Almost all of my work is on this island at about 18.3 N -64.7W
My only experience surveying with GPS is using control by others that was presented as survey grade but was really recreational grade.
I would like to be able to establish SPC (PRVI) coordinates for boundary survey control.
Can you offer an opinion of what results I could expect with a single X90 or Triumph 2 unit here for OPUS post-processing with available CORS sites that I understand are less than ideal?
From the NGS CORS map the available stations are about:
24 km. west (2)
55 km. west
70 km. south
70 km. south southwest
170 km. east southeast
Are these useable for control?
With 2 units post processing?
Other suggestions?
Quite usable... Either of the above GPS options will do it.
N
Larry Best, post: 379651, member: 763 wrote: Almost all of my work is on this island at about 18.3 N -64.7W
My only experience surveying with GPS is using control by others that was presented as survey grade but was really recreational grade.
I would like to be able to establish SPC (PRVI) coordinates for boundary survey control.
Can you offer an opinion of what results I could expect with a single X90 or Triumph 2 unit here for OPUS post-processing with available CORS sites that I understand are less than ideal?
From the NGS CORS map the available stations are about:
24 km. west (2)
55 km. west
70 km. south
70 km. south southwest
170 km. east southeast
Are these useable for control?With 2 units post processing?
Other suggestions?
Absolutely they are usable for control. The general idea for static post processing (excluding OPUS) is minimum 10 minutes of observation for baselines under 10 km and 1 minute/km for all baselines 10 km and up, or, for a 15 km baseline, 15 minutes is needed and for an 8 km baseline, 10 minutes is needed. OPUS requires minimum 2 hours (4 hours for the "gold standard"). So, 2 hours would satisfy all of the baselines except the 170 km East Southeast but the 4 hour would meet and exceed that.
In your situation, with two receivers, I would be tempted to let one sit for at least 4 hours and, while that one is gathering data, move the second rover around the site and process it back to the "OPUS Receiver". It would give you survey grade data (since I'm assuming the site is less that 1 km or 0.62 miles big). Each boundary control point you set needs a minimum of 10 minutes. I like 15 but that's me. The control will be tight and related to the NSRS via OPUS. Should work very well and is essentially what we do with a base/rover setup when we run out of radio or I need the control to be exceedingly tight for a myriad of reasons.
[sarcasm]What a terrible place to work![/sarcasm]. Actually very doable. I agree with Kris's post. My next question is how obtainable and open are the positions? Need a clean view of the sky (or the best possible).
Thanks, friends
I don't have any expectation to reduce dependence on the TS, due to the sky view limitations and because I'm too old to trust anything new that much. And I do very few large projects. But I really should provide the best product that I can.
Larry Best, post: 379651, member: 763 wrote: Almost all of my work is on this island at about 18.3 N -64.7W
From the NGS CORS map the available stations are about:
24 km. west (2)
55 km. west
70 km. south
70 km. south southwest
170 km. east southeast
Are these useable for control?With 2 units post processing?
Other suggestions?
The CORS station geometry isn't particularly good, with three in more or less a straight line. You really need the 170km one - I assume that is on Anguilla
Realistically you ought to leave the base station running for as long as possible - 6 hours would be nice. In UK we would tend to use 2-3 minutes per km. as the additional time.
If most of your work is on the island, would it be worthwhile establishing a couple of permanent stations of your own, north and south extremities, so that after you set your base up you then do a short static on one of those with the other receiver, which gives you confirmation that your main base figures are good. Those permanent stations could have been fixed with a really long occupation when you have a couple of spare days.
chris mills, post: 379661, member: 6244 wrote: The CORS station geometry isn't particularly good, with three in more or less a straight line. You really need the 170km one - I assume that is on Anguilla
Realistically you ought to leave the base station running for as long as possible - 6 hours would be nice. In UK we would tend to use 2-3 minutes per km. as the additional time.
Strength of figure, when processing baselines, is irrelevant. This was hashed out and tested with L1 gear nearly 15 years ago and was found to be of no consequence.
PPP = Post Processing P?
Larry Best, post: 379670, member: 763 wrote: PPP = Post Processing P?
precise point positioning, a different way of thinking, and processing gps observables. natural resources canada has a good and free processor.
I can see part of your problem, you do not know where you are. 18.3N -64.7W ????
You are either at 18.3N 64.7W, 18.3N -64.7E or in the Arabian Sea.
More seriously, have you inquired why ABVI is no longer working?
Absent that you need to establish a GPS base station at your office, nothing elaborate and not expensive.
Since your island is only 12 miles across, L1 only is sufficient. What I suggest is you acquire an L1/L2 antenna and permanently mount it at your office. Do at least 3 5 hour observations to establish your coordinates. Leave the L1/L2 antenna in place for commonality of antenna parameters. Before going to the field start a low cost L1 receiver on your base, 30 second epochs is quite OK, then proceed to your project, When you return include your base station L1 data in the post process mix.
I would use a ProMark 2 in the Map 330 automobile bracket, which has a power connection and data port (still available on ebay), feeding the power connection from an AC to 12V DC adaptor.
Paul in PA
Larry, I feel I can comment... Learning GPS. It is hard to figure out where to start. It's hard to go, where you cannot see the road, nor the map.
One time, another surveyor told me, "You should not be allowed to get a surveyors license, until you have worked for at least 3 different surveyors, and understood their practice".
Sort of the same with GPS.
I'd suggest that you figure out how to go and spend several days looking at GPS equipment, and how it all works.
I'd start with whatever Data collector you have. If you have experience with one brand, more than others, then, select a GPS mfr that works with that data collector. This will reduce your learning curve.
I went in the field with 2 different surveyors, watching, and learning, before I bought.
That's just a suggestion.
N
Larry Best, post: 379651, member: 763 wrote: Almost all of my work is on this island at about 18.3 N -64.7W
My only experience surveying with GPS is using control by others that was presented as survey grade but was really recreational grade.
I would like to be able to establish SPC (PRVI) coordinates for boundary survey control.
Can you offer an opinion of what results I could expect with a single X90 or Triumph 2 unit here for OPUS post-processing with available CORS sites that I understand are less than ideal?
From the NGS CORS map the available stations are about:
24 km. west (2)
55 km. west
70 km. south
70 km. south southwest
170 km. east southeast
Are these useable for control?With 2 units post processing?
Other suggestions?
My semi-amateur opinion...if I even understand, is that you might consider setting your own network around the island using found or setting monuments that are point-specifically marked (ie, stamping that cannot me mixed up with other marks), and doing long occupations. I would suggest having at least two points being observed during the same time if at all possible. More if you can swing it. get a good network that is tight unto itself, to make those coordinates fixed. Then, for future projects tie to your local "HARN" (High-Accuracy Reference Network) and hold those HARN point coordinates fixed. If all of your future work is to that same harn, the Global position isn't as important as your local relative positions.
But maybe I'm all wet, since I don't really know what type of projects you do. We have a state-wide HARN network in my state, but it is not used as much as it used to be, with the addition of CORS stations and other means of getting good-enough coordinates.
GPS aside, I'm in love with your island. Been there on vacation many times over the last 30 years. Have seen many changes in Cruz Bay, and more recently in the Coral Bay area. The ex-pats down at Skinny Legs are worried about new marina resorts on the horizon, should work out for you though.
FWIW, when using any of the sutomated processing tools be sure to keep track of reference frames and epochs.
A rather dated example of comparisons between the results of the different tools and issues related to comparing results is here: http://geodesyattamucc.pbworks.com/w/file/fetch/53012749/lab9_2012_summarySolutions.pdf
HTH,
DMM
Paul in PA, post: 379685, member: 236 wrote:
More seriously, have you inquired why ABVI is no longer working?
Paul in PA
Paul, this is the Caribbean. Only half of anything works here. Me included.
I ordered an X-90 yesterday. I'll keep you posted.
The x 90. Is that a Mark Silver i-gage product? And, you only ordered one? Presumably, so you can bring a coordinate down, with a long observation, and, then another, with a long observation?
If you do that, think of a "traverse" that starts at a cors station, goes to your station, then back to another cors station. That's one coord now, based on a long traverse.
Then, repeat.
I'd prefer to see you using a pair of units, and dropping down control in PAIRS , instead of in singles.
It will be a bit more accurate, and you will take 1/2 as long.
IF I'm understanding you correctly...
Using 2 units, (3 is even better) as a minimum, your relative accuracy will be better, and your time factors will be less, and your maximum error potentials will be smaller.
Welcome to the world of GPS.
Nate
Nate, I do understand that 2 units (yes from Mark Silver) may be necessary to make this viable. But I don't know yet how or if I will use this for the kind of work I do. With one unit I can play with it, see if I trust it and figure out how to make it pay.
Try this analogy:
Go by the food bar, get a little of each item of interest. Try it out, then come back, and get alot of what you like. This is what you are trying to do. That's your present game plan.
When, this is more like your situation:
Buy a tractor. And bushog (Boy they are expensive) to cut your field. But, to save money, skip the bushog, and just tie your old push mower to the back of it. Now, you have 1/2 a system. If you like it, you move on, and buy the bushog.
Take my word for it... Get em both, on the 1st go. Cut that field in less than a day.
With your situation, it'll take you a week with your new tractor, dragging the old push mower, and you don't get full benefit of your tractor.
Get 2 units. With rtk.
I'm a Javad user, and fan. But for you, any tractor and bushog is better than that push mower!
Best GPS to you.
Nate
So now I can determine SPC and elevation with the X-90. This forum and Mark Silver have been great.
My next questions are:
When other surveyors record a map when SPC have been determined, do you necessarily put that information on the drawing?
If not, why not?
if so, what metadata do you include?
Larry Best, post: 390950, member: 763 wrote:
My next questions are:
When other surveyors record a map when SPC have been determined, do you necessarily put that information on the drawing?
If not, why not?
if so, what metadata do you include?
Regardless of the tools used I think you should recite the metadata of the two (or more) monuments you used as a base. Name, source, record NEZ, SPC version, epoch, physical description, etc. That gives us a fighting chance to recreate your work. If using COORS then just repeat the metadata from your report.
A simple small scale sketch of the control ties are also nice, kinda like a location map.
When I see "SPC Zone 12, measured with "xxx" on January 12, 2007" I go WTF?