There are a number of issues with DPPS some known and some unknown.
Kent McMillan, post: 405730, member: 3 wrote: Mostly, the main ones are known, though. They are:
- delivery of coordinates in same system as those given upon the plat,
- accomodation to new datum,
- effect of long-term crustal movements,
- future advances in positioning technology,
- ability of surveyors to use coordinate-based cadastral data properly,
- ability of non-surveyors interested in cadastral information to use coordinate-based cadastral data properly,
- problems arising from incorrectly located boundary corners from mistakes attributable to coordinated cadastre,
- legal status of monuments placed to represent the positions upon the ground of coordinate-based corners.
"- delivery of coordinates in same system as those given upon the plat." This shouldn't be an issue, unfortunately it currently is with some (too large) percentage of practicing surveyors. This will become a negligible problem as software improves and surveyors become better educated. Currently it's a problem.
"- accomodation to new datum," This also shouldn't be an issue as long as NGS is adequately funded.
"- effect of long-term crustal movements," This is a problem as well as short term seismic events. Dr. Jeff Freymueller of the UAF Geophysical institute notes "To maintain an error tolerance in coordinates of 5 cm (2 inches) for a spot on the ground over 50 years, you need to know the rate of change
of the coordinates with an accuracy of 1 mm/yr. Neglecting a movement rate of 1 centimeter per year results in an error of about 1.5 feet in 50 years. A large earthquake could cause a similar change in coordinates, even if the fault is miles away. At this level of coordinate accuracy, we even have to deal with the cumulative displacements from potentially distant earthquakes (in the 2002 Denali fault earthquake, Fairbanks moved about 6 cm south and Anchorage about 2 cm west). Closer to large earthquakes, the displacements can be much larger ÛÒ as large as several feet or tens of feet, and these large earthquakes are always followed by transient, non-linear deformation (also potentially as large as several feet over many years) that currently must be observed because it cannot yet be predicted accurately."
You st
"- future advances in positioning technology," This will only help
"- ability of surveyors to use coordinate-based cadastral data properly," Hopefully that issue is minimized over time
"- problems arising from incorrectly located boundary corners from mistakes attributable to coordinated cadastre," I'm not sure what you are alluding to here - transposed coordinates by the establishing surveyor? or??
That reminds me - you had asked or stated about bearings and distances on the DPPS plat in an earlier post - there are NO bearings or distances on the DPPS plat between new section corners - there are a few record or measured values on the perimeter. And THERE are NO ties to adjacent surveys - the ties between the new section corners and the adjoining cadastral corners are unreported
"- legal status of monuments placed to represent the positions upon the ground of coordinate-based corners." This is a fairly big one - it will take statutes/regulations and a body of law to resolve disputes/ambiguities under DPPS. This will consume time and money.
You also stated "I read the letter, but the main substance of it was that NGS didn't have good models of crustal movement in Alaska. The obvious fix for that is to install an array of permanent reference marks across the area to be subdivided and conveyed by patent and in locations that promote their use and periodic reoccupation to detect crustal movement. I would think that Alaska could take over the periodic (meaning: every five or ten years or upon new datum) resurveying of the network of reference marks and distribution of new values." That is an obvious fix without funding or legal infrastructure to implement. There is interest in doing this by Dr. Jeff Freymueller - BLM should get a cost to do this and fund it into the next century since they are proposing a system that relies on it.
BLM should also establish a fund for handling all of the issues spawned by the implementation of DPPS. It can be an escrow account - if DPPS doesn't consume it in 50 years - BLM can have it back - on the other hand if it looks like it's getting depleted - BLM can fortify the fund to cover the cost. BLM hasn't expected any other state to foot the bill for their experimentation.
As an aside - It's really hard to know if unknowns are main issues since they are unknown.
Kent McMillan, post: 405737, member: 3 wrote: Yes, I read that bit and thought it was a false choice. What they are describing was having to go find some boundary monuments on the remote EXTERIOR of the entire tract, whereas the much more efficient solution would just be to tie to closer reference points with positions in the same coordinate system as that in which the boundary corners are published. Much different thing.
From that section "These control monuments and other accepted Three Plus Method monuments could be the basis for corner monumentation densification."
Of course the first monuments set have to be based on the limited monumentation that is shown on the Group 948 plat. The report is saying that after that mon densification comes from the use of other state accepted monuments (all of them having a pedigree that goes back to the original Group 948 plat or other basis that is acceptable to the state).
That's not going to some boundary monuments on the remote EXTERIOR of the entire tract.
So KentÛ? There is no doubt that with enough infrastructure development and education and legal support and money, DPPS can be cobbled together ÛÒ itÛªs a new system and it itÛªs nowhere turnkey. It certainly isnÛªt what BLM is marketing it to be (attached). Why, when all of the other PLSS states received the monumentation that was agreed upon (and some of that monumentation was in VERY remote land at the time it was planted), should ONE state be burdened with the cost and effort to be the proving ground for something as questionable as DPPS?
As this group knows better than any group: ItÛªs much much more expensive to fix problem boundaries than it is to establish them properly to start with.
JKinAK, post: 405745, member: 7219 wrote: There are a number of issues with DPPS some known and some unknown.
"- delivery of coordinates in same system as those given upon the plat." This shouldn't be an issue, unfortunately it currently is with some (too large) percentage of practicing surveyors. This will become a negligible problem as software improves and surveyors become better educated. Currently it's a problem.
By "delivery", I had in mind the technology by which accurate coordinates in the same system as the plat of record were determined on the ground as needed. One objection was that relying upon OPUS solutions would be too expensive since it would necessarily involve at least two trips to some areas: one to establish control points for post-processing and one to mark the positions of corner coordinates in relation to control.
The future holds other options, I'm certain.
JKinAK, post: 405745, member: 7219 wrote: "- accomodation to new datum," This also shouldn't be an issue as long as NGS is adequately funded.
So, how certain are we that the Rand McNally Corporation or whichever company bought National Geographic won't be in charge of developing some new, proprietary datum in the currently crazy environment?
JKinAK, post: 405745, member: 7219 wrote: "- effect of long-term crustal movements," This is a problem as well as short term seismic events. ...
This is really just an argument in favor of establishing reference monuments in places that are accessible, stable, and suitable for GPS operations. Periodic resurveys of those monuments will serve to detect crustal movements and provide a basis for recomputation of the record coordinates at some newer epoch.
KinAK, post: 405745, member: 7219 wrote: "legal status of monuments placed to represent the positions upon the ground of coordinate-based corners." This is a fairly big one - it will take statutes/regulations and a body of law to resolve disputes/ambiguities under DPPS. This will consume time and money.
I don't see it as that difficult to turn into an Alaska statute that applies only the to lands patented in DPPS townships. It all boils down to what evidentiary weight should be assigned to markers that are in place at approximately the correct position. That isn't a particularly new problem in itself, but the law could specify acceptable limits.
JKinAK, post: 405749, member: 7219 wrote: Of course the first monuments set have to be based on the limited monumentation that is shown on the Group 948 plat.
No, actually my point was that the official plat should also show the reference monuments within the township, also with coordinates in a useful system. I'd suggest ECEF coordinates as well as LLH. In other words, the convenient reference monuments would be legal evidence of the subdivision upon which the patents issued.
Kent McMillan, post: 405753, member: 3 wrote: No, actually my point was that the official plat should also show the reference monuments within the township, also with coordinates in a useful system. I'd suggest ECEF coordinates as well as LLH. In other words, the convenient reference monuments would be legal evidence of the subdivision upon which the patents issued.
The Group 948 plat does show all of the tied monuments (49) within the 37 townships that the plat covers. If there were other reference monuments, BLM has chosen not to tie them or display them on the plat. I'm OK with them just showing NAD83(2011)(Epoch 2010.0000) coordinates - I don't see a benefit to showing ECEF coordinates and there's the potential that they'll introduce unanticipated issues in the future. Sometimes less is more.
JKinAK, post: 405756, member: 7219 wrote: The Group 948 plat does show all of the tied monuments (49) within the 37 townships that the plat covers. If there were other reference monuments, BLM has chosen not to tie them or display them on the plat. I'm OK with them just showing NAD83(2011)(Epoch 2010.0000) coordinates - I don't see a benefit to showing ECEF coordinates and there's the potential that they'll introduce unanticipated issues in the future. Sometimes less is more.
The thing is that if you are comparing ECEF coordinates in one datum to ECEF coordinates in either another or the same datum at another epoch, the transformation should be more direct. It also guarantees that the vertical componenent of the coordinates will be supplied, too.
If you give the ellipsoid heights of the reference monuments, though, as well as the Latitudes and Longitudes,, that will be sufficient to compute the ECEF coordinates.
Is the Group 948 plat available on line for a look?
I'm not sure if it's online. I've got the version that was handed out at the BLM workshop - it's too large to upload even in thirds. I don't have time know but I'll break it into smaller chunks and upload it later.
Group 948 Draft 20150319 Pages 1-10 of 42
Group 948 Draft 20150319 Pages 11-20 of 42
Group 948 Draft 20150319 Pages 21-30 of 42
Group 948 Draft 20150319 Pages 31-42 of 42
That's it. The final has some minor changes but nothing that changes the character or intent. Some things that are different from a typical USRS - very few bearings and distances - absence of meanders - section corners in water bodies (not that it matters - just different) - notice the absence of ties to adjacent surveys. It's hard to grasp the scale - there are some pretty large gaps between many of the control points such as C1-D1 14 miles. It's a lot of land without many monuments.
This isn't a modern innovative way to survey - it's simply a cost shift.
JKinAK, post: 405776, member: 7219 wrote: It's a lot of land without many monuments. This isn't a modern innovative way to survey - it's simply a cost shift.
I'll grant you that that these plats are woefully short on control monuments from which the coordinate system may be readily established on the ground. It is not too much to ask to expect that there be at least three or four per township and in spots that are suitable for GPS occupation/ They should also be as stable and accessible as possible, unless stable is simply not feasible. In that case, it does make sense not to spend loads of time placing monuments that won't be even within a decimeter of the same position two or five years from now.
The idea is very good, but not yet fully thought through.
I have no comment on the merits of this plan, but I would like to point out that when the land is patented by the state and the private owner hires a surveyor the surveyor will not only have to get to the land owners property, they will also have to travel up to 12 miles to a control monument. There are no roads or even trails, so every survey will require a helicopter or a multi night backpacking trip.
The cost will be so cost prohibitive it won't be done. Everyone will rely on their handhelds.
Kent McMillan, post: 405698, member: 3 wrote: Is this what the federal statute provides as to necessary surveys?
This is US code, not statute, and it does not apply to land selected by the state.
aliquot, post: 405800, member: 2486 wrote: This is US code, not statute, and it does not apply to land selected by the state.
I dunno. It looks to me like the Alaska Native Claims Settlement Act (ANCSA) which became Public Law 92-203 (85 Stat. 688)
https://www.gpo.gov/fdsys/pkg/STATUTE-85/pdf/STATUTE-85-Pg688.pdf
aliquot, post: 405799, member: 2486 wrote: I have no comment on the merits of this plan, but I would like to point out that when the land is patented by the state and the private owner hires a surveyor the surveyor will not only have to get to the land owners property, they will also have to travel up to 12 miles to a control monument. There are no roads or even trails, so every survey will require a helicopter or a multi night backpacking trip.
So, what is the value of land that is that inaccessible? Is it even $50.00/acre? I'm assuming that the cost of surveying in those remote locations is so high that even the supposedly "inexpensive" option would cost between 30% to 50% of the value of the land.
As for using handheld receivers to navigate to corners and flag lines: at what threshold does the available accuracy of a handheld receiver become more than adequate for the feasible land uses? +/-1.5m? +/-0.3m? +/-0.1m?
Kent McMillan, post: 405802, member: 3 wrote: I dunno. It looks to me like the Alaska Native Claims Settlement Act (ANCSA) which became Public Law 92-203 (85 Stat. 688)
https://www.gpo.gov/fdsys/pkg/STATUTE-85/pdf/STATUTE-85-Pg688.pdf
But that is for native claims. It does not apply to state selected land.
Kent McMillan, post: 405805, member: 3 wrote: So, what is the value of land that is that inaccessible? Is it even $50.00/acre? I'm assuming that the cost of surveying in those remote locations is so high that even the supposedly "inexpensive" option would cost between 30% to 50% of the value of the land.
As for using handheld receivers to navigate to corners and flag lines: at what threshold does the available accuracy of a handheld receiver become more than adequate for the feasible land uses? +/-1.5m? +/-0.3m? +/-0.1m?
I am fairly confident that there is no privately owned land in Alaska worth anywhere close to $50/ acre. A very large tract with no landing strip might get as low as $600-700 an acre.
But you are right, and that was my point, if the state does not use tax dollars to survey these lands they will probably never be surveyed by a land surveyor.
aliquot, post: 405809, member: 2486 wrote: I am fairly confident that there is no privately owned land in Alaska worth anywhere close to $50/ acre. A very large tract with no landing strip might get as low as $600-700 an acre.
So, the State of Alaska is going to sell the lands that the United States patents to it for more than $650/per acre, but doesn't want to spend any money actually surveying the land? Similarly, someone who has more than $100k to spend on some remote 1/4 section of recreational land that is only accessible by helicopter will be bankrupted if a surveyor takes two trips to survey it?
aliquot, post: 405809, member: 2486 wrote: But you are right, and that was my point, if the state does not use tax dollars to survey these lands they will probably never be surveyed by a land surveyor.
Well, if the land will never need to be surveyed by a land surveyor and handheld accuracies are more than adequate for recreational uses, why is this a problem if the whole deal isn't just a make-work scheme for land surveyors?
Given the high mobilization costs in remote parts of Alaska, why wouldn't a surveyor use a commercial satellite-based differential correction service to mark lines and corners on a tract with specified coordinates. I'd think that decimeter accuracies wouldn't be impossible for fairly modest subscription costs. Is decimeter accuracy really not plenty good for such work?