Using State Plane Coordinates...Educational Endeavor

Don't try a solar observation using an instrument with EDM in it unless you have the proper objective filter - you'll fry the sensors. The projection method is only for instruments that don't have the EDM.

I've found Polaris observations to be much easier and much more accurate at my skill level than solars because a) time is less critical and b) you are aiming at a point, not the edge of the sun disk. The main drawback for me is that lighting the scope's reticule is a hassle if not built-in, and you don't want to block the objective lens (especially by something asymmetrical). I have had best results from shortly before sunset until it gets dark. With care you should be able to get a Polaris azimuth within your instrument's basic pointing accuracy. Don't forget the Laplace correction.

For SPC you need to be aware of "grid to ground" conversions. The convergence angle results from the distortions of squeezing a round earth onto a flat map. Once you are on the map grid, angles remain unaffected, but getting on and off the grid needs that correction. Likewise, there is a factor for lengths due to the stretching/compression of the map projection. And you have to account for your elevation above sea level.

Surveyors' plats don't always tell you enough to get an absolute azimuth off them, since they are mostly concerned with relative values. Careful study of the one you have may or may not let you use that for orientation.

For elevations or for horizontal positions, it is quite confusing to have something that looks like it could be right but actually isn't.

For elevations, if you don't have a benchmark nearby that is as accurate as you will ever want things, it is probably best to adopt a local 100 ft assumed elevation on some long-term stable point for your work, and if you later can find the actual elevation of that point you can easily convert.

For horizontal, you may want to show ground-level positions, and do the conversion from SPC grid to ground. When you do that, PLEASE subtract off some leading digits from the ground values so you don't confuse them with real SPC. Applying a combined factor to the SPC to get ground values, and not subtracting off, is a common practice, particularly in DOT work, but risks a lot of confusion for anyone not immersed in that system.

Whatever kind of coordinates you decide to work in, record careful notes (metadata) so there will be no ambiguity when you look back later.

Well,,, why can't you traverse? It's not far and you can set on the monument and backsite the AZ mark and have good direction. That's how we used to do it all the time. Easy;-)

> Don't try a solar observation using an instrument with EDM in it unless you have the proper objective filter - you'll fry the sensors. The projection method is only for instruments that don't have the EDM.
Yup; Got that one down. Understood.

> For SPC you need to be aware of "grid to ground" conversions. The convergence angle results from the distortions of squeezing a round earth onto a flat map. Once you are on the map grid, angles remain unaffected, but getting on and off the grid needs that correction. Likewise, there is a factor for lengths due to the stretching/compression of the map projection. And you have to account for your elevation above sea level.

> For horizontal, you may want to show ground-level positions, and do the conversion from SPC grid to ground. When you do that, PLEASE subtract off some leading digits from the ground values so you don't confuse them with real SPC. Applying a combined factor to the SPC to get ground values, and not subtracting off, is a common practice, particularly in DOT work, but risks a lot of confusion for anyone not immersed in that system.
>
> Whatever kind of coordinates you decide to work in, record careful notes (metadata) so there will be no ambiguity when you look back later.

I haven't been able to find the Grid Scale Factor for my longitude anywhere on Vermont's GIS site, or NGS. There's a bunch of "converters" for UTM to SPC, but not grid factor. Where do I find this?

>
> Surveyors' plats don't always tell you enough to get an absolute azimuth off them, since they are mostly concerned with relative values. Careful study of the one you have may or may not let you use that for orientation.
>

Not sure what you mean by "absolute azimuth", but there's one line, which happens to be the State Highway ROW that has been measured to the nearest second, and, according to the plat, says the bearings refer to Vermont Grid North, "as established by OPUS Observations yada yada". Have no idea if that's good enough. The bearing happens to be my first backlight from my proposed POB.

It might be easy, or might not, depending on the terrain. Make an estimate in Star*Net of the accuracy you would end up with in position and azimuth, based on approximate setup positions and the number of shots and your typical accuracy per measurement.

> Well,,, why can't you traverse? It's not far and you can set on the monument and backsite the AZ mark and have good direction. That's how we used to do it all the time. Easy;-)

Thanks for your confidence. Technically, with the direction accuracy of my TS, I'd expect to end up less than 1.25' from where I should be in 8000' (before adjustment). It'd take at least 8 -10 occupations, but I don't trust my abilities to meet that target.

Besides, it's all along a State Highway, and I don't have a hard hat and one of those cool reflective vests yet.:-D

You indicate that NGS PID AE6516 is the nearest "Control" Station.

Here's the NGS Data Sheet:

The NGS Data Sheet

See file  dsdata.txt for more information about the datasheet.
PROGRAM = datasheet95, VERSION = 8.5
1        National Geodetic Survey,   Retrieval Date = OCTOBER 20, 2014
 AE6516 ***********************************************************************
 AE6516  DESIGNATION -  206 VT 102
 AE6516  PID         -  AE6516
 AE6516  STATE/COUNTY-  VT/WINDSOR
 AE6516  COUNTRY     -  US
 AE6516  USGS QUAD   -  WOODSTOCK NORTH (1976)
 AE6516
 AE6516                         *CURRENT SURVEY CONTROL
 AE6516  ______________________________________________________________________
 AE6516* NAD 83(2011) POSITION- 43 39 18.05918(N) 072 33 56.79400(W)   ADJUSTED  
 AE6516* NAD 83(2011) ELLIP HT-   236.399 (meters)        (06/27/12)   ADJUSTED
 AE6516* NAD 83(2011) EPOCH   -  2010.00
 AE6516* NAVD 88 ORTHO HEIGHT -   263.8   (meters)      865.    (feet) GPS OBS   
 AE6516  ______________________________________________________________________
 AE6516  NAVD 88 orthometric height was determined with geoid model    GEOID96
 AE6516  GEOID HEIGHT    -        -27.45  (meters)                     GEOID96
 AE6516  GEOID HEIGHT    -        -27.40  (meters)                     GEOID12A
 AE6516  NAD 83(2011) X  -  1,384,857.995 (meters)                     COMP
 AE6516  NAD 83(2011) Y  - -4,409,854.632 (meters)                     COMP
 AE6516  NAD 83(2011) Z  -  4,380,601.985 (meters)                     COMP
 AE6516  LAPLACE CORR    -         -4.04  (seconds)                    DEFLEC12A
 AE6516
 AE6516  FGDC Geospatial Positioning Accuracy Standards (95% confidence, cm)
 AE6516  Type                                         Horiz  Ellip  Dist(km)
 AE6516  -------------------------------------------------------------------
 AE6516  NETWORK                                       1.07   1.55
 AE6516  -------------------------------------------------------------------
 AE6516  MEDIAN LOCAL ACCURACY AND DIST (005 points)   0.95   1.41      8.74
 AE6516  -------------------------------------------------------------------
 AE6516  NOTE: Click here for information on individual local accuracy
 AE6516  values and other accuracy information.
 AE6516
 AE6516
 AE6516.The horizontal coordinates were established by GPS observations
 AE6516.and adjusted by the National Geodetic Survey in June 2012.
 AE6516
 AE6516.NAD 83(2011) refers to NAD 83 coordinates where the reference 
 AE6516.frame has been affixed to the stable North American tectonic plate. See 
 AE6516.NA2011 for more information. 
 AE6516
 AE6516.The horizontal coordinates are valid at the epoch date displayed above
 AE6516.which is a decimal equivalence of Year/Month/Day.
 AE6516
 AE6516.The orthometric height was determined by GPS observations and a
 AE6516.high-resolution geoid model.
 AE6516
 AE6516.The X, Y, and Z were computed from the position and the ellipsoidal ht.
 AE6516
 AE6516.The Laplace correction was computed from DEFLEC12A derived deflections.
 AE6516
 AE6516.The ellipsoidal height was determined by GPS observations
 AE6516.and is referenced to NAD 83.
 AE6516
 AE6516. The following values were computed from the NAD 83(2011) position.
 AE6516
 AE6516;                    North         East     Units Scale Factor Converg.
 AE6516;SPC VT       -   128,313.204   494,694.066   MT  0.99996463   -0 02 43.5
 AE6516;SPC VT       -   420,974.24  1,623,008.78   sFT  0.99996463   -0 02 43.5
 AE6516;UTM  18      - 4,836,436.770   696,291.860   MT  1.00007395   +1 40 51.3
 AE6516
 AE6516!             -  Elev Factor  x  Scale Factor =   Combined Factor
 AE6516!SPC VT       -   0.99996293  x   0.99996463  =   0.99992756
 AE6516!UTM  18      -   0.99996293  x   1.00007395  =   1.00003688
 AE6516
 AE6516:                Primary Azimuth Mark                     Grid Az
 AE6516:SPC VT       -  206VT102 AZ MK                           146 18 10.6
 AE6516:UTM  18      -  206VT102 AZ MK                           144 34 35.8
 AE6516
 AE6516|---------------------------------------------------------------------|
 AE6516| PID    Reference Object                     Distance      Geod. Az  |
 AE6516|                                                           dddmmss.s |
 AE6516| AE6540 206VT102 AZ MK                      403.900 METERS 1461527.1 |
 AE6516|---------------------------------------------------------------------|
 AE6516
 AE6516                          SUPERSEDED SURVEY CONTROL
 AE6516
 AE6516  NAD 83(2007)-  43 39 18.05951(N)    072 33 56.79468(W) AD(2002.00) 0
 AE6516  ELLIP H (02/10/07)  236.414  (m)                       GP(2002.00)    
 AE6516  ELLIP H (06/04/02)  236.408  (m)                       GP(       ) 4 2
 AE6516  NAD 83(1996)-  43 39 18.05955(N)    072 33 56.79526(W) AD(       ) 1
 AE6516  ELLIP H (02/18/98)  236.439  (m)                       GP(       ) 4 1
 AE6516
 AE6516.Superseded values are not recommended for survey control.
 AE6516
 AE6516.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.
 AE6516.See file dsdata.txt to determine how the superseded data were derived.
 AE6516
 AE6516_U.S. NATIONAL GRID SPATIAL ADDRESS: 18TXP9629136436(NAD 83)
 AE6516
 AE6516_MARKER: DV = VERTICAL CONTROL DISK
 AE6516_SETTING: 17 = SET INTO TOP OF METAL PIPE DRIVEN INTO GROUND
 AE6516_STAMPING: 206-VT-102
 AE6516_MARK LOGO: ATSM
 AE6516_MAGNETIC: B = BAR MAGNET IMBEDDED IN MONUMENT
 AE6516_STABILITY: D = MARK OF QUESTIONABLE OR UNKNOWN STABILITY
 AE6516_SATELLITE: THE SITE LOCATION WAS REPORTED AS SUITABLE FOR
 AE6516+SATELLITE: SATELLITE OBSERVATIONS - June 18, 1997
 AE6516
 AE6516  HISTORY     - Date     Condition        Report By
 AE6516  HISTORY     - UNK      MONUMENTED       NPS
 AE6516  HISTORY     - 19970618 GOOD             VTGS
 AE6516
 AE6516                          STATION DESCRIPTION
 AE6516
 AE6516'DESCRIBED BY VERMONT GEODETIC SURVEY 1997 (DJM)
 AE6516'GENERAL LOCATION WOODSTOCK, VT.  0.2 MI (0.3 KM) SOUTH OF THE
 AE6516'WOODSTOCK/POMFRET TOWN LINE.  MARK IS AN APPALACHIAN NATIONAL SCENIC
 AE6516'TRAIL SURVEY MARKER.  TO REACH FROM THE INTERSECTION OF U.S.  ROUTE 4
 AE6516'AND VT ROUTE 12 IN THE CENTER OF WOODSTOCK VILLAGE, PROCEED NORTH ON
 AE6516'VT ROUTE 12 FOR 3.9 MI (6.3 KM) TO THE MARK ON THE RIGHT.  THE MARK IS
 AE6516'12 M (39.4 FT) SOUTHEAST OF THE INTERSECTION OF VT ROUTE 12 AND A
 AE6516'GRAVEL DRIVE, 10 M (32.8 FT) EAST NORTHEAST OF AND .8 M (2.6 FT) LOWER
 AE6516'IN ELEVATION THAN THE CENTERLINE OF VT ROUTE 12, AND .2 METERS (0.7
 AE6516'FT) WEST SOUTHWEST OF A FIBERGLASS WITNESS AND A METAL APPALACHIAN
 AE6516'TRAIL WITNESS.

That should give you everything you need to know (Azimuth Mark, Scale, Convergrncy, Laplace, etc...)

Loyal

As they told us out in Ft. Sill. You'll only do a sun shot twice without the sun filter. Once with the left eye and once with the right.

Thanks for your confidence. Technically, with the direction accuracy of my TS, I'd expect to end up less than 1.25' from where I should be in 8000' (before adjustment).

If all you want is good direction, I'd turn some angles from the monument, usually they were set nice and high and can see for miles, if you can see down that road to any opening near your project set a nice sight up and turn angles to it, then estimate the distance by scaling a distance on the quad or google and calc a "rough" plane coordinate and hold that position. Use that as a starting point and backsight the monument, a nice long backsight.

> You indicate that NGS PID E6516 is the nearest "Control" Station.
>
> Here's the NGS Data Sheet:
>
> AE6516
> AE6516; North East Units Scale Factor Converg.
> AE6516;SPC VT - 128,313.204 494,694.066 MT 0.99996463 -0 02 43.5
> AE6516;SPC VT - 420,974.24 1,623,008.78 sFT 0.99996463 -0 02 43.5
> AE6516;UTM 18 - 4,836,436.770 696,291.860 MT 1.00007395 +1 40 51.3
> AE6516
> AE6516! - Elev Factor x Scale Factor = Combined Factor
> AE6516!SPC VT - 0.99996293 x 0.99996463 = 0.99992756
> AE6516!UTM 18 - 0.99996293 x 1.00007395 = 1.00003688
> AE6516
> AE6516: Primary Azimuth Mark Grid Az
> AE6516:SPC VT - 206VT102 AZ MK 146 18 10.6
> AE6516:UTM 18 - 206VT102 AZ MK 144 34 35.8
> AE6516
> AE6516|---------------------------------------------------------------------|
> AE6516| PID Reference Object Distance Geod. Az |
> AE6516| dddmmss.s |
> AE6516| AE6540 206VT102 AZ MK 403.900 METERS 1461527.1 |
> AE6516|---------------------------------------------------------------------|
>
> That should give you everything you need to know (Azimuth Mark, Scale, Convergrncy, Laplace, etc...)
>
> Loyal

Thanks. I actually had printed that when I found the mark some time ago, but didn't read it all carefully then.
do I understand correctly that my grid factor to put into the instrument is .99996463?

Also, (in case I want to take up the challenge)...I've been to the spot but there's nothing there, but someone's grass next to their driveway. It says in the description there is a bar magnet embedded in the mark. Is this so surveyors can find these if they're buried somewhat? Would a metal detector do the trick? I certainly wouldn't want to go digging up a guys lawn.

Finally, do I read this right that there is another mark some 400 meters away to determine azimuth? That's straight down the side of a long stretch of the road. I'll look for it tonight (not that I'm getting sucked into attempting this traverse, mind you...this is only educational curiosity!)

Running your lat/long through CORPSCON I get a convergence angle of -0°03'27". The number on your adjoiners survey seems reasonable. I thought that a convergence angle of nearly 2° was a lot for a small eastern state. I also thought that convergence angle reported to the tenth of a degree was odd.

BTW- Convergence angle is a function of longitude. It is independent of elevation.

The 1.7 degrees is mapping angle for the UTM system listed, and not the SPC. To find out SPC use a utility like corpscon or the online conversions on the NGS web site. The data sheet for the station probably has the SPC values too.

I can probably help you if you want to send me an email maybe we can talk. I am up by Burlington, but might be able to help.

- jerry

Since this is your first rodeo, I'd highly recommend booking this traverse and logging the measured distances. Apply the scale factors later. If you make a mistake in application of the scale factor (very easy to do) at least you will have your original measurements.

This ain't Texas!

> If all you want is good direction, I'd turn some angles from the monument, usually they were set nice and high and can see for miles, if you can see down that road to any opening near your project set a nice sight up and turn angles to it, then estimate the distance by scaling a distance on the quad or google and calc a "rough" plane coordinate and hold that position. Use that as a starting point and backsight the monument, a nice long backsight.

Er, not exactly. I scouted the area. At least 10 setups up a curvy, hilly road. Then there's the problem of the monuments...I liked the "They were set high and see for miles" line...Nope. There's nothing there, either at the BM or at the AZ reference mark. Didn't have my tape or metal detector, and will return to look, but I'm not letting this endeavor interrupt my main challenge...the traverse of the property.

What do you guys do? Load up the truck with employees on the clock...head out to plan setting up on the mark by 7:30 am, traverse done by noon, only to have them call in at 3 pm telling you they can't find the bench marks? How do surveyors even stay in business?

This ain't Texas!

Nor Wyoming.
> What do you guys do? Load up the truck with employees on the clock...head out to plan setting up on the mark by 7:30 am, traverse done by noon, only to have them call in at 3 pm telling you they can't find the bench marks? How do surveyors even stay in business?
Almost nobody attempts to put their work on state plane without GPS. It is possible, of course.

This ain't Texas!

> Er, not exactly. I scouted the area. At least 10 setups up a curvy, hilly road. Then there's the problem of the monuments...I liked the "They were set high and see for miles" line...Nope. There's nothing there, either at the BM or at the AZ reference mark. Didn't have my tape or metal detector, and will return to look, but I'm not letting this endeavor interrupt my main challenge...the traverse of the property.
>
It's true that the old triangulation marks were set in high places, but even then often required a tower to get over trees (if there were any). What you have is a GPS monument, so not so likely to be set for triangulation. However, I'd expect that it was in an open area in 1997.

> What do you guys do? Load up the truck with employees on the clock...head out to plan setting up on the mark by 7:30 am, traverse done by noon, only to have them call in at 3 pm telling you they can't find the bench marks? How do surveyors even stay in business?

For one, we keep up with monuments we rely on frequently so that we can find them easily (this is where a surveyor's private records become invaluable - once you find this mark, make some reference notes of your own to find it again). Two, we show up with the tools needed (handheld GPS, metal locator, tape, compass, shovel). Three, we have moved to using precision GNSS so that we don't have to hunt for monuments. If the job requires precision Geodetic control, you do what needs to be done to provide that control. If it takes all day to find the monument and another to find the azimuth and then another to do the traverse, and that's the best option you have available, well then you do it.

An azimuth mark was established to provide azimuth for the station. The short distance is undoubtedly due to limited options. It should be verified by an astronomic observation. Note that the datasheet includes both the grid and geodetic azimiths as well as the site's Laplace correction. When you make an astronomic azimuth you convert it to geodetic using the Laplace correction then apply the convergence angle to get a plane azimuth.

When I worked in New England in the early 70s locating navigational aids we often looked for powker line rights of way and similar off road locations to minimize the number of points to be occupied. Working along narrow winding roads is inherently dangerous. Many state and local governments require permits to work in the right-of-way.

I never understood why anyone would not perform reconnaissance and mark setting first. Pre-planning with maps and now Google Earth must be supplemented with on the ground recon.

It is also possible to get intermediate checks to intersection stations (e.g. Church steeples, radio and water towers) published by NGS.

There is an NGS state advisor in Vermont. He could be quite helpful.

Looks like a short time window between leaves and snow falling.

Good luck,

DMM

This ain't Texas!

Oh, we do traverse in trees quite often, and brush line, sometimes for many miles, and yes we often do work early. Most of the old tri stations in the area I've occupied over the years and any occupied by GPS like that one was recently should be there, so we aren't surprised by a missing one (usually), 10 turns would take a little time, but if you aren't gathering distances and a state highway is there, not too bad, if you are doing it to learn its not a bad way to get SP bearings, do a solar at each end and there you are; hey you asked, it's how we work. And a good way to learn how to turn angles;-)

> Running your lat/long through CORPSCON I get a convergence angle of -0°03'27". The number on your adjoiners survey seems reasonable. I thought that a convergence angle of nearly 2° was a lot for a small eastern state. I also thought that convergence angle reported to the tenth of a degree was odd.
>
> BTW- Convergence angle is a function of longitude. It is independent of elevation.

So would you say that the survey done in 2013, calling out a "-0°03'" convergence angle, that he was just rounding, or could 27" of convergence be due to the difference in Longitude between the BM and the site (72°35'6", compared to 72°33'56"). I downloaded Corpscon but haven't figured out how to use it. Put it on the list.

Lacking any better azimuth information, would it be safe just to use his measured angle?

do I understand correctly that my grid factor to put into the instrument is .99996463?

You don't understand.

You would put 0.99996463 in your instrument if you were at approx. sea level. You put the combined factor in at the mark 0.99992756. This accounts for the elevation factor as well. If you want precision however each leg of your traverse will have a unique combined scale. This would be the average of the combined scale of the point at each end of each traverse leg. No one said it was easy. particularly without GPS. That's why not very many attempted to use state plane before GPS. 0.99996463 is only precise at the mark. You could try using one scale for you whole traverse and your result may be decent but using a unique scale for each leg is the way it works by the book.