i'm flabbergasted

Is that a LEica?

Are you saying that Leica is as good as Javad?

N

Are they really that good? What kind of cover do you have in TX? I just ordered one of the GS14's. Should be here next week. Nice 0% financing available, too 24 months.

> Is that a LEica?
Yup. GS14 is a Lieca. I had a demo, nice little unit.

Yeah, it's the leica network rover. I can't speak to current javad- the stuff I used was 10 years ago, before my decade as an office rpls.

Cover on this job isn't TOO bad right now, we've lost some leaves, but I was down in the creek all day yesterday (-30'), surrounded by trees and condos, and never had fewer than 15 sats available.

I Doubt That 15 Satellites Were Used...

...without looking at your actual data, 15 could easily have been available, but the nunber visivle and useable is probably far less.

Unless you break out a total station and check your work you will never know how bad your data is until you lo$e in court.

Paul in PA

I Doubt That 15 Satellites Were Used...

Or he could just come back 4 hours later and re-observe some key points to make sure they are within his error budget. RTK isn't some mystical magic tool that has to be checked with a total station. Keep an eye on the number of SVs being tracked and PDOP and do frequent check-ins to control points. [sarcasm]Or break out the T2 and invar tape and check everything.[/sarcasm]

I Doubt That 15 Satellites Were Used...

:good:

That's what we run. They are quite nice. I still think the Trimble R8 was just slightly better for shooting things in tight places.

You also have to remember that it's not just whether or not it gives you a solution, it's how good that solution is. Checking the values against some total station data is a good idea if it's possible or within the budget. In this case It may be a good idea since you are ahead of schedule already.

Checking it a second time with the GPS would probably be just as good.

I Doubt That 15 Satellites Were Used...

This is the right idea. Just dump the antenna and take the shot again. If it agrees, you're probably golden.

The four hour separation idea is something the UK survey association debunked a few years ago with empirical data. It's more like 40 minutes. But, if you dumped the antenna, moved 15 feet away, then came back to the point and it agreed, I'd be satisfied.

> Or he could just come back 4 hours later and re-observe some key points to make sure they are within his error budget. RTK isn't some mystical magic tool that has to be checked with a total station. Keep an eye on the number of SVs being tracked and PDOP and do frequent check-ins to control points. [sarcasm]Or break out the T2 and invar tape and check everything.[/sarcasm]

I Doubt That 15 Satellites Were Used...

Do you have a link or other specific info about the UK report? I'd be interested in reading it.

I Doubt That 15 Satellites Were Used...

www.ncl.ac.uk/ceg/research/publication/138782

I Doubt That 15 Satellites Were Used...

> www.ncl.ac.uk/ceg/research/publication/138782

This is old news, hereis the TSA
reports

TSA Guidance

ReObserving With RTK Will Show Repeatability, Not Accuracy

These observations where made under canopy and with building obstructions. With a reobservation the satellites may move and may in fact be different. However the trees do not move nor do the buildings. You may have the same poor satellite geometry due to obstructions which accomodates a matching repeatable position but not neccessarily a precise one.

I have done GPS in urban canyons and have even had static solutions that differ from reality in excess of 10 feet.

Paul in PA

I Doubt That 15 Satellites Were Used...

yes paul- i understand that we, as surveyors, tend to take a first glance at anything with less than fully faithful eyes, but...

i do understand how rtk works, and what the difference between the number of available satellites and used satellites is.

i also understand that without repeated checks with conventional instruments against known control, one can have an entire job be correct relative to itself only.

if i told you i overlapped every control point i set multiple times with the robot, and checked into 4 city control monuments each day of work, as well as several control points set by others on adjoining projects, would that suffice?

i'll gladly sign my name to this work- i have absolute faith in my procedures and the data that results from them.

my only point was technology has come a long way. i know it's old news for some of you- for some of us, not so much.

here's the final set-up from this morning- had to fill in that opposite site of the creek (where 3-4 feet got washed out in a flood last month). there were a few spots where i was sure i was gonna be buried in a landslide, but nada.

oh, you can't really tell from the picture, but there are enough clothes hanging from the trees and roots to stock a goodwill, maybe two.

ReObserving With RTK Will Show Repeatability, Not Accuracy

Paul, I agree RTK under tree canopy and next to buildings is high-risk.

However, the likelihood that you will fix precisely and inaccurately among epochs in that environment (on the premise that buildings and trees don't move), is immeasurably small. I'm referring to the antenna dump technique, moving 15 ft and then reoccupying.

> These observations where made under canopy and with building obstructions. With a reobservation the satellites may move and may in fact be different. However the trees do not move nor do the buildings. You may have the same poor satellite geometry due to obstructions which accomodates a matching repeatable position but not neccessarily a precise one.
>
> I have done GPS in urban canyons and have even had static solutions that differ from reality in excess of 10 feet.
>
> Paul in PA

I Doubt That 15 Satellites Were Used...

Free version of paper:

ftp://stella.ncl.ac.uk/pub/pjc/offprints/Edwards_etal2010.pdf