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And report which method you used to get those “horizontal” ground measurements if there is any possible misinterpretation.
I’m sure I know of a set of several surveys that report SPC distances with no note explaining that. Fortunately they are on flat land at a location where it only makes a difference of a couple tenths of a ft per mile. They don’t say what points were held for basis of bearings, either.
.And report which method you used to get those “horizontal” ground measurements if there is any possible misinterpretation.
I’m sure I know of a set of several surveys that report SPC distances with no note explaining that. Fortunately they are on flat land at a location where it only makes a difference of a couple tenths of a ft per mile. They don’t say what points were held for basis of bearings, either.
That would be a first for me, SPC distances but a different bearing basis.
no idea what you’re talking about with the theoretical definition stuff.
I believe this was Norm’s point in the post that started the thread. We all believe there is a mark-to-mark distance between two precisely marked points on a round earth and at different elevations, and it can be measured pretty accurately with GNSS, with distance computed from the XYZ coordinates.
But what is the horizontal ground distance between them? This is undefined a because the horizontal plane at one point misses the other point,.
It isn’t just an academic or philosophical matter, as shown by Moe’s practical example involving modest distances and significant elevation differences..
I see. I would just say this is simply the price you pay for using simple math. We could be using calculus and there most certainly is an equation for the curve between any 2 stations on the surface of the earth that would answer that question precisely, but surveyors chose not to go down that road so…
we’d still live in caves
Some portion of the world’s population still lives in caves.
And they routinely demonstrate how ineffective the world’s most advanced technology can be.
There are more ways to attain approximate ground values than I am capable of learning.
So why not accept the work that’s been done to design an approximate ground plane that works for everyone? Surveyor’s. Engineers. GISr’s, even dare I say architects and construction contractors. Everyone on the same sheet of music. I’ve seen it work on projects statewide with way more positive than negative comments.
@norm The long and short is, nothing will always work for everyone all the time.
Where a record LDP exists I nearly always use it. That covers about 15% of the places I work. Even the new datum and projections (if they arrive before I retire) won’t suffice for most of what I do. That’s not taking anything away from that work. It just means it doesn’t fit the needs of my client.
doesn’t fit the needs of my client
Interesting
That would be a first for me, SPC distances but a different bearing basis.
Oh, I think they are SPC bearings, but I don’t know which line he held when he did the fitting to get perfect closure on each of the several abutting and/or nearby plats, and there is enough span that they can’t all be pure SPC bearings and still close.
.Even the new datum and projections (if they arrive before I retire) won’t suffice for most of what I do. That’s not taking anything away from that work. It just means it doesn’t fit the needs of my client.
I would agree. Quite a few states appear to have bagged it on the “third layer” LDPs that could have minimized distortion way beyond the state zones, and dialed in their zone boundaries around administrative/political boundaries.
The state zones are an improvement over NAD83, to be sure, but I think an extra opportunity was squandered. Especially considering that we have another 2.5 years before the new datums drop. Plenty of time to fix it, but unlikely anything will be done.
Custom LDPs are awesome and will always have their place, but it would have been great to blanket the nation with standardized definitions.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanI planned to work on something for our LDP layer. Unfortunately I was reorganized back to the private sector before I had the chance. Doing it right was beyond a volunteer effort….
I know exactly what you mean. I moved down to WA around the time development of the new zones was really ramping up.
I was happy to donate my own time to the cause. I’d developed some rudimentary tools to automate the LDP development process, similar to the really slick ones that Michael Dennis and his team were using, and I was (still am) pretty excited about the new datums.
Unfortunately, it’s really, really hard to get ideas in front of the folks who make decisions at the state level, especially when those ideas promote change, improvement and progress.
I got discouraged pretty fast and dropped it.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanThe state zones are an improvement over NAD83, to be sure, but I think an extra opportunity was squandered. Especially considering that we have another 2.5 years before the new datums drop. Plenty of time to fix it, but unlikely anything will be done.
Please explain. I don’t understand. What needs fixed? Are you saying your state will only have 1 SPCS 2022 zone?
It was a consortium of state and county agencies, professional organizations and interested parties that brought it about plus an awesome design team. I was basically a listener and facilitator although I was technically involved in design decisions. As luck would have it our lead designer ended up leading the NGS effort for 2022. The new zones will have the same boundaries as the current but different parameters. Good grief – 8 years ago. Link
We will have one statewide zone (top layer), two state-level regional zones (middle layer), but no LDPs (bottom/third layer).
Weighting by population and switching to a single-parallel LCC is definitely going to help. And Washington State is definitely better off than most in that our population centers are close together.
Still, we could have created that third layer and dialed in those numbers even tighter. Not all work takes place in population centers, and being able to move between LDPs which are all around +/- 30ppm rather than SPCS at anywhere from -200 to 200 ppm (this is a low number, I’m just taking into account all the areas we are currently working) would be far preferable.
But maybe I’m in the minority.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postmanswitching to a single-parallel LCC
I read that the single parallel LCC are the average of the two parallels, so it doesn’t change anything.
I read that the single parallel LCC are the average of the two parallels, so it doesn’t change anything.
A single-parallel LCC is the average of two parallels…if you choose to make it the average. The simple average doesn’t work out correctly due to changing radius of the earth anyways.
The two-parallel model (at least as used mode widely) assumes scale parity at each parallel. But the single-parallel model lets the user pick the grid scale factor at that parallel.
So the single-parallel model can be tailored to suit depending how far above the ellipsoid the topographic surface lies.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanI’m a dummy. I was remembering one of the various iterations our state kicked around in the early stages of evaluation.
The southern half of lower Michigan is basically flat topography, and the final central latitude for the new Michigan South Zone didn’t move much from our original Michigan South Zone.
However, based on design criteria offered by the NGS, the central latitude would be at the center (average) of the two parallels at the topographic surface because the zone design dictates the total linear distortion (ppm), which is/should be equidistant from the central parallel. (i.e. no need to list both parallels.)
https://geodesy.noaa.gov/INFO/Policy/files/SPCS2022-Procedures.pdf
d. Linear distortion design criteria. Linear distortion is evaluated at the topographic surface for design, not the ellipsoid surface. NGS designs are based on both coverage area and population distribution (using data from the U.S. Census Bureau). Table 2 at the end of this section gives zone width and height ranges corresponding to various linear distortion ranges. i. The linear distortion design criterion is the smallest specific distortion range of ?ñ5, ?ñ10, ?ñ20, ?ñ30, ?ñ40, ?ñ50, ?ñ75, ?ñ100, ?ñ150, ?ñ200, ?ñ300, or ?ñ400 ppm that satisfies all three of the following minimum percentages: ?? 90% of zone population. ?? 75% of cities and towns (based on location only, irrespective of population). ?? 50% of total zone area.
When it will happen I don??t know but the signs are all around and technology is already in place. Sooner or later surveyors will have to gain the understanding of the 3d and 4d concepts for all task I believe. Because all others are already moving and moved that direction in architecture, construction, and in advanced engineering task. xYZ has been used in metrology for a while even though it is on a relative site like a manufacturer plant example. I had to take the xyz of mechanical engineers designs very great learning curve for my brain and then make that work with a known reference system wgs84. The system of systems. Now the kicker and hardest for me based on equipment was to get them on the flip side to understand was they designed something that fit itself but never truly understood that gravity still had power. Even a 4 foot carpenters level would defy the way it looked in a pure 3 d software. Now once they realized that the site items were going to be built by carpenters and machinist on the surface if the earth that does not have that same set of rules as the ground thaws or dries freezes and anything we attach to it or build on its inconsistent layer of soil grass water is forever changing and we can change it for a moment but she rules and changes as she wants to as well. It was fun mind boggling at times would have to say I learned a totally different set of skills and leaned how to use those skills i knew or I thought knew in ways that were not intended by the two different worlds of something being a plane and 3d and then reality. But good old redneck engineering and goode ole boy adaption and some folks way smarter than i and they were not always those with all academics but the team made up of all aspects of knowledge. Academia builders welders machinist engineers in variety of disciplines all working together to solve and figure out how to build make and measure and quantify all the results.
Sooner or later surveyors will have to gain the understanding of the 3d and 4d concepts
I once heard a licensed surveyor at a 3d training session say, “We’re land surveyors, we don’t give a _blank_ about elevations.” Continuing education is a requirement for a reason. Honestly, a person can learn quite a bit hanging around this forum. Some of it’s even useful.
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