I've been practicing with my x-90 OPUS receiver and want to use the results on my boundary survey. Of course, the GPS bearings are quite different than the deed bearings. I observed my start point for 2.5 hours and my BS point for about an hour. The 1st point is for elevation control and the second was just for the backsight. My results were pretty good with very small uncertainties.
My question is this: How would I write my "metadata" on the plan so that any other surveyor would know what I'm talking about.
Here are my results:
SOFTWARE: page5 1209.04 master93.pl 022814 START: 2014/06/05 15:31:00
EPHEMERIS: igu17954.eph [ultra-rapid] STOP: 2014/06/05 17:59:30
NAV FILE: brdc1560.14n OBS USED: 4848 / 5408 : 90%
ANT NAME: CHCX90D-OPUS NONE # FIXED AMB: 36 / 39 : 92%
ARP HEIGHT: 2.0000 OVERALL RMS: 0.015(m)
REF FRAME: NAD_83(2011)(EPOCH:2010.0000) IGS08 (EPOCH:2014.4266)
X: 949534.105(m) 0.007(m) 949533.278(m) 0.007(m)
Y: -4764683.933(m) 0.017(m) -4764682.508(m) 0.017(m)
Z: 4119484.718(m) 0.009(m) 4119484.655(m) 0.009(m)
LAT: 40 29 5.96373 0.008(m) 40 29 5.99499 0.008(m)
E LON: 281 16 14.09973 0.005(m) 281 16 14.07712 0.005(m)
W LON: 78 43 45.90027 0.005(m) 78 43 45.92288 0.005(m)
EL HGT: 604.391(m) 0.019(m) 603.165(m) 0.019(m)
ORTHO HGT: 636.713(m) 0.034(m) [NAVD88 (Computed using GEOID12A)]
UTM COORDINATES STATE PLANE COORDINATES
UTM (Zone 17) SPC (3702 PA S)
Northing (Y) [meters] 4484065.063 128334.849
Easting (X) [meters] 692446.159 516963.583
Convergence [degrees] 1.47462525 -0.63543888
Point Scale 1.00005590 0.99995968
Combined Factor 0.99996109 0.99986488
US NATIONAL GRID DESIGNATOR: 17TPE9244684065(NAD 83)
BASE STATIONS USED
PID DESIGNATION LATITUDE LONGITUDE DISTANCE(m)
DM4700 PAJP PUNXSUTAWNEY CORS ARP N405644.654 W0785703.370 54485.9
DK3589 HRN6 HAWK RUN 6 CORS ARP N405240.217 W0781052.575 63649.0
AF9653 PSU1 PENN STATE UNIV CORS ARP N404824.810 W0775059.267 82548.6
NEAREST NGS PUBLISHED CONTROL POINT
KX0603 64 N402909.49 W0784330.74 372.8
I left some out but this is the meat of it.
Anyone have a nice, succinct way of stating this on a plan? I don't normally use SPC or GPS for my boundary work but I'd like to start.
I usually provide the meta data as NC specs
Grid Tie note
Class of survey
Positional tolerance - .05
GPS method - opus
Datum- nad 83 NC grid (2011)
Geoid-12a
Date of survey- June 12,2014
Units - us ft
Then provide two grid coordinates on survey. I pick two corners that are near my opus points
And are with in a distance that grid calculation would not effect the label. Or provide ties to your opus points if permanent enough for your use.
Ok, so you have state plane coordinates (grid) and you'll need to get them to ground to do boundary determination and match the deed distances. So you'll scale them by the ground scale factor (1.00005590). I usually scale from the 0,0 coordinate instead of a central point. Then I will do the boundary analysis as usual but when it comes time for my basis of bearings I will say something like:
"Bearings are based on the north line of Section XX being XX-XX-XX.XX as determined using such and such system(VRS, OPUS). All work was performed in such and such coordinate system and such and such datums. Elevations were computed using GEOID2012A. All distances shown are ground distances using a ground scale factor of 1.00005590."
I would love to hear criticisms of this approach.
The objective of course is to make your work reproducible by the next person who comes along. Exactly what information to include to achieve that goal is an excellent question to ask.
For guidance I suggest this document from the NC Board. (Proper Survey Ties)
Those rules do not specifically apply anywhere other than NC; but, they will give a pretty good idea of what our board expects. And let's face it, the exact details may vary slightly from jurisdiction to jurisdiction; but, the general concepts are the same all around the world.
Hope that helps.
Larry P
I usually include the following note:
"Basis of Bearings: Grid north, Arkansas coordinate system, South Zone, by GPS observation."
Your note of course would be different. You can compute true north using the data from your report, but you will need to state the convergence on the the drawing so others can follow you.
Just FYI: I'm normally skeptical of short static sessions for elevations. I've had decent results with 6 hour sessions; but usually I prefer OPUS-RS for short observations when looking for good verticals.
You might be fine though.
Forgot CSF
We have found the 0.04!
Combined Factor 0.99996109 UTM COORDINATES
UTM grid 999.96 = 1000.00 GROUND
We don't see UTM scale better than state plane scale around here. I'd just use unscaled UTM if its a small project less than 40 acres. Your state plane grid/ground error is about 0.14 in 1000 which is not terrible for a suburban boundary but some around here will go bananas if you don't correct it.
"Just FYI: I'm normally skeptical of short static sessions for elevations. I've had decent results with 6 hour sessions; but usually I prefer OPUS-RS for short observations when looking for good verticals."
Does the fact that he stated that this was a boundary survey affect your question?
> I would love to hear criticisms of this approach.
I think the only critiques you'll get are those that do not understand the concept of a site calibration (or localization in Topconese). They don't own a base station, just hook up to the local RTN and go. Us guys in the boonies don't have that luxury.
But I suspect our newbie may want to re-think the one point calibration for horizontal. You need some rotation to a known bearing (deed perhaps). One point is ok for vertical, but better check into something else or run OPUS on multiple points. Taking coordinates to 0,0 eliminates any confusion with SPC.
Skip the meta data, you already brought it to ground using your combined scale factor. So the SPC's are no good. Just say that if you want warm & fuzzies, but you're still on the hook for your survey.
Now, I'll get beat up.... 😉
He said that he observed both his instrument start point and backsight point with GPS and shot somewhat long observations with both. So he has a rotation, but you're right.. starting with just 1 point wouldn't do you much good.
There are a bazillion ways to skin this cat. The only thing I would consider changing is your statement regarding scale. I call it Combined Scale Factor or Combined Factor depending on the locale. I also give the formula as SPC NORTHING / CSF = GROUND NORTHING. It eliminates questions.
I am
actually using the vert from the 2.5 hour session. The job is for an architect and they wanted contours and boundary and basically a site plan. I started off using whatever coordinates OPUS gave me. Checked them in the field +/- a few "hundies" and said, "Hey, that's better than some of the other points I find" and went with it. Now I don't want to go twisting and turning on these points and texts and such. I started from a couple pretty good points and nobody is even asking for SPCs. They're architects.
I now have a survey and the whole shebang and would like to make note of my bearing base. You can get a bearing out of a deed and just go with it, sure. Twist it so it matches, sure. But going in the way I did, I'd like to keep it going and have at least some clue as to making note of how I did it without writing a book about it on my map. Also, I could give another surveyor one point coordinate, he could go find it with whatever RTK unit he has then find the rest by perhaps conventional means.
Remember, as well, that there are other points in the neighborhood and some of them are displaced and some are ok. My points are parallel with the streets and the streets were averaged over a given distance etc etc. I have legitimate points set under satisfactory conditions and I started with GPS.
If it must be a big deal about supercharged point networks and 17 6 hour sessions with at least 8 units running at all times, I'm out. I'm out, at least, until I can figure out a way to use this GPS for things other than ECs. The Published USGS points were good until they switched the system around and now the coordinates are different but that doesn't make them invalid.
Maybe I should take a class.
USGS ?
>Published USGS points were good
Depends on what you mean by published. If you find NGS data sheets for these points with NGVD29 or NAVD88 elevations, as appropriate for your area's flood maps, then great. NGS has good data sheets in their data base for only a minority of the USGS disks. Most USGS disks were never measured to NGS(former C&GS) standards.
USGS disks often have old elevations stamped on them that do not correspond to NGS elevations, and unless you know the local flood maps are based on those numbers they should not be used.
Nothing
I did nothing to the points. I did not use a scale factor. I just punched the numbers in from the report. The distance and elevation difference were within tolerance.
Thanks
I appreciate the responses.
I'll keep working at it and studying it.
Thanks
Matt, if you are just reporting bearings and distances on a survey then just state the state plane zone and how the distances are computed, for instance if they are state plane unadjusted: state that the bearings and distances are xxxx state plane zone. If they are surface/ground distances give a factor to calculate between state plane and surface.
If for some reason on the survey you report coordinates then much more metadata should be given.
