I just finished the final analysis of an RTK retracement of a 36 square miles that was resurveyed by an LSLS in 2006. The surveyor does not specifically state what type of GPS was used in 2006 but his notes do mention a calculated combined scale factor, and tying in to an NGS monument which he then adjusted through OPUS.
In general, I am finding most of his called for monuments to be within a hundredth or two of his published location. Except, you know how RTK is, one which is sticking out like a wild hair at 0.12' from the published location. I'm not sure whether to have the crew adjust the pipe with their sledge or perhaps I can review my data and procedures to tighten things up a little.
[sarcasm]Maybe we need to go back to 100% static observations until RTK's inherent problems can be resolved.[/sarcasm]
Mild attempt at humor aside, it was a pleasure to retrace such a large survey and consistently hit the monuments so tightly and so consistently. There were a few pin-cushion corners previously set by other surveyors, but this is in an area where most of the blocks were office surveys laid off from the railroad centerline some 26 miles distant.
> I just finished the final analysis of an RTK retracement of a 36 square miles that was resurveyed by an LSLS in 2006. The surveyor does not specifically state what type of GPS was used in 2006 but his notes do mention a calculated combined scale factor, and tying in to an NGS monument which he then adjusted through OPUS.
I've got to ask how you adjust an NGS monument through OPUS. That must be a beta feature. :>
My composition may be lacking, but my understanding is that he occupied the NGS monument for an unspecified amount of time and then processed his data through OPUS. The answer provided by OPUS was slightly different that the published coordinates for the monument. He held the OPUS solution over the historical data.
> My composition may be lacking, but my understanding is that he occupied the NGS monument for an unspecified amount of time and then processed his data through OPUS. The answer provided by OPUS was slightly different that the published coordinates for the monument. He held the OPUS solution over the historical data.
Okay, so he didn't actually "adjust" the NGS control monument, just adopted a different position for it? That seems reasonable enough.
You'll have to provide more details, though, if you expect the claim that an RTK vector is accurate within about 2mm over 5km to pass the laugh test. That is pretty much what your report of agreement within a hundredth over distances that probably are as much as 5km amounts to, right?
Except, you know how RTK is, one which is sticking out like a wild hair at 0.12' from the published location.
That is just unacceptable:-(
You need to set one in the correct location
Interesting results. When I saw the title of your post, I thought that Kent was going to say that "Busted RTK Survey" was redundant.
I realize that this was what the previous surveyor and not you did; however, I really cannot wrap my head around using an OPUS solution on a NGS marker over the published values. What are your thoughts on this? My premise is that the most qualified/repeatable value should be use. If the monument was knocked out, which value would best fit the survey? If he had a network utilizing 2 or more additional NGS monuments and holding the one monument's value greatly affected the accuracy of the network, I could see using the survey values. If he takes 3 OPUS solution over a few days, I wonder if he would find the published values to be outside a reasonable accuracy.
The reason that I bring this up is I am starting to see OPUS used in urban areas with NGS Monument in some cases in sight. For the record yes guys, I am an over 60 surveyor that has used GPS since the mid 90's.
> I realize that this was what the previous surveyor and not you did; however, I really cannot wrap my head around using an OPUS solution on a NGS marker over the published values. What are your thoughts on this? My premise is that the most qualified/repeatable value should be use.
I realize that you put the question to Andy, but I see the practice as pretty defensible if the network uncertainty of the OPUS solution is lower than the network uncertainty of the published position.
Not all NGS control monuments are really all that excellent and usually all it takes to get a more accurate NAD83 position at current epoch is just leaving a dual-frequency receiver parked on the point for at least four hours while other things are being done. If you're using the same monument as the location of the base receiver on more than one day, you get several OPUS solutions for very little additional effort.
There are NGS monuments and there are NGS monuments, some have been occupied and included in the HARN network, but most haven't, these are just recalculated from record information. They often make a nice spot to occupy but aren't really all that accurate.
This pin is the only one that is correct. I suggest you start over and only use long duration static. 😉
When we go behind most of the people I know, who use RTK, we find very very close results to what is published, typically on a magnitude less than a tenth.
FWIW, I thought your title was hilarious and has, as expected, invoked the desired response.
Now, I predict, as in the past, we will have a barrage of posts over the next week about why RTK should be abandoned and is not a viable tool.
> > My composition may be lacking, but my understanding is that he occupied the NGS monument for an unspecified amount of time and then processed his data through OPUS. The answer provided by OPUS was slightly different that the published coordinates for the monument. He held the OPUS solution over the historical data.
>
> Okay, so he didn't actually "adjust" the NGS control monument, just adopted a different position for it? That seems reasonable enough.
>
> You'll have to provide more details, though, if you expect the claim that an RTK vector is accurate within about 2mm over 5km to pass the laugh test. That is pretty much what your report of agreement within a hundredth over distances that probably are as much as 5km amounts to, right?
So I take it you never actually turned on the RTK feature of that 5700 you bought and ACTUALLY gave it the good old college try then?
> So I take it you never actually turned on the RTK feature of that 5700 you bought and ACTUALLY gave it the good old college try then?
When Trimble specs a horizontal accuracy of +/-(8mm + 1ppm) RMS error for RTK positioning with an R8, what would YOU expect to get out of it? Note that doesn't include antenna centering error, either. This is why a claim of +/-(2mm) activates the laugh function. :>
What makes you think I was baiting Kent. B-)
The NGS Monument was 2nd order horizontal which is 1:50,000 minimum distance accuracy. There is something to be said for planning large control networks and I am definitely open suggestions and further reading. We're really stretching across some large territories out in West Texas.
I had to convert the sketch file from varas and its measurements were in surface units so I additionally applied the CSF to get the linework back down to grid.
I'm having trouble with my control database right this moment so I don't have the particulars on our company control point, but I'm thinking it was an OPUS derived point, too. I did translate the 2006 survey East 0.06 feet which improved the results.
RTK has apparently disabled your ability to inverse coordinates, Andy. Two hundredths? Pfft.
Is that question coming from the same guy that determines his own error estimates for angular accuracy for his theodolites and total stations? Suddenly the equipment manufacturer specs are golden? IMWTK
I know you're not talking about a HARN station, but even if you were, a few days of RTK with the base occupying a HARN monument and you've already got more data than was used for most HARN stations. It could be that the combined OPUS solutions would be more accurate than the HARN coordinates.
> Is that question coming from the same guy that determines his own error estimates for angular accuracy for his theodolites and total stations? Suddenly the equipment manufacturer specs are golden? IMWTK
News flash: GNSS receivers are fundamentally different from electronic total stations and there is no incentive for a manufacturer to underspec the accuracy of their equipment in the top rank. This is quite unlike the situation where total stations are being offered as lesser grade instruments, but with the same circles and centers as are used in high grade instruments.
In general, I am finding most of his called for monuments to be within a hundredth or two of his published location.
Was cannabis involved?
> I really cannot wrap my head around using an OPUS solution on a NGS marker over the published values.
I guess you don't work in California. Our passive marks have significant velocities, and datasheets age quickly around here.
I'm not aware of any HARN monuments in the area.