@rover83?ÿ
A co-ordinate cadastre works well on a stable land mass but here in NZ (and elsewhere in world) we are are on the border of two tectonic plates that are moving in the order of 50mm ( https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/geodetic-datums/new-zealand-geodetic-datum-2000-nzgd2000/nzgd2000-deformation-model) different to each other.
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While the deformation model can model the standard movements, earthquakes are not so predictable (both solid plate movement and localised liquefaction) nor are local landslip events or mining induced effects. In these cases monuments and occupation on boundaries become very important. No model covers every situation perfectly, it's just is it good enough for your application.
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For it to work here we would need a very dense network of CORS to model all the local variances to standard plate movement.
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If it could be done would simplify boundary surveying to be just like construction where if you do your job right the result will be correct. With boundary here you can do all your measurements perfectly and still have problems to resolve when the underlying monuments don't match the record.
With boundary here you can do all your measurements perfectly and still have problems to resolve when the underlying monuments don't match the record.
Testify brother!
@lukenz?ÿ
Local movement is going to be an issue whether we're working with coordinates or monuments. It's certainly something to take into account, but it's not everywhere, nor is it insurmountable. I've worked on West Coast USA projects from Alaska down to California, and the NGS Horizontal Time-Dependent Positioning tool has proven reliable and repeatable. It does get updated regularly to account for local movement as data are gathered and movements modelled.
Horizontal movement is not as localized as vertical movement at least, so for cadastral work the difficulties are lessened. Around here, reference stations are clustered around the fastest-moving areas of the country.
If we're talking natural disaster, with a large swath of monuments being wiped off the earth at once, I'd say having coordinates in a well-developed reference frame with modelled velocities and incorporating local movement would be a massive help for reconstructing and remonumenting parcels.
Just like bearings & distances, geodetic coordinates are another piece of information in the jigsaw puzzle of boundaries that may become relevant when physical monuments are unavailable. Whether we use bearings & distances, proportioning, or some other method to compute a point to set, we're still setting a monument at a coordinate that we have computed.
OK you have coords on a property corner or 4 corners. The earth moves a foot. You do a survey. Where are the corners? At the original coords? Do the corners move with the land? You had a zero offset building on the lot line. Is it now 1 foot over the line or did the line move with the land? When only half of the property moved are the coords valid positions for 2 corners but not the other 2. How would this work?
@lurker?ÿ
the coordinates by the nature of how they created, wouldnt move, even if the earth does....?ÿ Say for the ECEF model, even if the corners of the lot spun and by some weird coincidence there was one corner that maintained position, and the other three rotated out of the original position, their coordinates would change, as would their position. its the whole idea of coordinates that is beguiling, they seem to be an easy fix to a complex mathematical modeling. throw gravity into the mix and boy howdy then we got tidal changes and woohoo where is the ECEF really at, at that moment in the space time continuum....throw in a big earthquake and now youre really screwed, slowing the orbital procession and everything else. fun times.
@dougie I don't see why land surveyors or architects who draft by hand should be a barrier to submitting officially required drawings in electronic form. An example of this is the Vermont Land Survey Library. The survey is submitted in PDF format. I'm not a surveyor, but I don't see anything that requires the surveyor to include state plane coordinates or latitude & longitude on the drawing. So the surveyor who likes to draft by hand just goes down to Staples and has them scan the drawing.
How many posts have been made in this forum where surveyors say the CAD files never leave their office? Whenever another design professional wants an electronic version of a survey, they get a PDF with all the good stuff stripped out. How is that any different than scanning a mylar drawing?
I'm not saying this is a good thing. I'm a notary, although I seldom use the qualification. Our state recently passed a uniform law on land records that allows any notary to take an electronically signed land document (example: deed) with an electronic notarization, print it, and certify it as a true copy. Then it can be recorded in the land records; very handy for towns that are not equipped to accept electronic land records (example: every town and city in Vermont). The down side is that all the security measures incorporated in the electronic signatures just went into the bit bucket.
I've always kind of wondered that too.?ÿ If I remember right, from one of the textbooks in school there was a line about land ownership describing 'a cone from the middle of the earth extending into the heavens above'.?ÿ I took that to mean the cone never moves even though the land itself might.?ÿ It wouldn't surprise me if my interpretation was wrong though.
One of big reasons for the move to the modernized NSRS is the fact that the earth moves. The NGS will be tracking both plate movement through Euler Pole Parameters, and local movement through the Intra-Frame Deformation Model, both of which are integral to NATRF2022.
At this point, while coordinates are not a cure-all by any stretch, the ability to track plate and local movement is pretty darn good and continues to improve. The vast majority of CONUS can be tracked and modelled by the EPP; in those areas NATRF2022 coordinates will actually not change over time - although the NGS will periodically be publishing Reference Epoch Coordinates. In areas of local movement the IFDM will be applied. The blueprint documents for NATRF2022 do a better job of explaining it than me.
It sounds like there's a lot of concern that as soon as we have coordinates on a point, all surveyors are somehow going to flip a switch and ignore all other forms of evidence. I don't see that happening. We've stood with one foot in the past and one in the future for a long time, as @williwaw said upthread. We can continue to do so.
https://www.cnn.com/2022/08/12/weather/california-megaflood-study/index.html
This article really caught my attention given the pervasive drought in the west. Pendulum always swings both ways. I'm sure a good many California surveyors are more familiar with the problems associated with subsidence in the Central Valley from over drawing ground water. Throw in an atmospheric river fire hose.... They state the recovery costs could be 5x Katrina and they are over due for another event like 1861-1862, but likely worse with warmer temperatures holding more water vapor. I'd think after such an event, a backhoe would become standard equipment looking for corners.
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