> What do you mean by sun shot?!? The control points were RTK.
He means taking a solar observation with your total station about every mile or so as you traverse. It will help.
> > What do you mean by sun shot?!? The control points were RTK.
>
> He means taking a solar observation with your total station about every mile or so as you traverse. It will help.
If you need a Sun Shot, why bother with GPS?
Ralph
> I am using a Trimble R6 using TDS Pro to set control points at the beginning, middle and the end of a job. The total distance of the job is 5 miles. After setting these 6 control points with GPS I am currently running a traverse between them. I am half way through the traverse and when i came up to the middle set and missed the points by .45 on the northing, .25 on the easting and .44 on the vertical. Is using the GPS in conjunction with the total station the right procedure when known points aren't available?
>
> Thanks everyone in advance for your help 🙂
Some other things to consider:
Are you using a 1", 3", 5" or 10" total station?
I assume you are taking at a minimum Forward, Reverse, Reverse, Direct observations for each traverse point. If you want to tighten up your traverse work, add more sets.
Do you see any abnormally large residuals on adjusted angles in your traverse (assuming you are using least squares)?
Lots of factors to consider here.
I hope this helps.
EDIT You can find some good information here. I am not sure if this is pertinent to your project or not, but some good food for thought anyways.
That's an easy one...
My money is on Loyal. More detail is needed to find the source of the problem. Separating the collection of RTK on the same point on a different day at a different time of day, say by at least 4 hours, could remove multipath problems but it does not have to be the case that multipath could be removed in this fashion, but it usually works well.
I don't know the type of work he is doing, but I do know that adding some solar observations, with static GPS control, and traverse lines gives some redundancy when using Least Squares. It can be enough to get through the first iterations.
> I don't know the type of work he is doing, but I do know that adding some solar observations, with static GPS control, and traverse lines gives some redundancy when using Least Squares. It can be enough to get through the first iterations.
It wasn't intended as a flame, I just think that a Solar defeats the purpose of GPS. In my opinion GPS is meant to replace it. I'm just curious how you would weight this scheme.
Ralph
> I just think that a Solar defeats the purpose of GPS. In my opinion GPS is meant to replace it. I'm just curious how you would weight this scheme.
Although I haven't turned a solar in about 30 years -- GPS observations have made star shots unnecessary in my work -- I can see how good use can be made of them on certain projects. I don't expect it's very difficult to come up with a standard error for a solar observation, which would make it easy to include in a network adjustment.
>It wasn't intended as a flame, I just think that a Solar defeats the purpose of GPS. In my opinion GPS is meant to replace it. I'm just curious how you would weight this scheme.
>
> Ralph
No worries Ralph. I didn't take your comment as being argumentative at all.
I just know of several different privately and publicly employed cadastral surveyors that still use solars.
I agree that GPS is by far the more commonly used method. Redundancy never hurt a survey, maybe the budget...
For what it is worth:
For hour angle method, I would probably use a method similar to this example:
> No matter the brand of GPS or Total Station, I highly suspect you have some bad GPS data.
>
> That being said, I hope you have checked your total station and GPS against some proven baseline before this job was started.
>
> A simple check will head off a complicated problem.
>
> Randy
Always worth heading to a calibrated baseline!
That's an easy one...
I am on long island,ny doing a topographic survey of dune road which is very close to the water at elevation 2.0-6.0. There in no overhead obstructions other than minimal overhead wires. Our procedure was we fired the rtk gps up in NAD 88/83 and located 3 sets of 2 control points at the beginning, middle, and end of the job for 3 minutes each over the period of 4 hours and took an average of the 3. Then we set on the first set on the west side of the job and they held within themselves. We traversed up to the middle set shooting roughly 700 feet in between each point turning two sets of angels. When we got to the middle set we missed the northerly by .45, the easting by .25 and the vertical by .45. on the first point of the second set and the second point 700 feet away we missed it by .54 on the northerly, .33 on the easting and .54 on the vertical.
I am using a 3 second Leica total station. I am not currently seeing any large residuals.
do the easy checks first...
I would check all the level bubbles in the gps and the conventional gear, if you haven't already.
then I would consider re-observing the control points to verify the GPS portion.
if that all checks, then the problem is in your traverse.
> >It wasn't intended as a flame, I just think that a Solar defeats the purpose of GPS. In my opinion GPS is meant to replace it. I'm just curious how you would weight this scheme.
> >
> > Ralph
>
> No worries Ralph. I didn't take your comment as being argumentative at all.
>
> I just know of several different privately and publicly employed cadastral surveyors that still use solars.
>
> I agree that GPS is by far the more commonly used method. Redundancy never hurt a survey, maybe the budget...
>
> For what it is worth:
>
> For hour angle method, I would probably use a method similar to this example:
>
>
Thank You Kevin,
I would maybe do it a little different, probably formulate some sort of variance matrix and take the partials. But it's not my point of contention.
Here's how I see it (I could be wrong and it wouldn't be the first or the last time, but I find I tend to learn stuff this way)
A)He has questionable GPS coordinates, which could probably serve as an initial approximation
B)He has a questionable traverse (not sure what his procedures were)
C) I haven't done a solar in a long time, but if I recall you have to set up on a known point. Would this point be based on, his questionable coordinates?
I see this as an opportunity to introduce more uncertainty to an already confusing situation.
I wonder what it would look like if he did a free adjustment based on his traverse data.
I would think the prudent thing to do would be to sit back, study his procedures, check his equipment and re-observe it all using better techniques. At that point the source of his error will probably stick out like a sore thumb and he'll report back and maybe we all learn something.:-)
Cheers
Ralph
That's an easy one...
Are you comparing these coordinate values as SPC or to a local datum? Those departure values seem excessive for just a scale factor bust...
That's an easy one...
Then we set on the first set on the west side of the job and they held within themselves.
What does this mean? The distance checked?
Ralph
Andy provides valuable advice...when troubleshooting survey data the simplest issues tend to cause the most problems. They are also the easiest to check and to fix.
Thots:
Check your ppm on the TS.
Check your prism offests.
Check your tribrachs.
Check your rod bubbles
Check your environment for multipath. IF you Re shoot with rtk, at about the SAME time each day, you can duplicate the multipath error.
N
That's an easy one...
Oky doky:
I'm a little fuzzy on just what this means (see below).
“...we fired the RTK GPS up in NAD 88/83 and located 3 sets of 2 control points at the beginning, middle, and end of the job for 3 minutes each over the period of 4 hours and took an average of the 3
I will ASSUME that it means that you started on a station with a KNOWN NAD83(xxxx) Coordinate, and NAVD88 Height, and further ASSUME that you took three (3) ONE MINUTE observations on each of your six traverse stations. It could mean something entirely different I suppose, but we'll start from here anyway.
First...I would never use RTK for “Control” in this type of situation, BUT I do know some folks who DO, and they get some pretty good results. The big difference that I see between what you did (or I assume that you did), is that they use 5-15 (or 30) minute “RTK Infill” shots (a Trimble term I believe), AND they perform multiple observations (run South to North, and then repeat). They also push the backsight points out closer to 500 meters (or more), but you may NOT have that option.
Now the “traditional rule of thumb” on RTK shots, is about +/- 0.010 meters (a centimeter), and in my experience that is pretty reasonable, even at 2 sigma (ASSUMING all is well). With a 700 ft. (~215 meter) backsight, that COULD mean an angular error of 15-20 arc-seconds from the get-go. Lets face it....you could have .010 meters one way on the Trav-station, and .010 meters the OTHER way on your backsight 700 feet away (it happens). That could throw you 1.23 feet in your 2.5 miles right there!
You didn't post anything about what your linear inverse between Trav-1 and Trav-2 were (RTK v. Total Station), but I would start there. IF (big IF) you are seeing something like 0.10 FEET (or less), then I would strongly suspect a rotational problem caused by the “iffy-ness” of your RTK solutions between your Trav-Station(s) and your backsight(s).
Now all of this ASSUMES that you are making the proper environmental corrections (temperature & barometric pressure) at the Total Station, have NOT done some lame-o “calibration” to the GPS data, HAVE used the same coordinate system/projection in both data sets, AND made SURE that your tribrachs, rod bubbles, etc. are in CORRECT adjustment.
All in all...700 foot traverse legs are kinda short, so forced centering would be a MUST (IMO), and 1:25,000 wouldn't be that big a deal back in the “OLD DAYS.”
Given 4 hours, and two receivers, I would have opt'ed for a modified leap-frog static (or fast-static) approach to the problem. That would have given you a LOT more data to play with. Of course the REALLY HOT SETUP, would be to have 6 receivers and then you would be walking in tall cotton!
Loyal
Sounds like a good plan Ralph.
Identify blunders and remove them from the control network.
Once blunders are removed, perform a least squares adjustment on the redundant control network.
I have used RTK and traditional traverse together like this in the past with good success. Without having much information here I wouldn't be surprised to see that kind of error in 2.5 miles if you held a pair of RTK points at the beginning of your traverse and then traversed that kind of distance. It's probably a rotation error, I would align the first and last traverse point to your first and last RTK control point and see if things tighten up. I doesn't take long to build up some rotational error in a traverse holding two RTK points at the beginning. The best RTK points usually have at least .05' .10' of error in them and can build quickly when traversing off of them. As a rule of thumb I don't like to through more than one traverse leg off of a pair of RTK control points unless I have something set up like you described where I have in the middle and end and can re-align my traverse as needed. I would first do some inversing to make sure the direct distance between the control compares tolerably with the traverse, if they don't compare well you have a scale factor error or other error.