For years I had a standard note on my plats that read:
"Bearings are based on angles turned and a single magnetic observation".
When I DID rotate to match a previous survey I did not add that note.?ÿ If I can find two or more monuments then I can "make it fit".?ÿ I worried a lot more about distances and monuments than bearings.
While I agree that the equipment and software today make it easy(ier) to match SPC I had always been taught that I was trying to "Walk in the steps" of the previous (if not original) surveyor and to produce a plat that can be retraced on the ground.
Andy
@bstrand it would be the numbers on another surveyors plat.
N
A sound Basis of Bearing will aid in the recovery of monuments.
We are currently working on a right-of-way staking project for the purpose of sidewalk construction. The north part of the project is platted, dated 1970, and the rest of the project is metes and bounds. I'm trying to calculate property corner positions, for the purpose of recovery, on my way down a right-of-way line from the plat to the terminus of the project. I want to hold the west plat bearing. I found the deeds for those metes and bounds properties. Some of the deeds have actual cardinal directions for the section lines. I noticed one section line bearing was at least a degree different from the plat bearing, which runs along the same north-south center of section line. I even calculated the bearing of that same line using the state plane coordinates of the S 1/4 and N 1/4 corners. That bearing was several degrees different from the plat bearing. I didn't apply a mapping angle to that calculation. I probably was supposed to do that, right? I was told that in theory, the interior section lines are straight. I assume the only exception to that would be if the center of section was set.
Do you think that holding the plat bearing is reasonable? What I'm thinking of doing is pre-calculating the right-of-way line using a local (N = 10,000, E = 10,000) coordinate system, locate 2 plat corners with RTK, then rotate and translate the local coordinate system to the grid. After that we'll use RTK to find the property corners. Does that make sense?
AMEN
As long as we are using, and continue to use monuments and evidence on the ground, the basis of bearing is basically irrelevant in finding the boundaries.
I agree with Brian's statement, but what about adjacent boundaries? Don't I have to relate my basis of bearing to find those boundaries?
I surveyed in in Nebraska from 1975 to 1990 and we didn't show or use bearings.
We measured angles and showed those on our surveys.
Why would you want to do all that math
We measured angles and showed those
It makes sense to show what you measured. If you are using a TS you are not measuring bearings.
@field-dog I would say sure, but that doesn't mean that the basis of bearing for one deed is better or worse than another. So, I am in a colonial state, no mandatory recording laws. I plot all the deeds for a boundary and rotate and translate then to fit together. I try and rotate everything to my deed bearing base, even if I don't know what it is. Sometimes they fit together well other times not. My survey might begin many different ways depending on what I am surveying,
For instance, a small tract or lot I would load the coordinates in the data collector from my deed plot, head out and start looking for corners. That's rough chaining around, pacing, looking at possession. Find a few and do a resection to get on the deed plot basis plus or minus. After I am done I may hold my deed bases for the survey, or an adjoinerd if I have better information on its origin. But really, I don't care too much. I make sure it not stupid, but am more concerned that the corners I found and held as well as what I staked-out are all marked up and property noted on my boundary plat for the client. My plat will always state where the bearing basis came from.
Large farm parcels or a job for a government agency might be entirely different.
It is always interesting here to see how others work in different locations s around the country.
1. Current measuring equipment provides greater positional accuracy than state plane coordinate systems are capable of reproducing.
Please explain your rational for this.
@bill93 What would I have to use in order to be justified in showing bearings on my plat? A better question is there anything that measures bearings? Or are they possibly always derived from something else actually being measured?
is there anything that measures bearings?
Magnetic compasses measure bearings, maybe corrected with an estimated declination (formerly called variation) to get close to astro or geodetic bearing. So most of the old surveys done with a compass did measure bearings, particularly for large Colonial parcels or PLSS sections. You could also measure angles, which was perhaps mostly done on smaller lots.
Gyro compasses also can be set up to measure bearings.
Everything else I can think of makes some other kind of measurement which can be converted to bearings. GNSS coordinate pairs can be used to calculate bearings, or TS angles to bearings by fixing one line's bearing.
Please explain your rational for this.
That comment was made 8 years ago, by a member who hasn't posted in the last 6 months, so I doubt that he will be here to defend that poorly worded comment. I'm guessing that he is referring to the fact that the SP system assumes that a 1 part in 10,000 scaling can be considered insignificant.
I don't really care much about the basis of bearing on drawings. We cogo them all up and rotate them to a section line within our state plane coordinate system database. Most of which is our own, but sometimes it's from the County we're working in. Then we create search points based on that and go about our business and start searching for mons. All our work is done on state plane(on ground), always.
We cogo them all up and rotate them to a section line within our state plane coordinate system database.
In other words, your basis of bearings is State Plane.
Back in the days of transits & optical theodolites, we didn't measure bearings, but rather azimuths. Set up a baseline, usually along a road, assume an azimuth from gun to BS, load that on the plate, point with lower motion, turn with upper motion to azimuth ahead. Move the instrument ahead, backsight with azimuth ahead ±180°, repeat. Angular error of closure readily apparent at end of traverse. I still have (somewhere) lat/dep traverse sheets for solving azimuth traverses.
Cheers! SS
