Jim in AZ, post: 336313, member: 249 wrote: "...without the niceties of school or working for an LPS."
One or the other of those is a necessity, not a nicety.
For what its worth, he cannot obtain a license in VT without extensive work under a supervising LS.
Jim in AZ, post: 336313, member: 249 wrote: "...without the niceties of school or working for an LPS."
One or the other of those is a necessity, not a nicety.
As most other questions here are often answered: "It depends". 🙂
Certainly it would be for anyone who wishes to become an LPS. Often one, if not both, are a requirement depending on the state licensure rules. Even if one does not (I don't), it may not be the most efficient way to learn either. I get that, but my own circumstances preclude either.
I've found that the stuff you might learn in school (the theory) has been much easier to acquire than the practical--that you can only acquire in the field under the tutelage of someone (hopefully) with long and broad experience. Trial and error will get you so far, but it's the practical details in the field and in the office, that are almost impossible to learn without some form of apprenticeship.
One thing I do enjoy about Beerleg is that most questions garner a wide gamut of responses...something you're not likely to get from a single employer who's used to doing things ONE WAY, because that's the way HE learned to do it.
Add to that the wide range of surveying practice discussed here: From Williwaw's setting up tripods on hubs so they don't sink into the melting tundra (between running off grizzlys), to LeeGreen's dangling micro prisms on bridge beams taller than most men stand, to the host of guys here (from the midwest, west and south) from who's typical setups they can see 15 miles...it all adds up to a different kind of learning than one might get going to work for a single surveyor. (ps: I'd have to quit my day job to do so as well...then I couldn't afford the volume of field books I'm burning though).:-D
thebionicman, post: 336309, member: 8136 wrote: Using a DAF is simply applying the CAF to an existing projection. You are still using the scale and Elevation factor. They are incorporated into the parameters rather that being applied after. I've been using that method since the 90s..
Of course you are correct, I just want rfc to understand that I'm not looking at any numbers dealing with elevations or scale factors, I'm only making the grid and ground distances match, it's the only number I care about.
I'm not attempting to "get on" any particular elevation.
rfc, post: 336323, member: 8882 wrote: As most other questions here are often answered: "It depends". 🙂
Certainly it would be for anyone who wishes to become an LPS. Often one, if not both, are a requirement depending on the state licensure rules. Even if one does not (I don't), it may not be the most efficient way to learn either. I get that, but my own circumstances preclude either.
I've found that the stuff you might learn in school (the theory) has been much easier to acquire than the practical--that you can only acquire in the field under the tutelage of someone (hopefully) with long and broad experience. Trial and error will get you so far, but it's the practical details in the field and in the office, that are almost impossible to learn without some form of apprenticeship.
One thing I do enjoy about Beerleg is that most questions garner a wide gamut of responses...something you're not likely to get from a single employer who's used to doing things ONE WAY, because that's the way HE learned to do it.
Add to that the wide range of surveying practice discussed here: From Williwaw's setting up tripods on hubs so they don't sink into the melting tundra (between running off grizzlys), to LeeGreen's dangling micro prisms on bridge beams taller than most men stand, to the host of guys here (from the midwest, west and south) from who's typical setups they can see 15 miles...it all adds up to a different kind of learning than one might get going to work for a single surveyor. (ps: I'd have to quit my day job to do so as well...then I couldn't afford the volume of field books I'm burning though).:-D
I'm certainly glad that you are on this site - it is close to invaluable!
MightyMoe, post: 336305, member: 700 wrote:
You may think of it as raising the ellipsoid up to a new elevation, but that really isn't what you are doing, because state coordinates also have scale factors applied.
Is there a set elevation of each "State Plane"? Is it the mean elevation of the central meridian? The mean elevation of the ellipsoid wherever you are? It can't be the same in the Rockies as in Vermont, can it? I've been reading about how the entire system is devised, but it's like standing on the edge of a quicksand pool. There does not seem to be a way to just dip your toes in without getting sucked into a lot of spherical geometry.:-S
rfc, post: 336437, member: 8882 wrote: Is there a set elevation of each "State Plane"? Is it the mean elevation of the central meridian? The mean elevation of the ellipsoid wherever you are? It can't be the same in the Rockies as in Vermont, can it? I've been reading about how the entire system is devised, but it's like standing on the edge of a quicksand pool. There does not seem to be a way to just dip your toes in without getting sucked into a lot of spherical geometry.:-S
"0" is the set elevation. The "state plane" of course is a "plane", so it can't be at a constant 0 elevation. It is a slice through an arched surface. That arched surface, isn't at actual "0" either. geodetic "0" is not at a consistent ellipsoid. So the "plane" is slicing through a calculable figure. there is a "grid scale factor" to convert a distance from the plane to the ellipsoid and another to convert a distance from the ellipsoid to the ellipsoid height of the "ground" at the mean elevation between two points. In Colorado, all ellipsoid heights are 3500' or higher, so the factor is greater than a state that is close to sea level. Close to sea level using scale factors aren't really as significant than in a state @ a higher elevation.
rfc, post: 336437, member: 8882 wrote: Is there a set elevation of each "State Plane"?
There was an exception for NAD27 in Michigan where their state plane system was defined at 800 feet elevation as that was an average for the state. (they scaled the Clarke spheroid of 1866 by a factor of 1.0000382)
The NAD83 SPC are defined at zero on the ellipsoid surface everywhere AFAIK.
Elevation factors are also based on ellipsoid heights, NOT orthometric heights, I have seen some software get this wrong at least in the early days of GPS. For NAD27 it was assumed that the ellipsoid and ortho heights were the same surface (less computing power back then), so I think that may be why some software carried this practice forward.
SHG
rfc, post: 336437, member: 8882 wrote: Is there a set elevation of each "State Plane"? Is it the mean elevation of the central meridian? The mean elevation of the ellipsoid wherever you are? It can't be the same in the Rockies as in Vermont, can it? I've been reading about how the entire system is devised, but it's like standing on the edge of a quicksand pool. There does not seem to be a way to just dip your toes in without getting sucked into a lot of spherical geometry.:-S
Like Tom and Shelby say above NAD83 is ellipsoid based, to calculate the elevation factor use the ellipsoid number.
However the plane is not laying on the ellipsoid, it cuts through the earth like a flat paper cutting through a ball.
The Montana Coordinate System NAD83 eliminated the two zones that NAD27 state plane used, the plane cuts through the state and at latitude 45 and 49 it's set to 0ft. This means that the scale factor there is 1 and everywhere else it's less than 1 because the plane sinks below the ellipsoid for the rest of the state, except the SW corner. For some reason it was important that the scale factor didn't get larger than 1.:-S
rfc,
In order to really understand the geometry of State Plane Coordinate Systems (as well as UTM and LDP Coordinates), you have to ÛÏDE-weightÛ the mental image of a ÛÏPLANEÛ Surface.
The DEVELOPED SURFACE (actual geometric surface) of a SPC/UTM/LDP system (projection), is NOT [really] a PLANE, but a mathematically derived surface that ÛÏcan be laid out on a flat surfaceÛ (plane).
In the case of a Lambert SPCS, this DEVELOPED SURFACE is [a portion of] a CONE. In the case of a Transverse Mercator SPCS, the DEVELOPED SURFACE is [a portion of] a CYLINDER (or very nearly so due to the eccentricity of the underlying Ellipsoid).
That is not to say that there aren't many local ÛÏTangent PlaneÛ (or similar) coordinate systems lurking about, but NONE of the State Plane Coordinate Systems use a Tangent Plane projection.
If you haven't already done so, you should read Shawn Billings' article(s) in American Surveyor Magazine concerning Low Distortion Projections. There are (as I recall) some good illustrations, and certainly some good discussion of the basic geometry involved.
Loyal
Thanks Loyal, I keep misusing the term "plane". To me, it's a plane because we assign x.y coordinates which is a graphing for a plane, but I know I am technically wrong.
Here are links to Shawn's articles:
http://www.amerisurv.com/PDF/TheAmericanSurveyor_Billings-GroundVersusGrid-LDPpart1_Vol10No9.pdf
http://www.amerisurv.com/PDF/TheAmericanSurveyor_Billings-GroundVersusGrid-LDPpart2_Vol10No10.pdf
Tom,
I think that we ALL tend to think in those terms, and that's okay because we all know the underlying geometry. For someone like rfc who is just getting started, it is easy to misinterpret "our" use of somewhat generic terms common to surveying.
Loyal, post: 336523, member: 228 wrote: Here are links to Shawn's articles:
http://www.amerisurv.com/PDF/TheAmericanSurveyor_Billings-GroundVersusGrid-LDPpart1_Vol10No9.pdf
http://www.amerisurv.com/PDF/TheAmericanSurveyor_Billings-GroundVersusGrid-LDPpart2_Vol10No10.pdf
Tom,
I think that we ALL tend to think in those terms, and that's okay because we all know the underlying geometry. For someone like rfc who is just getting started, it is easy to misinterpret "our" use of somewhat generic terms common to surveying.
Loyal:
Thanks for that link! Excellent reading (and good sketches). Before I posted initially, I was looking for the thread started about 6 months ago (I think it was winter), with some pretty clear sketches of the geoid, ellipsoid, etc. and a lengthy discussion by several here significantly more savvy than me. I never could find it.
I'll continue studying it, but will not try to utilize any of it in practice for the time being. The immediate task at hand is to interpret the note on this recently done survey, and to utilize the bearings, at least for my own "basis of bearing". Here's the note:
Oops. Time ran out editing, lol....
Last fall, I attempted several Polaris shots, did the math, (applied the convergence, etc.), and came close to the bearings shown on the plat...but not so close (I think my best was out by somewhat more than 30") that I would "rely" on it for anything (other than a fond memory of freezing my butt off in early November in 15 degree windy weather waiting for Polaris to show itself).
But for my purposes here, precise azimuth shouldn't matter...This is completely local, not tied to anything else, and less than 2000' end to end, and less than a few hundred feet in elevation, and using only a total station. As for distances, they probably are ground, and now that I've learned how to pay fastidious attention to HI's and HR's, I might be able to replicate some of them doing closed, point to point traverses (I think it's called a "compound" traverse).
By the way, is Shawn related to these Billings, here in my neighborhood?:
http://www.nps.gov/mabi/index.htm