Interesting. I was under the impression that the passive network would not longer be updated as the connection would be made by most with gps. I wonder if light squared has anything to do with this change.
Kris
I don't believe that Lightsquared had anything to do with it at all.
There have been informal discussions floating around about a "ReReAdjustment" ever since the 2007 Readjustment was published.
My take on it is that this program was undertaken at the "Popular Request" of the NGS Stakeholders and Partners.
I think that it's a GOOD thing, and in some ways almost inevitable.
Loyal
Kris
I agree. Lots of folks still use these marks. We dont. Opus is always close enough for the vertical work we do. No projects I work on require absolute elevations tied to passive marks.
It is nice that the new values on the passive marks will equal the Cors 96 epoch 2002.0 (nsrs2007).
Well actually NO...
"It is nice that the new values on the passive marks will equal the Cors 96 epoch 2002.0 (nsrs2007)."
The 2011 Readjustment of the Passive Network, will be done inorder to align (as nearly as practical) the Passive Network to NAD83(2011) which is the NEW CORS Realization to be released in July. The Epoch will be 2010.000 (last I heard).
Loyal
Well actually NO...
The reason I said that was due to some literature that I read saying that CORS96 (Epoch 2002.0) for us, was equal to NSRS2007. I hadn't seen anything on my OPUS about CORS2010.
I'll check it out, thanks for the heads up.
Kris
With the notable EXCEPTION of Arizona, California, Nevada, Oregon, Washington, and Alaska...NAD83(CORS96) Epoch 2002.0 is essentially equal to NAD83(2007).
As it now sits, some of NAD83(2007) is expressed at Epoch 2007.0 (the six states above), and the rest of CONUS is expressed at Epoch 2002.0000.
So within MOST of CONUS, you statement is true TODAY, but that isn't where the new realizations are going.
When the Multiyear Solution of the CORS (NAD83[2011]) is released in July (beta data available now), NAD83(CORS96) will go the way of NAD83(CORS94), and NAD83(CORS93).
NAD83(2007) will be replaced by NAD83(2011) sometime around the first of the year. As with the last readjustment, NAD83(2011)[CORS] will probably NOT = NAD83(2011)[Passive] EXACTLY...but it will be VERY VERY close. AND...both realizations will be expressed at the same epoch (2010.0000)
Loyal
I wish they would readjust ALL of the passive marks, not just the GPS'd ones. One might argue that the change in position is less than the accuracy of many of those stations. But, my belief is that having a lot of high accuracy GPS positions on older marks that are part of the conventional network just makes the conventional network all that much stronger (i.e. helps to remove scale and azimuth deficiencies, and controls "position creep"). In the future when we transition to a "more earth centered" reference frame, it appears that all of the 100's of thousands of non-GPS passive marks will be left behind. I maintain that they have their usefulness, and it would be nice to have updated positions on all of those as we go forward. Many surveys not in the NSRS done in the past could be updated by readjusting using the updated positions. Not quite as accurate as a new survey, but often good enough.
""" In the future when we transition to a "more earth centered" reference frame, it appears that all of the 100's of thousands of non-GPS passive marks will be left behind. I maintain that they have their usefulness, and it would be nice to have updated positions on all of those as we go forward. Many surveys not in the NSRS done in the past could be updated by readjusting using the updated positions. Not quite as accurate as a new survey, but often good enough."""
might be good to have a full adjustment to passive marks as well, considering the future problems we will have courtesy of Lightsquared.
Mike Potterfield has characterized the USC&GS/NGS Passive Network (Horizontal & Vertical) as a “National Treasure,” and I agree with that comment 100%. I would also include the USGS Passive Monuemnts in there too.
Ideally “we” (the Private Sector) would band together at the State or County Level, RECOVER these monuments, and perform OPUS_DB observations on ALL of them. Well...that ain't a gonna happen in very many cases, and once that they are gone, they are GONE. Granted the ORIGINAL observations could be used to generate pretty decent position estimates (depending on the original “order”), but I doubt that this would satisfy modern standards in very many cases.
The “problem” that I see is simply that this Treasure is disappearing at an alarming rate due to development, construction, AND vandalism. Dave Doyle mentions this quite often in his presentations, and I doubt that there is much that can be done about that (except maybe paragraph 2 above).
Furthermore, I just don't think that the NGS will ever see the kind of budget that a FULL-BLOWN readjustment of the “Classic” Network would require, so I seriously doubt that will ever happen again. We should be thrilled that they can do this NAD83(2011) Readjustment.
If every Surveyor tossed a fixed height Rod and an L1/L2 (or GNSS) receiver in the truck every time he/she went fishing, hunting, camping, or sightseeing, and made it a point to recover a station or two while the Dutch Oven was doing it's thing, that would go a long way. Some folks already do this to some degree or another.
I still have a T2, and maybe one of my LASER Geodimeters still works! If not, I might have to oil my 200 foot tape.
Loyal
But, Loyal, as you know, they did readjust the classical network in each state when they did the state-by-state HARN adjustments. So, it can be done. I would think that whatever they did back then (early-mid 90's) could be done again.
Even if a mark is now gone, it still may have conventional traverse or even GPS connected to it.
John
I suppose so...but my experience with the HPGN/HARN version of the Classic Passive Network has been somewhat less than encouraging. Mileage will of course vary a LOT. Out here in the West, the Classic Network isn't nearly as dense as it is Back East or even around the more developed areas of the West.
I have used the HPGN/HARN data to “reverse engineer” (guesstamate) Classic Stations relative to NEW GPS observations on the Extant Stations in the area...with reasonably good success, but it's pretty much hit or miss.
I agree that the NGS “could” (probably) do it, I just don't think that it's in the cards.
Loyal
John
Don't get me wrong here...
I would like to see everything brought up to date too.
BUT...given the cost-benefit ratio(s) involved, I would rather see whatever “discretionary” funds that are available to the NGS, spent on GRAV_D and the continuing research into, and development of, the Velocity Field Model (HTDP and TDP).
It boils down to dollars and sense.
Just my 2-bit opinion of course, nothing more.
Loyal
John
The readjustment using existing data would cost what, several office people for a few months? That is least-significant figures for GRAV-D.
Bill
Look at it this way, it appears that checking the existing (pre-2005) 2007 data set, and "coding" just the post 2005 GPS Projects into the Helmert Blocking scheme will take in excess of 6 months.
Besides which, I'm not sure that the NGS program used (NETSTAT I believe) supports "classical" observations to begin with (probably doesn't). My guess is that you would be looking at more like years than months. But I am wrong more often than I'm right these days.
Loyal
Classical obs
Not to mention the fact that there may not be as much experience with classical observations remaining at NGS as there once was. Maybe a contract opportunity for you John, or Mike P.
- Jesse
Classical obs
One thing I have been meaning to do when I get some free time (which looks like never) is to extract the observations from some Trans-Continental Traverse (TCT) loop from the NGS database, and adjust it as a standalone project, using just the 1960's era observations. Then, compare it against some high accuracy GPS positions.
For those who don't know anything about the TCT program, it was a survey to strengthen the conventional network to make it more accurate to support the space program. It was designed to be 1:1,000,000. But, I have never really seen any proof one way or another whether that accuracy was achieved. I have always been fascinated by this program. I have tied in a few of these stations over the years using GPS.
here is some good info about the program:
http://celebrating200years.noaa.gov/magazine/tct/welcome.html
Here is what it looked like at the end:
Classical obs
John,
Same here, I am really interested in that Zero Order Traverse, measured from towers, long lines, astro obs for position and azimuth, really cool stuff. I used a station that was part of that traverse located at Fort Hunter Liggett years ago. For anyone interested, the TCT is described in one of my favorite NGS publications starting on page 38 called North American Datum of 1983 - NOAA Professional Paper NOS 2 from 1989 with Charles Schwarz as the editor and many contributors like Bill Strange and others. It is called Super First Order on page 3 of the old Specifications to Support Classification, Standards of Accuracy, and General Specifications of Geodetic Control Surveys from 1982. I can't find a PDF of that, but here is a link to NOS 2 -
http://www.ngs.noaa.gov/PUBS_LIB/NADof1983.pdf
Excellent read folks.
Classical obs
I started messing around with some TCT data last night, and extracted the traverse from DC to the west side of Indiana.
Just one problem-I can easily get the directions, astro positions, azimuths, and distances. The distances are reduced mark-to-mark distances, which I am an advocate of (best way to store distances, in my opinion). But, the problem is that I am not able to get the vertical angle observations needed to use these distances in an adjustment. I have made an inquiry to NGS to see if I can get that critical bit of data for each line.
John
Where do you find that individual Station Data?
The Traverse (I believe) went right through this neck of the woods, and recovereing (OPUS_DB) a station or two might be a good project for Spud and I this summer (IF the snow ever melts).
Loyal