Which items do you hold when you see this. It looks like everything was computed?
You can solve a curve with just two knowns.
So solve the curve using different pairs from the table to see what makes sense.
That is why it is better to put a little extra info in the curve table.
> Which items do you hold when you see this. It looks like everything was computed?
I would expect some round off errors, you need to do some calcs to see if there are any significant conflicts.
That looks like a staking table to me... I would guess that it was intend to be laid out with curve points on the short chords. Never seen a record map like that, is it a construction drawing?
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> I would expect some round off errors, you need to do some calcs to see if there are any significant conflicts.
>
> That looks like a staking table to me... I would guess that it was intend to be laid out with curve points on the short chords. Never seen a record map like that, is it a construction drawing?
The curve table is actually from a recorded plat from the mid 1940's. Depending on what you hold, you get up to .40' error on other parts, like arc L, and radius. There is no real consistancy.
I like the direction (i.e. right or left), radius, arc length, delta angle, and long chord (bearing and distance).
Here's the approach I'd use (but I'm not LS)
You use the table to try to find the pipes, and if they are there, you hold them.
If there are no pipes or other good evidence, you lay out the total "Main" chord length and "Central" delta angle and see if it can be made to work. There may be a mismatch between the table's total chord and the lines it was supposed to connect, and you'll have to adjust accordingly. Did you find a significant discrepancy with the angles in the table that I overlooked?
Then you use the small chords to fill in. The only discrepancy I noticed in the table is that the small chords won't precisely fit to reach from the beginning and end of the total curve's chord. Then you have to decide whether to lay it out from one end, the other end, or maybe both ends and split the difference.
like said above, find some of the old mons, and work off it.
But, hold the Radius, and then the delta for calcs.
After you find some control, then just hold the radius.
N
Really?
How do you do it when you only have the arc length and the chord length?
i'm with nate on this one. as i was taught(in design stages), the tangents were drawn and computed first. the radii were set in and computed, thus deltas can be derived.
i was told to compute by delta and radius, whenever possible, as this was how the formulas were derived. i have heard of court cases in ROW retracements get ugly. one surveyor was badly discredited by opposition's atty because the baseline stationing didn't match the plat. i think i remember hearing that he may have used a chord (and that was the likely cause of the discrepancy)
Intersect the tangents to locate PI's, compare angles with table. I would probably hold PI's and radius and see how it fits record and ground.
jud
I normally go with central angle and radius but in this case the radius looks calculated from the degree of curve desired so using that might be a better solution for finding where they would have staked it.
I think the crew would have run the tangents in from PI to PI then filled in the curves later. This would support using the central angle. I would think they would measure the tangent back to the PC then deflected around the curve. Maybe they could see the whole curve from the PC or they would have to move ahead to some point on the curve to see around the rest of it.
Don't believe this is a stakeout table, those would be found in the notebook or in the job file not the Final Plat.
jud
Really?
> How do you do it when you only have the arc length and the chord length?
What is it, you're trying to find?
It's weak geometry, but if that's all you have, then I would just work the equation backwards.
Long Chord=5729.578/R*.3(this equals the deflection per ft in minutes)*(ARC)L. Work that down to decimals of a degree and take the sin * 2R.
I know other people do it differently, and some might come up with slightly different answers, but that's basically how it's done.
Dugger
looks like you need to follow in the footsteps.
Generally, they would layout the tangent lines, then come back and fill in the curves. Sometimes with a tangent offset method, sometimes turning the deflection and measuring the chord.
I would generally come from 2 different directions, if I could, then prorate out the error both ways.
Good luck.
Radar
Since I generate the significant part of my revenue as an Engineer, I would have to say that since I can't compute this to at least eight decimal places, I can't solve it. (Tongue firmly planted in cheek)
Really?
Seldom is it when you don't have the tangent in and out, that provides the location of the PI which would be the key to compute the remainder of the curve. I use PI's most of the time to base all curve comps on. When I need to define a curve for an existing road without curve data, I start with the old plumb bob, look along the vertical string and locate the PI by intersection, measure the apparent tangent lengths and tie it all with an external measurement as a check. Without the bearings in and out of a curve I don't compute curves, I want circular curves to be tangent at the PC's and PT's, I and will make them so if others data does not and a non-tangent curve is not called for.
jud
I wouldn't say they were 'computed', probably before computers.
I wouldn't say they were 'calculated', probably before calculators.
I might say they were 'derived', from a table for curve data.
Angles to the 1/2 minute, distances to the nearest tenth of a foot.
Just my take, follow the footsteps and the monuments found.
Computed or Calculated used to and can still mean "found from numerical operations" whether that was done on paper, with a slide rule, with a Marchant mechanical machine, an HP pocket calculator, or with a desk computer. I don't see the problem with using the words.
Computer used to be a job title, also, for the person who spent most of his time doing such work.
If this was along a R/W I'd do my best to retrace the original locations of the pc & pt and let the radius & delta float, as long as they were somewhat close. Especially if it was large radii, or a large delta. Some places have minimum radii, depending on design speed, so that's a factor too.
At intersection returns I always try and maintain the radii. Sometimes that can be a real challenge, especially if you have to cross the streets to further verify things.
But none of that is etched in stone. As usual...it depends
On the first line the radius, deflection angle (half delta) and chord work well together. Using the 25' chord the deflection angle calculates as 52°38' which would round to 53' as given. I would favor using the overall curve data for control over the shorter partial chord definition given because of the larger effect of rounding errors on smaller pieces of the curve.
