoming winter cutting on private lands that adjoin a landlocked county parcel. It is 'landlocked' by swamps, creeks that don't allow access. Winter logging jobs HAVE to happen because swamp roads can be frozen to allow for the heavy equipment to get to the wood. The logger said he would cut the county parcel (which was overdue for cutting) next week if the county would put the line in this week. It is very easy for the logger to get to the County land through the private land because he already has frozen access roads created. So yesterday, I went with one of our Foresters, located the last quarter corner I needed to compute the section, and then accurately marked 2,000 feet of boundary line - all in 6 hours with the network rover. Had I told him it would take two guys, three days using conventional methods, they would have said forget it.
I didn't set two interior 1/16th corners. When the wood is gone in a couple weeks, I will set monuments, and at that time can also set a couple check points out in the open where the wood was yesterday.
Static might work under canopy. I used to collect static data for 2 hours or so and than process first half and the second half of the raw data and compare two vectors. Splitting gives some sort of in dependency.
I did so because I did not want to traverse all way back through the woods, and I was closing to GPS point ok, I noticed poplar trees are bad for GPS signal but in spruce I was getting better results. it was saving me a lot of time.
linebender
As long as you put it on the latitudinal arc then it is good.
linebender
Yes, staying ahead of the curve on technology!
Yes, very accurate providing you have a 150' rod w/ a 10" bubble and use a big (really big) bipod.
Alternatively, I've had mixed results using a large balloon and really long plumb bob.