Im curious as to what folks on here believe to be the correct bearing basis statement when your survey is based upon an OPUS solution?
I've seen this done so many different ways although I'm sure there is more than one correct way.
I don't worry about stating how bearings were established. I see the statement determined by "static GPS" or determined by "OPUS observations", etc, pretty routinely. But I never see anyone state "distances determined by Leica total station TPS-1200" or "distances reduced to horizontal Carlson SurvCE".
If my work is tied to State Plane, my standard statement is:
Bearings related to Grid North for the Texas Coordinate System of 1983, North Central Zone. Convergence at POB: +1å¡58'43".
Most of the time my work is tied to a local grid system with geodetic North at the origin of the system so my standard statement is:
Bearings related to a local grid having an origin of North Latitude 32å¡12'34.5678" and West Longitude 94å¡12'34.5678". Convergence at POB: -00å¡00'17".
Whether the bearings are from an inverse of two coordinates determined by OPUS or by some post processing software or by RTK or by Polaris or Solar observation of by gyroscope is of less consequence in my opinion.
One Opus solution does not give you a basis of bearing.
TXSurveyor, post: 416602, member: 6719 wrote: Im curious as to what folks on here believe to be the correct bearing basis statement when your survey is based upon an OPUS solution?
I've seen this done so many different ways although I'm sure there is more than one correct way.
The standard note I use is a variation of this:
Bearings of Lines refer to Grid North of the Texas Coordinate System of 1983 (South Central Zone) as computed from GPS vectors
In your case, it sounds as if you don't have any GPS vectors across your network, but are just constraining the network to two or more NAD83 positioned obtained on control points via OPUS.
In that case, I'd use a note along these lines
Bearings of lines in the following description [or on this map] refer to Grid North of the Texas Coordinate System of 1983 (identify zone) as derived from a network of conventional survey measurements constrained to the NAD83 positions, same epoch, of two [or give number] control points more than _________ ft. distant derived from more than ____ hrs. of GPS observations computed via the NGS OPUS Utility, between which the computed azimuth was estimated to have a standard error of _____ seconds of arc or less.
The note mainly just serves in that case to give an order of magnitude estimate of the uncertainties in the orientation of the overall network.
When I observe static the locations are shown on ghe drawing and mentioned along the boundary on the drawing and in the report as a WGS84 lat and long observation.
A Harris, post: 416635, member: 81 wrote: When I observe static the locations are shown on ghe drawing and mentioned along the boundary on the drawing and in the report as a WGS84 lat and long observation.
In my view, the object of notes like this is to demonstrate that the surveyor didn't just orient a large survey network or traverse by constraining to two OPUS-derived positions within shouting distance of each other and without regard to the uncertainties in the positions. It's really more of an assurance as to methods for the sake of future surveyors, i.e. to let them know that the whole works probably isn't FUBAR, unlike some of the wackier GPS-related notes I've seen over the years, that mainly just shouted "FUBAR Alert !"
TXSurveyor, post: 416602, member: 6719 wrote: Im curious as to what folks on here believe to be the correct bearing basis statement when your survey is based upon an OPUS solution?
I've seen this done so many different ways although I'm sure there is more than one correct way.
In Texas, you need only reference the system. Mine goes a little something like this:
BEARINGS are based on the Texas Coordinate System of 1983, Texas Central Zone per GPS observations. All coordinates are U.S. Survey Feet, NAD83(2011)Epoch 2010.0000 per static GPS observations and an OPUS solution through the NGS website. To get geodetic bearings, rotate the bearings shown/recited hereon, clockwise, 02å¡15'38". All distances shown/recited are grid and to get surface distances, divide the distances shown/recited by 0.9999785.
It's very similar to others on here.
Kris Morgan, post: 416649, member: 29 wrote: In Texas, you need only reference the system. Mine goes a little something like this:
BEARINGS are based on the Texas Coordinate System of 1983, Texas Central Zone per GPS observations. All coordinates are U.S. Survey Feet, NAD83(2011)Epoch 2010.0000 per static GPS observations and an OPUS solution through the NGS website. To get geodetic bearings, rotate the bearings shown/recited hereon, clockwise, 02å¡15'38". All distances shown/recited are grid and to get surface distances, divide the distances shown/recited by 0.9999785.It's very similar to others on here.
Are you reporting state plane distances on boundary surveys?
You can't rotate a state plane drawing to get geodetic bearings. A line of constant state plane bearing has a constantly changing geodetic bearing.
aliquot, post: 416672, member: 2486 wrote: Are you reporting state plane distances on boundary surveys?
You can't rotate a state plane drawing to get geodetic bearings. A line of constant state plane bearing has a constantly changing geodetic bearing.
Technically very true. Many surveyors still don't quite understand the mechanics of projections though, so Kris's simplified statement helps them to understand how to get from State Plane (which has a pretty large mapping angle in our part of the State) to "True North" bearings.
Some places i work only require a line between 2 monuments to be labeled as the BOB. Others require a narrative explaining how i determined bearings and the reference frame or record document held. I only list the equipment used when required. My preference is to be on State Plane Grid and I use the line referenced in the documents creating title. A sound basis of bearing is part of the footsteps.
aliquot, post: 416672, member: 2486 wrote: Are you reporting state plane distances on boundary surveys?
You can't rotate a state plane drawing to get geodetic bearings. A line of constant state plane bearing has a constantly changing geodetic bearing.
You're technically correct. Pragmatically, across 20 acres, it works. When it gets larger than that, I give the Angle of Convergence and CSF at my beginning point. That's how I handle it.
It should be noted here that while Shawn's method and mine "seem" to be different, both of us give the necessary meta-data to work from one to the other seamlessly and I've had ZERO problem taking ONE of his corners and being able to calculate and hit the others VERY well.
He and I had a conversation about this. His stance was that we measure on the ground so he is True and surface and gives SPC for verification and a tie to his LDP. Mine is simply on the grid.
The three things people get worried about are "How different are the distances from grid", "How much are the bearings different from true/record", and "How much different is the grid acreage from surface acreage". I have found that with regard to the first and last ones, with CSF on a magnitude of 0.9999 or larger, the acreage is different in the third and sometimes fourth decimal place, I only report to two decimals so no change there and the distances differ, depending on the length of the line, no more than a tenth and I typically fighting worse than that from the record instruments. With regard to the second item, I find that if I hold to the "OLD MTS" which stated that all material discrepancies shall be shown, and I show all of the record calls on both sides of the line I'm showing, the average person can literally see the difference. Whether or not they know what to do with it is up for grabs, but the average surveyor should be able to figure it out.
I love being on the grid for all projects be it acreage or lot jobs. The R10 makes it so easy to connect and having those corners, in other files, across the street, down the block, two tracts over, makes measuring those lines and seeing the conflicts (if any) SO much easier. It adds a ton of value and synergy to the product we can give out. Shawn has the same ability with his method and does the same things. We just report it different.
I'd follow Shawn any day (and have). 🙂
Kris Morgan, post: 416685, member: 29 wrote: It should be noted here that while Shawn's method and mine "seem" to be different, both of us give the necessary meta-data to work from one to the other seamlessly and I've had ZERO problem taking ONE of his corners and being able to calculate and hit the others VERY well.
He and I had a conversation about this. His stance was that we measure on the ground so he is True and surface and gives SPC for verification and a tie to his LDP. Mine is simply on the grid.
The three things people get worried about are "How different are the distances from grid", "How much are the bearings different from true/record", and "How much different is the grid acreage from surface acreage". I have found that with regard to the first and last ones, with CSF on a magnitude of 0.9999 or larger, the acreage is different in the third and sometimes fourth decimal place, I only report to two decimals so no change there and the distances differ, depending on the length of the line, no more than a tenth and I typically fighting worse than that from the record instruments. With regard to the second item, I find that if I hold to the "OLD MTS" which stated that all material discrepancies shall be shown, and I show all of the record calls on both sides of the line I'm showing, the average person can literally see the difference. Whether or not they know what to do with it is up for grabs, but the average surveyor should be able to figure it out.
I love being on the grid for all projects be it acreage or lot jobs. The R10 makes it so easy to connect and having those corners, in other files, across the street, down the block, two tracts over, makes measuring those lines and seeing the conflicts (if any) SO much easier. It adds a ton of value and synergy to the product we can give out. Shawn has the same ability with his method and does the same things. We just report it different.
I'd follow Shawn any day (and have). 🙂
Right on Kris. The important thing is clearly stating the metadata. We've modified things a bit over the years. I used to state that bearings were derived from Static GPS and that coordinates were determined from OPUS, but I've pared that down a bit. Partly because I feel more comfortable with the geodesy and partly because I believe surveyors in our area have collectively become more knowledgeable.
Kris, I feel the same way about y'all as well.
aliquot, post: 416672, member: 2486 wrote: Are you reporting state plane distances on boundary surveys?
You can't rotate a state plane drawing to get geodetic bearings. A line of constant state plane bearing has a constantly changing geodetic bearing.
Yes, it's not all that great an idea to apply one rotation to create "geodetish" bearings, bearings that resemble geodetic but that actually are geodetic on exactly one line. Geodetic North in Texas is generally a fairly useless commodity since nearly all of the state was originally surveyed by compasses and most later surveys referenced to astronomic North were really oriented in relation to it at one particular station.
If one is retracing a survey supposedly oriented to astronomic North, best practice is to recite the equation between grid North and astro North at points on the maximum East-West extents of survey to demonstrate the relationship, but report grid bearings since they are much more useful.
The post by Kris highlights an important sidebar.
The effects of the various projections in use vary dramatically by geography and time. Its not enough to know how things work in your primary area. If you dont understand whats going on behind the curtain, eventually something very bad will happen.
For boundary surveys I will give the data for the point of beginning, as others do. For easements and right-of-ways, I give the data for the control since we are usually running across several sections.
Bearings, distances and coordinates shown hereon are grid based on the "Texas Coordinate System of 1983, Central Zone" as determined by GPS Observations referenced to TGS Control Point "Winnebago1" (N:10609753.94 E: 1156789.92) where the convergence angle is -01å¡53'18.4 and the combined scale factor is 0.9991234. Elevations are NAVD88 (Geoid 12B)
I don't necessarily address the OPUS solution, but I might consider adding it. Again, for a subdivision plat or a boundary retracement, I would use a slightly different note, but the one above addresses the client's needs.
Either the survey is "true north" or a grid, if it's "true north" it's highly unusual unless you are a BLM surveyor,,, if it's grid then define it, either a SPC, UTM, LDP, record between know points, the choices are infinite, GPS is an aside to the process.
MightyMoe, post: 416712, member: 700 wrote: Either the survey is "true north" or a grid, if it's "true north" it's highly unusual unless you are a BLM surveyor,,, if it's grid then define it, either a SPC, UTM, LDP, record between know points, the choices are infinite, GPS is an aside to the process.
I suppose it could also be magnetic.
MightyMoe, post: 416712, member: 700 wrote: Either the survey is "true north" or a grid, if it's "true north" it's highly unusual unless you are a BLM surveyor,,, if it's grid then define it, either a SPC, UTM, LDP, record between know points, the choices are infinite, GPS is an aside to the process.
The mention of how grid or geodetic North was derived is important in that it should provide some idea as to systematic errors that may be present. For example, you could adjust a compass with the declination angle that would indicate grid North in a particular projection, but that would not be of the same uncertainty as grid North derived by other means. As a rule, GPS vectors provide the gold standard of orientation in large networks, with grid from near-geodetic from astro observations second, lines between classical triangulation stations third, and everything else falling further down the list. If a map only states that the bearing basis is grid North of a certain projection, it leaves open the question of accuracy which best practice would not.
Naturally, even better practice is to make some explicit statement about the accuracy of the coordinates from which the inverse computations were made that produced the bearings and distances on the map or description, but, failing that, some description of methods isn't useless.
Andy Nold, post: 416704, member: 7 wrote: For boundary surveys I will give the data for the point of beginning, as others do. For easements and right-of-ways, I give the data for the control since we are usually running across several sections.
Bearings, distances and coordinates shown hereon are grid based on the "Texas Coordinate System of 1983, Central Zone" as determined by GPS Observations referenced to TGS Control Point "Winnebago1" (N:10609753.94 E: 1156789.92) where the convergence angle is -01å¡53'18.4 and the combined scale factor is 0.9991234. Elevations are NAVD88 (Geoid 12B)
I don't necessarily address the OPUS solution, but I might consider adding it. Again, for a subdivision plat or a boundary retracement, I would use a slightly different note, but the one above addresses the client's needs.
When I'm doing route surveys and easements, I give the gamma/theata and CSF at the beginning point and grid coordinates where I enter and exit the property, maybe more depending on how many angle points it has in it. All of it state how the coordinates were determined.
I do for two reasons. One is odds are I'm fighting the boundary along the way and having the theata on the tract being surveyed allows me to quickly see how close the bearings are to true. The second one is that if you pick up on my survey, it's tie is to the tract with coordinates and not a monument distant from the tract. I'm not saying you're wrong at all, but that we're different.
