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# Need help with description "tangent of curve"

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Hello, we need help on deciphering the description below. What is meant by "tangent of curve" in this case? As you can see on a map, there is a curve in the highway just north of this marker, then the roads straightens out. I am familiar with a line being tangent to a curve, but don't see how that applies here. Tangent of curve at what point? Any ideas?

Thanks

Ron

http://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=FK0453

FK0453'DESCRIBED BY COAST AND GEODETIC SURVEY 1934

FK0453'7.6 MI N FROM SAYRE.

FK0453'7.6 MILES NORTH OF CRIPRR STATION 0.1 MILE SOUTH OF TANGENT OF

FK0453'CURVE. 90 FEET NORTH OF HIGHWAY CURVE SIGN. 36 FEET EAST OF

FK0453'CENTERLINE OF U.S. HIGHWAY 283.

Hi Ron,

I will give you my ideas on this. They may or may not be right. I am sure others will be along with more educated information.

I would assume that in this case the tangent line would run along the north-south section of the road that is highway north of the mark's general location. I would start measuring the 0.1 mile measurement at the point where the road south starts to curve away from that straight north-south section. This would seem to put the mark approximately in line with the east-west line separating 2 fields north of the scaled coordinates.

OR....

Maybe the tangent line runs along the straight section of the SE-NW run of highway and the point to start measuring from is where the road starts to break right and northward from that straight NW-SE section of road.

Good luck,

Let us know what you find.

Edited by TillaMurphs

I like Tillamurphs second proposal. It is close to 7.6 miles from the railroad and matches the coordinates reasonably well.

I wouldn't get hung up on "south of", but would read that as "southerly along the road from". The old descriptions for marks along a railroad and sometimes a road tended to not be based on actual compass readings (which wouldn't be accurate when sitting on the rails) but rather the general directional trend of the RR/road. I've seen diagonal intersections that read "north of the railroad and east of the road."

Since 0.1 mile is rounded (and was probably eyeballed) there is a range of a few hundred feet to search. And I wouldn't expect the same highway sign to be there as was in 1934 - that would be a real antique. And standard distances for placement of warning signs may have changed.

So I'd start at the coordinates, check that I was roughly a tenth of a mile from the start of the curve, hope that the center line hadn't moved much as the road was repaved, and search quite a distance each way along the road. Only 36 ft from center line would be a dangerous place for a disk during reconstruction of the road, so I wish it and you the best of luck.

Hello, we need help on deciphering the description below. What is meant by "tangent of curve" in this case? As you can see on a map, there is a curve in the highway just north of this marker, then the roads straightens out. I am familiar with a line being tangent to a curve, but don't see how that applies here. Tangent of curve at what point? Any ideas?

Thanks

Ron

http://www.ngs.noaa....l?PidBox=FK0453

FK0453'DESCRIBED BY COAST AND GEODETIC SURVEY 1934

FK0453'7.6 MI N FROM SAYRE.

FK0453'7.6 MILES NORTH OF CRIPRR STATION 0.1 MILE SOUTH OF TANGENT OF

FK0453'CURVE. 90 FEET NORTH OF HIGHWAY CURVE SIGN. 36 FEET EAST OF

FK0453'CENTERLINE OF U.S. HIGHWAY 283.

I would start at the RR station (CRIPRR STATION) in Sayre and go 7.6 miles to the north. At that point I would pace 12 steps to the east from the center line of the road. If you do not immediately see the mark then look both N & S parallel to the road and see if there is an indication for the mark. You may need to use a metal detector if it has been covered up. If you have access to a topo map it may show where the mark is located. The distance from the tangent is only a secondary location indicator, with the primary being the distance from the RR station.

Good luck,

John

I don't have much to add except that the mark does not appear to be marked on either the 1989 or 2012 USGS topo maps (Berlin quadrangle) on http://store.usgs.gov/. The 15-minute Sayre topo map from 1960 shows two benchmarks north of the curve -- 2079 (presumably the elevation in feet) about a quarter-mile north of highway 6 and 2104 maybe a mile north of that.

2079 is shown on the east side of US-283 but the elevation doesn't tally, and it's much too far away, I think, to be the mark in question.

~ArtMan~

0.1 MILE SOUTH OF TANGENT OF CURVE; means it is 0.1 miles South of where the curve ends (or begins), not into the curve but on the straight line portion of the road. In sketch, 0.1 miles south of the PT on forward tangent.

T - Tangent of Curve

PC - Point of Curvature

PT - Point of Tangency

PI - Point of Intersection of Tangents

E - External, PI to C/L of curve @ midpoint of curve

Edited by Z15

I took a look at the area on Google Streets and there is still a curve sign, although it may not be in the same spot. I grabbed an image that intrigued me though. Take a look at this:

If that is the Benchmark, its a miracle it survived that close to a cultivated area. A great many do not.

Often times the location of the PC and PT are very difficult to discern in the field, unless so monumented. Over the years of resurfacing the pavement etc., the PC and PT location as it now appears in the field may have shifted from their true location as set out by the original plans. We (as DOT technicians) encountered this numerous times.

Edited by Z15

I wouldn't be at all surprised if it was just a piece of trash, but I was happy to find that a curve sign still existed and that it was about 1/10 of a mile from what I guessed to be the tangent of the curve. It would certainly be worth checking out.

Just a little story. Years ago (Circa 2000)I was out doing recon for a future GPS project and there was a 1st order BM in a location similar to this, although there was a residence nearby. I searched around and could to find the mark so I moved on to another 1 miles down the road, gave up on this one. Some time later (months) I and my PS happened drive by this location heading to another job site. I mentioned to him that I could not find this mark the last time I was by here. He glances around and then says, "I thought I caught a glimpse of a BM". So I stop, turn around and go back. All be darned, there is a 12-inch concrete post sticking 6-inches out of the ground right in the area I was looking. There is some what freshly disturbed ground around the mark in the otherwise grassy area. So I put my foot on the mark and it moves, it was only 1 ft long, 6-in in the ground and 6-in projecting. We surmised the property owner might have destroyed it landscaping and keep it. When he seen me looking around for it he decided to replant it. We called the NGS advisor and he had no record of any resets and instructed us to remove what left and take with us. Note, the mark was on Highway ROW.

Edited by Z15

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