To expand on Shawn's post a wee bit.
Not to put too fine a point on it, but the Projection Parameters (constants) defining the various State Plane Coordinate System Zones (ÛÏthe gridÛ DWoolley described), don't factor in gravity OR elevations (as Shawn pointed out). Granted, the underlying geodesy used to generate Ellipsoid definitions (like WGS84 or GRS-80), factor in things like gravity, but the State Plane System is pretty much a 2-dimensional ÛÏfitÛ to a 3-dimensional problem. All you need to compute an SPC or UTM Coordinate, is a Latitude & Longitude expressed in the SAME Datum (e.g. NAD27 or NAD83) as the SPC Zone that you want to play in. Use the wrong Datum (or realization of NAD83) and you get into spatial trouble. Elevation (Ellipsoid Height for NAD83) doesn't factor into the computation, UNTIL IT DOES...
Elevation (Height/Topography) enters into this discussion when one attempts to actually apply SPC (or UTM) coordinates to the real world (you know, the real world where the rubber meets the road, NOT some theoretical developed surface that might be a MILE [or 2 or 3] below you). For folks who live by the coast, or in relatively low lying areas, this isn't [usually] much of a problem, because the Developed Surface (grid) is pretty close to the topographic surface (GROUND).
So... folks along the coast, and to some extent in inland areas with little relief or elevation, tend to buy into the old ÛÏSPC = 1:10,000Û myth, however, that ratio falls apart FAST in most parts of the country.
Since starting surveying in 1968, I have worked [somewhat briefly] at ÛÏsea level,Û as well as over 10,000 ft. If I were to sit down and figure out the ÛÏaverage ElevationÛ on the ÛÏaverage field dayÛ over the last 48 years, it would be somewhere between 6000 and 8000 feet (hell, my front porch is at 7100 feet). With VERY few exceptions, my work has been directly related to either the PLSS or US Mineral Surveys, and BOTH of these are based on ÛÏTrue BearingsÛ and Distances measured on the SURFACE of the Earth. All of the Lands (properties) in my neck of the woods, are BASED (at least originally) on either the PLSS or US Mineral Surveys (oh there are a few exceptions, but not many).
Okay, so where I live in Southwestern Wyoming, so I fall in Wyoming West Zone (4904), which is a Transverse Mercator Projection defined as follows:
Datum NAD83
Central Meridian 110å¡05' West
Origin Latitude 40å¡30' North
Scale Reduction 0.999 937 500 (1:16,000)
False Northing 100,000 meters
False Easting 800,000 meters
You may notice that the Wyoming Zones are significantly ÛÏsmallerÛ (less scale distortion) than most SPC Zones (1:16,000 v. 1:10,000). BUT the 1:16,000 is only relative to the surface of the NAD83 Ellipsoid (which we ain't got any of in Wyoming). Because the Wyoming Zones are ÛÏsmaller,Û their developed surface never gets above about 1200 feet, yet the average elevation in Wyoming is 6,700 feet...go figure! On the flip side, they never get any ÛÏdeeperÛ than 1200 ft. either.
Here is a [truncated] copy of the NGS Data Sheet for our local FBN Station a couple of miles from me:
MR0820 PID - MR0820
MR0820 STATE/COUNTY- WY/UINTA
MR0820 COUNTRY - US
MR0820 USGS QUAD - EVANSTON (1978)
MR0820
MR0820 *CURRENT SURVEY CONTROL
MR0820 ______________________________________________________________________
MR0820* NAD 83(2011) POSITION- 41 15 17.06617(N) 110 58 53.36028(W) ADJUSTED
MR0820* NAD 83(2011) ELLIP HT- 2126.629 (meters) (06/27/12) ADJUSTED
MR0820* NAD 83(2011) EPOCH - 2010.00
MR0820* NAVD 88 ORTHO HEIGHT - 2141.6 (meters) 7026. (feet) GPS OBS
MR0820 ______________________________________________________________________
MR0820 NAVD 88 orthometric height was determined with geoid model GEOID99
MR0820 GEOID HEIGHT - -14.906 (meters) GEOID99
MR0820 GEOID HEIGHT - -15.170 (meters) GEOID12B
MR0820 NAD 83(2011) X - -1,720,000.922 (meters) COMP
MR0820 NAD 83(2011) Y - -4,485,086.154 (meters) COMP
MR0820 NAD 83(2011) Z - 4,185,135.348 (meters) COMP
MR0820 LAPLACE CORR - 6.73 (seconds) DEFLEC12B
MR0820
MR0820; North East Units Scale Factor Converg.
MR0820;SPC UT N - 1,102,451.767 543,454.494 MT 0.99995684 +0 20 30.8
MR0820;SPC UT N - 3,616,960.51 1,782,983.62 sFT 0.99995684 +0 20 30.8
MR0820;SPC WY W - 184,198.911 724,729.496 MT 1.00000720 -0 35 32.2
MR0820;SPC WY W - 604,325.93 2,377,716.69 sFT 1.00000720 -0 35 32.2
MR0820;UTM 12 - 4,567,036.478 501,550.797 MT 0.99960003 +0 00 43.9
MR0820
MR0820! - Elev Factor x Scale Factor = Combined Factor
MR0820!SPC UT N - 0.99966654 x 0.99995684 = 0.99962339
MR0820!SPC WY W - 0.99966654 x 1.00000720 = 0.99967374
MR0820!UTM 12 - 0.99966654 x 0.99960003 = 0.99926670Look at the combined factors! For Wyoming West SPC, we are NOT seeing 1:16,000 or even 1:10,000... but 1:3,064. That's .33 feet in 1,000 feet, 0.86 feet in half a mile.
Now Main Street in Evanston sits at about 6755 NAVD88, and homes within the City Limits range from about 6600 to about 7200 feet. So our postage stamp sized little burg (~10 sq. Miles) has more topographic relief than the entire state of Florida, or Delaware, or Louisiana.
Our TINY (relative to other Wyoming counties) 2000 sq. mile County has elevations ranging from about 6290 to just above 9760, which means that there is more topographic relief in Uinta County, than the states of Alabama, Arkansas, Connecticut, Delaware, Florida, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Michigan, Mississippi, Missouri, New Jersey, North Dakota, Ohio, Pennsylvania, Rhode Island, Wisconsin, or the District of Columbia.
Okay; so two points where the Developed Surface (grid surface) of the Wyoming West Zone gets ÛÏclosestÛ to the topographic surface in Uinta County, are:
Intersection of the Bear River and the Utah State Line @ ~6340 NGVD29:
41å¡31'17.8Û N = 213,894.3 m North
111å¡02'44.9Û W = 719,668.5 m East
k = 1.000 017
q = -0å¡38'17Û (angle Grid to Geodetic [CW])Putting the rubber on the road:
6340(29) = 6344(88) -49.5(N) = 6294(NAD83 EH = 1918.4 meters)
Vc = 1.000 301 (Vertical coefficient Ellipsoid to Ground)
gG = 1.000 284 (grid to Ground) more or less = 5,937 feet ABOVE the ÛÏgridÛ
1:3521And the Northeast Corner of the County, which is pretty much the bottom of Porter Creek just before it meets the Blacks Fork @ ~6290 NGVD29:
41å¡34'38.8Û N = 219,648.4 m North
110å¡02'52.9Û W = 802,944.2 m East
k = 0.999 938
q = 0å¡01'24Û (angle Grid to Geodetic [CCW])Putting the rubber on the road:
6290(29) = 6294(88) -49.2(N) = 6244.8(NAD83 EH = 1903.4 meters)
Vc = 1.000 299 (Vertical coefficient Ellipsoid to Ground)
gG = 1.000 361 (grid to Ground) more or less = 7,547 feet ABOVE the ÛÏgridÛ
1:2770Of course it gets [much] worse at the ÛÏhigh pointÛ of the county:
Ridge between Willow Creek & Archie Creek on Utah State Line @ ~9760:
40å¡59'46Û N = 155,184.7 m North
110å¡31'43Û W = 762,536.6 m East
k = 0.999 955 (projection Scale Factor)
q = -0å¡17'32Û (angle Grid to Geodetic [CW])Putting the rubber on the road:
9760(29) = 9765.3(88) ÛÒ 42.33(N) = 9723.0(NAD83 EH = 2963.6 meters)
Vc = 1.000 465 (Vertical coefficient Ellipsoid to Ground)
gG = 1.000 510 (grid to Ground) more or less = 10,662 feet ABOVE the ÛÏgridÛ
1:1961Another thing to think about:
Just down the Freeway a bit, is Salt Lake County (in Utah), which covers only ~800 sq. miles, but has ~7,120 feet of relief. Only 14 STATES (including Utah obviously) have more relief. And there are other counties in the West that exceed that topographic range.
The developed surface of the Utah State Plane systems (Zones) range from about 2000 feet BELOW the NAD83 Ellipsoid, to about 2000 feet ABOVE the NAD83 Ellipsoid. I believe that the actual extremes are something like ~2,116 Below along the central parallel of the Central Zone, and ~2,807 above at the corner of Box Elder, Davis, Tooele, and Weber Counties (Also Central Zone), out in the Great Salt Lake.
The LOWEST point in Utah has an elevation of ~2,180 feet, and the highest point is about 13,518 feet, and the average Elevation is about 6,100 feet.
Convergency Angles range from about -1å¡40'30Û @ the Corner of Utah/Idaho/Nevada, to about 1å¡36'56Û @ the Corner of Utah/Colorado/Wyoming. The Southwest and Southeast Corners of the state are similar (only slightly less).
If you want a real good laugh, take a look at Montana NAD83 SPCs, the Wyoming Statewide Lambert, or the Texas Statewide Shackelford Projections. All of these HUGE ÛÏgridÛ Zones have their place, and so do UTM Zones, BUT... IMO, they are not the best way to RETRACE, Resurvey, or describe properties that have their origin in ÛÏTrue North & Ground Distances.Û These humongous grid systems make perfect sense to me, I GET IT! Utah and Nevada, use UTM Zones for the same reason/purpose. When you have to spatially relate everything within an entire state into a singular spatial database, that's the easiest way to it. No harm no foul.
SURE, you can input all of the ÛÏTrue Bearing/Ground DistanceÛ data into AutoCad, then scale and rotate it into some sort of SPC[ish], UTM[ish], coordinates before going to the field. BUT when you are done, do you report/return SPC Grid Bearings and Grid Distances on your Plat? I suppose you could, and if you state that is what you did, I won't have any problem figuring it out. But when your ÛÏrecordÛ and ÛÏmeasuredÛ are APPLES and ORANGES, it kinda makes folks wonder if you really know what you are doing.
Just my Opinion (and the PLSS ÛÏdatumÛ looks better everyday for Cadastral Work...except in Texas, where the Shackelford is probably okay)
P.S. So I guess; Size does matter!
:whistle:
Loyal
Yes, I'm working on a project a couple of miles in extent right now where the Combined Scale Factor varies by as much as 2ppm from the average for the project. In other words, a Horizontal Surface Distance computed using the average Combined Scale Factor will be in error by as much as 2ppm, or 0.01 ft. per mile. I'm tremendously glad that you've identified this HUGE problem with the Texas Coordinate System of 1983.
Kent McMillan, post: 375683, member: 3 wrote: Yes, I'm working on a project a couple of miles in extent right now where the Combined Scale Factor varies by as much as 2ppm from the average for the project. In other words, a Horizontal Surface Distance computed using the average Combined Scale Factor will be in error by as much as 2ppm, or 0.01 ft. per mile. I'm tremendously glad that you've identified this HUGE problem with the Texas Coordinate System of 1983.
Yep...working in pancake land makes it a lot easier. Of course the Shackelford would work just as well!
Loyal
Kent,
Here are the NAD83 Shackelford Projection constants in case you lost them:
Shackelford
Lambert Conformal Conic
GRS-80
NAD83
Longitude of Origin 100å¡ West
Latitude of Origin 31å¡10' North
North Standard Parallel 34å¡55' North
South Standard Parallel 27å¡25' North
False Northing 1,000,000 meters
False Easting 1,000,000 meters
I'll bet it works just as well on your LITTLE project.
Get back to us with the comparison buddy.
Loyal
So many issues with SPC, I'm not sure if just living at elevation and also using the 83 mess that is montana makes it easier for surveyors to understand in this area, but we sure don't have the confusion I hear about from other parts of the country.
I do have a project that the vendor wants in state plane bearings and ground distances. Another survey company did the first set of drawings and now we are doing them after they retired from the business.
The surveyor who started it came up with an elegant solution to handle the issue, at each township line as he headed north he has a new scale factor, because of the distortions he begins about .99985 and ends up about .99945 or 400ppm across the site, the .99945 combined factor is actually lower than the .99985
Anyway, using his plan has worked well so far, I can surely see why he did it.
Heck, I have one contractor that does many of the areas large buildings, if he sees more than a 1/4" he's calling, imagine if I tell him he has to adjust his measurements 1/2" per 100' because it's just too much for me to use surface distances with my equipment (most control here is modified SPC).
The 1 part in 10000 feet is a scale of .9999,,,,,,,,,,,I've never seen that in state plane, nothing close except the very south border of Mont.
U. S. Coast and Geodetic Survey
DIVISION OF GEODESY
-- = _. ". - = - - :: =- = = = = = = = = ~ = = : = = = = = = =
USGS GEODETIC LETTER
Volume 4 January, 1937 Number 1
Extensive use is being made of the coordinates in North Carolina,
South Carolina, Georgia, Florida, Alabama, Tennessee, Louisiana,
New Jersey, Connecticut, Massachusetts, Iowa and many other
States. An accurate map of Denver and vicinity is bei~g made by
the U.S.Geological Survey under an appropriation of the Works Progress
Administration and the work is being based on the Colorado
grid.
The matter' of city surveys brings up the question regarding
sea level and ground level, or rather, whether grid scale should
be used, or a scale on a mean ground-level plane. It seems to me
that the importance of having the work tied in with the control net
far outweighs the need for exact ground level distances. A circular
letter was sent to a number of representative engineers and surveyors
to get a general recommendation on this very point. Most of
the replies that we received looked at the matter in the same way as
we had considered it. Actual lengths and areas can easily be determined
from a map made on the state grid even though the coordinates
may give slightly different results. Denver is probably at a higher
elevation than any other large city in the country and, if its engineers
find the use of the State grid satisfactory for their work,
it should be equally so for any other such city in the country.. .
I here ya Mighty...
I just did a quick tabulation of my CURRENT projects (ones that I will be working on this coming week)
#1. PLSS and Mineral Survey Retracement (long term)
Overall scope ~8 or 9 square miles
Elevation range ~6180 to ~9360
Relief ~3180
#2. PLSS Retracement (short term)
Overall scope ~11 square miles
Elevation range ~5540 to ~6960
Relief ~1420
#3. PLSS Retracement (short term)
Overall scope ~10 Square miles
Elevation range ~4600 to ~6500
Relief ~1900
#4. PLSS Retracement (long term)
Overall scope ~12 Square miles
Elevation range ~5500 to ~8200
Relief ~2700
There is another [LONG Term] Project that may or may not hit the front burner this week:
#5. PLSS & Mineral Survey Retracement
Overall scope ~275 Square miles
Elevation range ~4200 to ~6500
Relief ~2300
Ain't no "couple sq. mile pancake [Texas] surveys" on my desk this year. Of course that could change, but a "pancake survey" out here usually has about 500 feet of relief. The last "little" project was less than a square mile in Utah last year, and it had about 1600 feet of relief.
B-)
Loyal
Even doing those jobs with conventional equipment will reveal the distortions
Since there are places in Texas where the combined factor is acceptably near enough to 1 that grid and ground measurements are functionally equivalent, clearly LDP are a fools errand. Carry on.
Shawn Billings, post: 375719, member: 6521 wrote: Since there are places in Texas where the combined factor is acceptably near enough to 1 that grid and ground measurements are functionally equivalent, clearly LDP are a fools errand. Carry on.
Well, not exactly, when state plane scales are very close to 1 then it is a LPD
I work from the west coast to the divide and in both TM and Lambert states. Most blanket statements about geodesy fall apart at least some of the places I work. This used to think the 1:10,000 distortion touted by the NGS was bull. As with many things I came to realize I simply misread the claim.
Projecting from geographic to the defined grids of the lower 48 will not distort beyond 1 in 10k. During the process of mutilating to ground we see greater distortions. Mathematical violence is a tradeoff. The key is to stay inside the error budget and still meet the money budget...
The 1 in 10k I was told way back was the error you could expect to see as you survey near the edges of a zone conventionally.
However, it was always difficult to tell if your "error" was caused by your survey, errors in the NGS monuments, not using all the math that should be applied to each course (you aren't really surveying in a grid afterall) or a combination of all of the above.
With GPS the 1 in 10k became moot, you are only projecting from "perfect" data so there is no real "error" anymore, clearly the 1 in 10k has nothing to do with ground to grid, at least I've never seen such a small scale.
I never put too much time thinking about it, we never closed that bad anyway, even near the edges, unless it was to a third order point, and we usually tried to go "over" those with our traverses.
Loyal, as usual, is pretty much on target, with one little exception in the good old state of North Carolina.
NC is really big enough north to south to have two Lambert zones, but the state decided long ago that the problem of worse than 1:10,000 plane to ellipsoid was easier to live with than having two Lambert zones. Hence, the southeastern part of the state, which borders the Atlantic Ocean and is flat as a pancake, also produces worse than 1:10,000 plane to ellipsoid accuracy.
Since much of the area also has negative ellipsoid heights, ground to grid is even worse. For example, for NGS mark AJ4962, the scale factor is 1.00014613, the elevation factor is 1.00000527, and the combined factor is 1.00015140. That makes grid to ellipsoid accuracy 1:6,843 and grid to ground accuracy 1:6,605.
So unadjusted state plane figures can produce worse than 1:10,000 even in flat-as-a-pancake environments.
MathTeacher, post: 375891, member: 7674 wrote: Loyal, as usual, is pretty much on target, with one little exception in the good old state of North Carolina.
NC is really big enough north to south to have two Lambert zones, but the state decided long ago that the problem of worse than 1:10,000 plane to ellipsoid was easier to live with than having two Lambert zones. Hence, the southeastern part of the state, which borders the Atlantic Ocean and is flat as a pancake, also produces worse than 1:10,000 plane to ellipsoid accuracy.
Since much of the area also has negative ellipsoid heights, ground to grid is even worse. For example, for NGS mark AJ4962, the scale factor is 1.00014613, the elevation factor is 1.00000527, and the combined factor is 1.00015140. That makes grid to ellipsoid accuracy 1:6,843 and grid to ground accuracy 1:6,605.
So unadjusted state plane figures can produce worse than 1:10,000 even in flat-as-a-pancake environments.
It's unusual to see scale factors here better than 1/5000 and they can get to 1/1250, I don't think the old 1:10000 statement had anything to do with ground vs grid
MightyMoe, post: 375897, member: 700 wrote: It's unusual to see scale factors here better than 1/5000 and they can get to 1/1250, I don't think the old 1:10000 statement had anything to do with ground vs grid
You're absolutely Right Mighty!
It NEVER did...
The 1:10,000 varies by zone, as I pointed out in my Wyoming example, and Math Teacher did for North Caroline.
The ol' 1:10,000 (give or take) statement ALWAYS referred to the relationship of the Developed Surface (GRID surface) and the surface of the underlying spheroid/ellipsoid ('sea level' for NAD27 [more or less]). Which is in fact, two theoretical surfaces that never see the light of day in most of the country.
Grid to Ground is MUCH more important to modern surveyors, than it was to "engineers" in Denver back in 1937.
Here's a piece of the NGS Data Sheet for McDonnell in downtown Denver:
1 National Geodetic Survey, Retrieval Date = JUNE 6, 2016
KK2099 ***********************************************************************
KK2099 CBN - This is a Cooperative Base Network Control Station.
KK2099 DESIGNATION - MCDONNELL
KK2099 PID - KK2099
KK2099 STATE/COUNTY- CO/DENVER
KK2099 COUNTRY - US
KK2099 USGS QUAD - FORT LOGAN (1994)
KK2099
KK2099 *CURRENT SURVEY CONTROL
KK2099 ______________________________________________________________________
KK2099* NAD 83(2011) POSITION- 39 44 34.68961(N) 105 00 03.94526(W) ADJUSTED
KK2099* NAD 83(2011) ELLIP HT- 1570.549 (meters) (06/27/12) ADJUSTED
KK2099* NAD 83(2011) EPOCH - 2010.00
KK2099* NAVD 88 ORTHO HEIGHT - 1587.6 (meters) 5209. (feet) GPS OBS
KK2099 ______________________________________________________________________
KK2099 NAVD 88 orthometric height was determined with an earlier geoid model
KK2099 NAD 83(2011) X - -1,271,464.369 (meters) COMP
KK2099 NAD 83(2011) Y - -4,744,806.603 (meters) COMP
KK2099 NAD 83(2011) Z - 4,057,086.731 (meters) COMP
KK2099 LAPLACE CORR - -8.29 (seconds) DEFLEC12B
KK2099 GEOID HEIGHT - -17.052 (meters) GEOID12B
KK2099
KK2099 Network accuracy estimates per FGDC Geospatial Positioning Accuracy
KK2099 Standards:
KK2099 FGDC (95% conf, cm) Standard deviation (cm) CorrNE
KK2099 Horiz Ellip SD_N SD_E SD_h (unitless)
KK2099 -------------------------------------------------------------------
KK2099 NETWORK 0.45 0.92 0.20 0.16 0.47 -0.01031799
KK2099 -------------------------------------------------------------------
KK2099 Click here for local accuracies and other accuracy information.
KK2099
KK2099
KK2099.The horizontal coordinates were established by GPS observations
KK2099.and adjusted by the National Geodetic Survey in June 2012.
KK2099
KK2099.NAD 83(2011) refers to NAD 83 coordinates where the reference frame has
KK2099.been affixed to the stable North American tectonic plate. See
KK2099.NA2011 for more information.
KK2099
KK2099.The horizontal coordinates are valid at the epoch date displayed above
KK2099.which is a decimal equivalence of Year/Month/Day.
KK2099
KK2099.The orthometric height was determined by GPS observations and a
KK2099.high-resolution geoid model.
KK2099
KK2099.Significant digits in the geoid height do not necessarily reflect accuracy.
KK2099.GEOID12B height accuracy estimate available here.
KK2099
KK2099.The X, Y, and Z were computed from the position and the ellipsoidal ht.
KK2099
KK2099.The Laplace correction was computed from DEFLEC12B derived deflections.
KK2099
KK2099.The ellipsoidal height was determined by GPS observations
KK2099.and is referenced to NAD 83.
KK2099
KK2099. The following values were computed from the NAD 83(2011) position.
KK2099
KK2099; North East Units Scale Factor Converg.
KK2099;SPC CO C - 516,908.805 957,164.206 MT 0.99999862 +0 18 52.8
KK2099;SPC CO C - 1,695,891.64 3,140,296.23 sFT 0.99999862 +0 18 52.8
KK2099;UTM 13 - 4,399,229.964 499,906.104 MT 0.99960000 -0 00 02.5
KK2099
KK2099! - Elev Factor x Scale Factor = Combined Factor
KK2099!SPC CO C - 0.99975367 x 0.99999862 = 0.99975229
KK2099!UTM 13 - 0.99975367 x 0.99960000 = 0.99935377
KK2099
Lets say that the City "Blocks" are 500 feet on the sides (looking at Google Earth, it appears that they vary quite a bit), but 500 feet will serve for this example.
So, 500 feet measured ON THE GROUND from McDonnel computes as follows:
500.000 Chain/Tape/EDM/GPS on GROUND
499.877 on NAD83 Ellipsoid
499.876 On SPC Grid
500.000/499.876 = 1.000 248 = 1:4,036
Now 0.12 per 500 (1:4036) was apparently A-Okay for the "engineers" in Denver back in 1937, and is probably Okay for the GIS even today. But is it OKAY for Land Surveyors working in Downtown Denver TODAY?
I dunno...you tell me.
I suspect that the Denver Folks use a "combined factor" to SCALE Colorado SPCs up to the real world, but maybe not!
😀
Loyal
Right, Loyal and Moe. To go from ground to ellipsoid, multiply ground by elevation factor and to then go from ellipsoid to grid, multiply that result by scale factor. Hence the combined factor which is the product of the scale factor and the elevation factor. Multiplying ground by combined factor takes ground to grid. But everyone knows that.
State planes are designed so that the scale factor, which relates grid to ellipsoid, is always between 0.9999 and 1.0001. That means that a grid distance used in place of an ellipsoid distance would show 1:10,000 or better accuracy when compared to the actual ellipsoid distance.
In North Carolina, though. because the southeastern part of the state is outside the 1:10,000 distance from the central parallel, the agreement between grid distances and ellipsoid distances is worse than 1:10,000.
In Loyal's example point, MR0820, the scale factor is 0.99995684, which is between 0.9999 and 1.0001. That means that the 1:10,000 design criteria for the Wyoming state plane is met at that point.
1:10000 is the lower limit of much of state plane control, it is usually better that that, but it is rare that I see it get better than 1:100000.......of course that's surveying conventionally between NGS 27 monuments.
MathTeacher, post: 375909, member: 7674 wrote: Right, Loyal and Moe. To go from ground to ellipsoid, multiply ground by elevation factor and to then go from ellipsoid to grid, multiply that result by scale factor. Hence the combined factor which is the product of the scale factor and the elevation factor. Multiplying ground by combined factor takes ground to grid. But everyone knows that.
State planes are designed so that the scale factor, which relates grid to ellipsoid, is always between 0.9999 and 1.0001. That means that a grid distance used in place of an ellipsoid distance would show 1:10,000 or better accuracy when compared to the actual ellipsoid distance.
In North Carolina, though. because the southeastern part of the state is outside the 1:10,000 distance from the central meridian, the agreement between grid distances and ellipsoid distances is worse than 1:10,000.
In Loyal's example point, MR0820, the scale factor is 0.99995684, which is between 0.9999 and 1.0001. That means that the 1:10,000 design criteria for the Wyoming state plane is met at that point.
Check out some grid factors in central montana
MightyMoe, post: 375912, member: 700 wrote: Check out some grid factors in central montana
Here's a pretty good one for them to look at Mighty:
RW0513 ***********************************************************************
RW0513 DESIGNATION - YOGO
RW0513 PID - RW0513
RW0513 STATE/COUNTY- MT/JUDITH BASIN
RW0513 COUNTRY - US
RW0513 USGS QUAD - YOGO PEAK (1995)
RW0513
RW0513 *CURRENT SURVEY CONTROL
RW0513 ______________________________________________________________________
RW0513* NAD 83(1992) POSITION- 46 55 38.83569(N) 110 32 32.95356(W) ADJUSTED
RW0513* NAVD 88 ORTHO HEIGHT - 2683.8 (meters) 8805. (feet) VERTCON
RW0513 ______________________________________________________________________
RW0513 GEOID HEIGHT - -11.155 (meters) GEOID12B
RW0513 LAPLACE CORR - -4.43 (seconds) DEFLEC12B
RW0513 HORZ ORDER - THIRD
RW0513
RW0513.The horizontal coordinates were established by classical geodetic methods
RW0513.and adjusted by the National Geodetic Survey in July 1992.
RW0513.
RW0513.The NAVD 88 height was computed by applying the VERTCON shift value to
RW0513.the NGVD 29 height (displayed under SUPERSEDED SURVEY CONTROL.)
RW0513
RW0513.Significant digits in the geoid height do not necessarily reflect accuracy.
RW0513.GEOID12B height accuracy estimate available here.
RW0513
RW0513.The Laplace correction was computed from DEFLEC12B derived deflections.
RW0513
RW0513. The following values were computed from the NAD 83(1992) position.
RW0513
RW0513; North East Units Scale Factor Converg.
RW0513;SPC MT - 298,045.424 520,655.824 MT 0.99939374 -0 45 45.3
RW0513;SPC MT - 977,839.32 1,708,188.40 iFT 0.99939374 -0 45 45.3
RW0513;UTM 12 - 5,197,204.010 534,829.709 MT 0.99961491 +0 20 03.2
RW0513
RW0513! - Elev Factor x Scale Factor = Combined Factor
RW0513!SPC MT - 0.99958124 x 0.99939374 = 0.99897524
RW0513!UTM 12 - 0.99958124 x 0.99961491 = 0.99919631
RW0513
RW0513: Primary Azimuth Mark Grid Az
RW0513:SPC MT - NEIHART 2 313 57 58.8
RW0513:UTM 12 - NEIHART 2 312 52 10.3
RW0513
RW0513|---------------------------------------------------------------------|
RW0513| PID Reference Object Distance Geod. Az |
RW0513| dddmmss.s |
RW0513| RW0512 NEIHART 2 APPROX. 6.7 KM 3131213.5 |
RW0513|---------------------------------------------------------------------|
RW0513
RW0513 SUPERSEDED SURVEY CONTROL
RW0513
RW0513 NAD 83(1986)- 46 55 38.83218(N) 110 32 32.93716(W) AD( ) 3
RW0513 NAD 27 - 46 55 38.97146(N) 110 32 30.17948(W) AD( ) 3
RW0513 NGVD 29 (07/19/86) 2682.6 (m) 8801. (f) VERT ANG
RW0513
RW0513.Superseded values are not recommended for survey control.
RW0513
RW0513.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.
RW0513.See file dsdata.txt to determine how the superseded data were derived.
RW0513
RW0513_U.S. NATIONAL GRID SPATIAL ADDRESS: 12TWS3482997204(NAD 83)
RW0513
RW0513_MARKER: 57 = LOOKOUT TOWER
RW0513
RW0513 HISTORY - Date Condition Report By
RW0513 HISTORY - 1960 FIRST OBSERVED USGS
RW0513
RW0513 STATION DESCRIPTION
RW0513
RW0513'DESCRIBED BY US GEOLOGICAL SURVEY 1960
RW0513'LOCATED IN JUDITH BASIN COUNTY, MONTANA, IN THE SW. 1/4 OF SEC. 35,
RW0513'T 14 N, R 9 E, AND IS THE U.S.F.S. LOOKOUT TOWER ON YOGO PEAK.
RW0513'
RW0513'TO REACH FROM THE POST OFFICE AT NEIHART, MONTANA, GO S. ON U.S.
RW0513'HIGHWAY 89 8.7 MI., TURN LEFT (SE.) AND GO 1.2 MI. TO RD. FORK, TAKE
RW0513'LEFT FORK (NE.) AND GO 8.5 MI. TO RD. FORK, TAKE RIGHT FORK (E.) AND
RW0513'GO 2.2 MI. TO RD. FORK IN SADDLE BETWEEN TEPEE BUTTE AND YOGO PEAK,
RW0513'TAKE RIGHT FORK AND GO 0.5 MI. TO YOGO LOOKOUT TOWER AND STATION.
RW0513'
RW0513'STATION MARK--CENTER OF TOWER AS FORMED BY DIAGONALS BETWEEN CONCRETE
RW0513'SUPPORTING PILLARS FOR TOWER LEGS.
Grid to Ground 1:975 Whoopie,!
Although the Grid/Ellipsoid ain't so bad (1:1648)
On a semi-related note:
I wonder if Kent has that Shackleford system worked out yet?
o.O
Loyal
