Mike, I know the point I chose isn't useful for the GPS on BM program, but I needed some points to practice on, including the submittal to OPUS Share. Once I saw my data, I knew it was crap, but I wanted to see what sort of techniques I could use to de-crappify it. Otherwise there's no way I'd go near anything like TEQC, which feels like the nightmare days of DOS.
I'm aware of the multicolored geoid map showing what areas are lacking in coverage and I've identified a number of locations I want to bag in the California deserts this Fall. In those cases they are specific BMs that will be useful to the geoid effort. If I don't screw it up. Hence my current flailing around. With time, the flailing should subside.....
Tom
OtherHand, post: 446241, member: 12932 wrote: BushAxe, I'm doing this stuff as a rather strange hobby, submitting under the GPS on Bench Marks program. Ultimately I'm planning on submitting on some BMs in lacking areas that will feed into the new Geoid model. Before that though, I need to figure out how to do all this stuff. As part of my learning process I selected a number of fairly uninteresting BMs to do dry runs on, including the submission process to OPUS Share. The main criteria for me in selecting these trial BMs was that I could drive pretty much to them, and they needed to have a high elevation since, you know, it's hot out now. If I have to sit on my ass for four hours I want to have a nice spot! When I picked this spot online I didn't realize it was now under a tree. Once I actually saw where it was I thought it unlikely I'd get good results, but as part of the learning process I needed to see just how bad a configuration like that could be. Now I know. Pretty bad.
Gene, thanks so much for that explanation on CORS quality. It was really helpful. I'll pull up some more CORS sites and have a look at them now that I know what to look for.
Tom
I'm tracking you now. I just wasn't understanding why you were insisting on that particular point. Now I get it.
Sent from my iPhone using Tapatalk
I'm doing something similar and have submitted several OPUS shares. One is a nice gap filler, and others are less important.
I started testing with a local HARN station (did not do a share) to prove I could get within a cm or two. Also checked and shared on one our DOT had shared before I branched out to marks that had no prior GPS data.
My most recent was more of a commemorative effort than for important data. See my thread Pictures from the Field.
I'm assuming the programs can eliminate bad data from inclusion into geoid model improvments.
But only good NAVD88 bench marks are useful for that.
Bench marks that can be verified as still good by checking to other existing ones.
Otherwise the data submitted would tend to distort the Geoid.
Be careful what bench marks are used, without knowing they are still good they can be more harmful than helpful.
MightyMoe, post: 446253, member: 700 wrote: Be careful what bench marks are used
I'm pretty sure the GPS on BM project will only use shared data for marks that have good quality NAVD88 data.
The bench marks I'm interested in are shown onhttps://arcg.is/1Xiaue&apos ;"> this web page in the yellow and red areas. NGS seems pretty clear which bench marks would be useful to them and which have no priority so I hope not to screw that up. It's a much smaller subset of ALL the bench marks shown on the NGS Data Explorer map. Since most of the locations I'd like to do infill in are in the middle of BF nowhere and require considerable time/effort to get to, I want to make sure I know what the hell I'm doing before I head out (as if that's stopped me before). In truth, this is just another semi-plausible excuse to go on wild goose chases in the middle of nowhere. Since you guys actually get paid for this sort of stuff, I guess that makes me a special kind of stupid....
Tom
Bill93, post: 446261, member: 87 wrote: I'm pretty sure the GPS on BM project will only use shared data for marks that have good quality NAVD88 data.
How can they know if a first order mark has moved?
MightyMoe, post: 446263, member: 700 wrote: How can they know if a first order mark has moved?
That's an excellent question, and I don't think anybody has a good answer for it.
Loyal
Tom, I commend your interest in helping to improve the hybrid geoid model. I am glad you clarified that you understood the point you observed was not suitable.
As I am unclear about your familiarity with making GPS observations, I expect you recognize the importance of the integrity of your setup and measurements to determine the antenna's height above the monument. As the disclaimer on OPUS solutions indicates, solutions are only as good as attention to being accurately set over the monument, identifying your antenna model correctly and measuring to the ARP accurately.
When it comes to how "they" know if a first-order (or any) monument has moved, it is by performing ties to other monuments.
In traditional optical leveling the specifications require leveling to other equal or better order of accuracy bench marks. If checks are within tolerances, this indicates the point remains valid. Unfortunately many practitioners do not often perform these checks. BTW, checking between a monument its reference marks or other closely spaced points is not adequate. See FGCS leveling specifications available on the NGS web site.
All monuments are suspect until validated. In fact, continuously operating GNSS sites are validated on at least a daily basis by processing against other sites in the network. It was surprising in the early days of the NGS CORS that many site operators would make changes to their sites without passing on this information. Replacing a rusted bolt, a replacement of a guy wire, etc. would be revealed by network processing. It would lead to a call to the site where they would usually say they thought they put the antenna back where it was.
MightyMoe, post: 446263, member: 700 wrote: How can they know if a first order mark has moved?
I think the geoid guys want data in some areas to validate suspected movement. I'm in a known subsidence area that began showing up as such as early as the late 1960s. One if the desired BMs is on one of those lines, and I assume they'd like to have it to see if it checks with other work.
Jim Frame, post: 446275, member: 10 wrote: I think the geoid guys want data in some areas to validate suspected movement. I'm in a known subsidence area that began showing up as such as early as the late 1960s. One if the desired BMs is on one of those lines, and I assume they'd like to have it to see if it checks with other work.
It??s ultimately up to the submitter to choose wisely.
I would think most surveyors have a good handle on the quality of the bench marks in the areas they work. It??s almost impossible to spend time surveying without knowing if the benches check between each other in the areas you work.
I would think most areas have lost a number of bench marks, of the remaining ones some will be unusable as GPS points (vertically set into the side of a building would be one example).
A percentage will visibly look ok but will have been disturbed in some way, either by construction or settlement or something. I would put that number at 10 percent or more. If a bench is along a railroad near a county road crossing and they did an improvement of the crossing it may be that it was removed and reset by a contractor.
Stuff happens. I know of 4 railroad bench mark that were moved.
It??s easy enough to be sure if one was disturbed by checking between it and other nearby ones. Then you can have confidence.
I don't know the process NGS uses to accept data for adjusting the GEOID model. Is there some way the information is checked? How can anyone see that a bench is .3' too low along a railroad when the next submission is from 10 miles away. Will that disturbed bench be included in the GEOID adjustments? Or will it be excluded even when it shows on a datasheet as a first order stable bench.
With canopy like that you'd best call Nate, use his Javad LS. He'all get better results than OPUS.
:yum:
Bad positions can come from very good data observations. When you look at the data satellite by satellite, the observations may be good, but if particular satellites are blocked the observed position is bad. A strong observation requires a spread of satellites throughout the sky. Even just the blocking of one satellite in a an area can allow the resolved position to skew towards the good observations. If satellite signals get through and are then blocked in a cycle, the position dithers here and there.
The best you can do without removing trees is long observations at various times of the day. Since this is a learning experience do not give up on this position. You will probably never get apple pie, but you may get pretty good apple sauce or maybe just cider.
Paul in PA
MightyMoe, post: 446253, member: 700 wrote: Otherwise the data submitted would tend to distort the Geoid.
It's my impression the new geoid will be entirely determined by data NGS collects itself through GRAV-D and some of their other data, and the GPS on BM data will only be used as a check to signal them of problems in their own data. One example might be finding the need to collect denser data in some area, because the check data from multiple points in an area indicate a trend departing from their preliminary models.
MightyMoe, post: 446219, member: 700 wrote: I really don't think anyone wants a tree cut down just to get a GPS shot, private or public lands.
I know this one guy ...I like to bring him along from time to time...
Bill93, post: 446294, member: 87 wrote: It's my impression the new geoid will be entirely determined by data NGS collects itself through GRAV-D and some of their other data, and the GPS on BM data will only be used as a check to signal them of problems in their own data. One example might be finding the need to collect denser data in some area, because the check data from multiple points in an area indicate a trend departing from their preliminary models.
That's my understanding also.
In a couple of years the "official" Geoid will be all changed.
However, it will be many years until NAVD88 goes away, FEMA maps and historical community mapping will not just vanish.
FEMA is as much a political process as it is an engineering process. If the last set is any example there are some very tender feelings in some communities which will be difficult to overcome. They really need to step up their game, if they do some of the things they did this last time around, nobody will vote to accept the mapping.
MightyMoe, post: 446284, member: 700 wrote: How can anyone see that a bench is .3' too low along a railroad when the next submission is from 10 miles away.
In my area they're not looking for tenths, they're looking for a meter or so.