The States will have ldp options, but the actual SPC zones will have too much distortion to be considered LDP.
NGS will have three layer options for each State. These will not happen on thier own and the process of development is well under way.
I'm heavily involved in the LDP being developed in the State of Texas. NGS isn't in favor of a three layer approach. Only two layers are generally acceptable: statewide and smaller zones. The smaller zones can be the current zones, smaller lower distortion zones designed by NGS, or true LDP designed by the states. The only three layer areas ideally acceptable are for cities on the edge of two zones.
The LDP zones designed by the States are absolutely true LDP (sub +/- 20ppm). Texas will go from 5 zones to approximately 53 zones.
Wow. I can't believe folks are bitching about?ÿ old SPC survey records as being problematic.?ÿ Yes, converting optical?ÿ ground observations to a contrived plane system is a distortion and can be woefully wrong concerning datum, mistaken calculations etc., but SPC's were designed to be good to 1 in 10,000 or so; in limited locale surveys the effect was trivial.?ÿ Personally I hated them because I'd do surveys?ÿ (10 mile locales) with major relief so the scaled distances were inappropriate .
The vibe I'm getting is some jackleg punches in an?ÿ GPS SPC coord from the 1970's record and finds he's 300' off and ignores the survey.?ÿ That's wrong,; the absolute coordinate is shrouded in history, but the relative positions are good to one in ten thousand in the local survey.
The suggestion that SPCS was intended to be no better than 1 in 10,000 is not an accurate statement. The original zones were designed such that the difference in ellipsoid and grid at any given point (ie grid factor) did not exceed 1 in 10,000. It's always been possible to apply the appropriate combined factors to account for the linear distortion.
I would say most of the distrust in published SPCs is a result of modern work and not work from the 1970s.
Shawn,
I was part of the original effort to establish LDPs in Oregon and am on the state committee working on the 2022 implementation. My understanding is the the NGS will be responsible for th first two layers and set the system up for the third layer. It is up to the individual states to establish, codify and populate the third layer. In Oregon we were able to remove the definitions of our coordinate systems for statutes and place them in administrative rules allowing an appointed committee of users to make the changes rather than legislators. Hopefully it will be any easy process to get our 40 LDPs in NGSs system.
fyi
355.6A(c). If the replacement of a monument at the preserved location is unsafe or impractical,
the surveyor may, in lieu of establishing a reference monument, use a federal, state, county,
or city geographic coordinate system to preserve the position
355.6A(c). If the replacement of a monument at the preserved location is unsafe or impractical,
This sounds like they don't want both a corner monument with ties AND coordinates, rather than encouraging their use.
Have you seen any Iowa corner records with coordinates?
I know someone fairly well who has.?ÿ
Thanks. First one I've seen with coords out of a few dozen I've looked at.
I looked up the record on line and indeed it is a well-known name. Interesting that he chose to use meters. No one will be confusticated by having their data collector set to the wrong kind of foot.
40 zones may seem like a lot until you realize that there are 36 counties in Oregon. Very nearly all of my projects in Oregon are in just one zone.
Good thing he did put coordinates on it.?ÿ As near as I can tell there was a fence on the 3/2015 Google Earth photo so the ties would help, but by 10/2015 I think the fence is gone and they are farming by "looks like about where it was plowed last year" with some wandering of the divide.?ÿ There might still be a corner post, but I'm not sure.
?ÿ
There is a reason for using meter even though few observe it or perhaps even realize it.
355.18 Identification of geographic locations.
The plane coordinate values for a point on the earth’s surface used to express the
geographic position or location of the point in the appropriate zone of the coordinate system
shall consist of two distances expressed in meters and decimals of a meter.
and that he lowered the stone well below the depth of a chisel plow. It could be that because he was in the field with the crew he realized the coordinate tie would far outlive the fence ties even though the fence ties only satisfied the law. Not to mention its a challenge to make swing ties through 170 feet of standing corn.
