GPS Derived Basis of Bearing Plat Statement

I think your basis is grid not geodetic. Are the bearings converging? If not, then they are grid bearings with the origin point at that base point. And probably some type of projection going on in the DC. But without looking at it....I can't say for sure.

"..THE BASIS OF BEARINGS WERE DERIVED FROM GPS OBSERVATIONS ON THIS POINT AND ARE GEODETIC. DISTANCES SHOWN AS MEASURED HAVE BEEN REDUCED TO HORIZONTAL FIELD DISTANCES WITH A SCALE FACTOR OF 1."

You know the lightbulb, for some, will take an hour or so to warm up. I'm reminded of a time when a chief I was working for was told to set missing corners on a survey, done by another crew with rtk. He told registered he didn't want "the rtk points, he wanted the coordinates with a scale factor of 1" so we could use the robot.
Registered complied and handed him the coordinate list with a scale factor of 1. Quite the hairlip fit was thrown when "nothing was checking better than 0.20', and sometimes 0.40' "

I agree with Mighty Moe. I think you've got Grid bearings (geodetic at the meridian passing through the base point). I also wonder why the need to explain how North was derived. You probably don't explain in conventional surveys how the total station determined distances or directions. I used to state bearings determined by static GPS, but really this is immaterial to where North is on my survey. Having criticized you enough I will say that your statement passes the most important task of giving me enough information to reproduce your survey.

I think you could probably be ok stating that the bearing is related to a local grid with an origin of [base station lat/long]. Distances are horizontal at an ellipsoid height of [base station ellipsoid height]. I know you are in Alaska where heights can vary considerably which is why I mention heights. Where I am heights don't vary much so I just say horizontal distance at the surface of the Earth.

> THIS SURVEY WAS CONDUCTED USING SURVEY GRADE (MAKE/MODEL) RECIEVERS
> IN REAL TIME KINEMATIC MODE ON A LOCAL COORDINATES SYSTEM USING 'SOFTWARE'
> (V. X.X.X) RUNNING ON A (TYPE) CONTROLLER. THE BASE RECEIVER WAS LOCATED ON THE
> CONTROL POINT IDENTIFIED AS THE ‘BASIS OF COORDINATES’ WITH THE BASE DATA POST
> PROCESSED USING THE NGS ‘OPUS’ UTILITY. THE BASIS OF BEARINGS WERE DERIVED FROM GPS OBSERVATIONS ON THIS POINT AND ARE GEODETIC. DISTANCES SHOWN AS MEASURED HAVE BEEN REDUCED TO HORIZONTAL FIELD DISTANCES WITH A SCALE FACTOR OF 1.

M'kay. So you figured out what the latitude and longitude of the position where your RTK base was set up was +/- 5 ft. in longitude and you want posterity to know that, by god, that is where the "North" direction refers to?

Fine. Just note:

"BEARINGS OF LINES REFER TO GEODETIC NORTH AT LONGITUDE ___ NAD83. DISTANCES ARE ROUGHLY WHAT A SURVEYOR MIGHT MEASURE AT THE SURFACE OF THE LAND +/- 100 PPM, BUT YOUR MILEAGE MAY VARY BECAUSE ... RTK, DUDES!"

You and Shawn both nailed it. Thanks.

Well, I'm guessing with a bit of knowledge watching this stuff over the years. To further guess, I would think your distances are being calculated along the ellipsoid. I've seen that before. To get coordinates the controller has to project somehow. It's always best to KNOW how it's doing that. Some think that just because they assign small numbers to coordinates that they are surveying on a special little local system, but not really.....

Not sure why you feel it necessary to nominate what gear and software was used.

To my mind you only write down the info that is useful to others.

I don't. DNR asks for it. These are typically ROS surveys for easements crossing State land.
The OPUS position aids in they're getting the data into their GIS status plats. There's typically no fee conveyance involved, but control I recover has often not been seen in a hundred years. I'd like my surveys to be as useful as possible in another hundred years.

Kent. You probably need to spend more time painting. Good therapy for you, Dude.

"I" Before "E" Except After "C"

Your first spelling of receivers is wrong.

One cannot convert your ground information (map) to grid without some information on the elevation.

I don't care what kind of receiver or software you used, especially if you had some settings wrong.

As a minimum it is necessary to describe two intervisible points on the ground. Since you are giving Geodetic positions it is then necessary to give the bearing from A to B and from B to A. (Hint, in Geodesy they are not the same.)

Given the above, I may have sufficient information to possibly correct an error on your part.

Pi R square, cake are round.

Paul in PA

If you are on a Network, the system is already on grid which is a scale of 1 on the network. If you want to pull the trustee total station out, you would have to apply the combined scale factor of the job location to get something to work with.

My solution would be this. Place two control monuments in the center of the project. Cook the GPS off on both points. While shooting the points, watch the PDOP and the hrms (not the the average hrms). Remember, just because you have a great shot average doesn't mean you have a great shot graround us once you get the Grid location, pick the point you want to hold and get the combined annotating. Take that scale factor and use it in whatever collector you use and physically check it with total station. Then check couple more points around the project. If everything checks, then you can use the central point on your Plat and annotating that on your plat. Now, anyone with a GPS can put those two points in apply the scale factor to get to ground from grid and go to work.

Latitude will also be important in a local grid because this affects the rate of change in convergence east and west of the central meridian.

> Latitude will also be important in a local grid because this affects the rate of change in convergence east and west of the central meridian.

As long as the position of the RTK base was somewhere within 15 miles of the rover, the latitude on the meridian of longitude of the base where the survey grid was oriented geodetic North shouldn't matter when bearings are expressed to the nearest second of arc.

> The OPUS position aids in they're getting the data into their GIS status plats. There's typically no fee conveyance involved, but control I recover has often not been seen in a hundred years. I'd like my surveys to be as useful as possible in another hundred years.

So, why don't you put your surveys on a *standard* projection? That seems like a classic no-brainer case for it. The GIS folks would get it right without breaking a sweat and your posterity will thank you for having done a professional job instead of some run-on bearing basis note telling them how you pressed F2 while holding down the ESC key on an Oster Stake-a-matic Data Collector to determine the Northish direction of the lines you reported.

> > The OPUS position aids in they're getting the data into their GIS status plats. There's typically no fee conveyance involved, but control I recover has often not been seen in a hundred years. I'd like my surveys to be as useful as possible in another hundred years.
>
> So, why don't you put your surveys on a *standard* projection? That seems like a classic no-brainer case for it. The GIS folks would get it right without breaking a sweat and your posterity will thank you for having done a professional job instead of some run-on bearing basis note telling them how you pressed F2 while holding down the ESC key on an Oster Stake-a-matic Data Collector to determine the Northish direction of the lines you reported.

Wow Kent.

I'll try my best to extract some useful information from your otherwise sarcasm laced diatribe.

Larger projects are done in a standard projection, routinely.

The question of this note came about in my mind for small jobs in the past I'd done conventionally and rotated the work to a record bearing between two monuments of record. With a small RTK survey, rather than rotate the work out of the reference frame established by the location of the base, I'm considering leaving the survey in the original bearings and reporting the measured distance and bearing between the same two monuments, but not rotating. Just reporting.

The primary reason I don't work in a projection while doing some field work is straightforward. The original GLO and BLM surveys that everything else was built off of here were originally done using astronomic bearings. Ninety-five percent of the surveys I'm working with are on these bearings. When I'm computing search coordinates in the field on my 'Oster Stake-a-matic Data Collector', if I'm working in a projection that is applying a mapping angle and scale factor, those record bearings and distances done in 1915 are much more difficult to relate to and subsequently know where to look for evidence. If my base is located in the same general area, I've found the GPS 'Northish direction' bearings mirror the old astronomic bearings extremely well, leading me to search in the correct location for the evidence. I guess the whole concept of 'walking in the footsteps of the surveyor' before you has now been replaced with 'if you're not using Star Net and a standard projection, you're a hack'.

I'm sorry I'm probably not half the surveyor you are Kent. I probably never will be. But I will continue to strive to improve upon my weaknesses and there will always be arrogant blow-hards, and I just have to remember that they to have something to teach me.

I'll study this thread over to extract what useful information I can and disregard the rest.

Cheers! Carry on.

"I" Before "E" Except After "C"

Forward, back and mean bearings. You're suggesting I provide such on a survey covering 5-10 acres. Got it.

Thanks for spelling and grammar lesson. It's been a long and grinding week and apparently I didn't get enough punishment so I needed to come here.

Thank you for delivering.

"I" Before "E" Except After "C"

"I" Before "E" Except After "C"

> Thank you for delivering.

Some folks are a prime example of why one-man crews were invented! :pinch:

> The primary reason I don't work in a projection while doing some field work is straightforward. The original GLO and BLM surveys that everything else was built off of here were originally done using astronomic bearings. Ninety-five percent of the surveys I'm working with are on these bearings. When I'm computing search coordinates in the field on my 'Oster Stake-a-matic Data Collector', if I'm working in a projection that is applying a mapping angle and scale factor, those record bearings and distances done in 1915 are much more difficult to relate to and subsequently know where to look for evidence.

Does that sound right to you when all it would take is to draw up the original GLO and BLM surveys and *rotate* and *scale* them to grid to get as accurate search coordinates as you do using some North-ish direction somewhere in the vicinity where an RTK base was set?

Have you asked the GIS folks whether they'd prefer LLH or Alaska State Plane Coordinates for your work as reported?