TANGENT OR NON TANGENT?

[LS 4722]

Sometimes, non tangent curves are the order of the day to preserve the found monuments in a way that a retracing surveyor can rely on the map math and what is out in the field.

Sure, tangent curves are nice and smooth, but who says that we have to hold everything to a perfect math fit? We show angle points, right? Why not fit a non tangent curve between found monuments? Really, what is the difference?

Anyway, I have attached a PDF of a survey I completed yesterday. This is in an area of Pasadena that has zero control for the avenues shown on the map. The only records I had available, other than the record maps that were done between 1913 and 1916, was a tract map on the north side of Oak Knoll, a CR for part of that tract map (which I basically ignored) and a PM on the south side of Fairfield.

The problem with the tract map and CR was that only the north side of Oak Knoll was addressed, the PM only partially re established the south side of Fairfield.

anyway...feel free to comment, I probably have typos or some other boo boo on the map.

PS I found quite a few 'undocumented originals' doing the survey. Darth will enjoy that part

[land butcher]

Sometimes it just has to happen. If I can slide something a couple of hundredths, within field location tolerance, to make the curve tangent I will.

One city I worked in had destroyed all the CL mons in downtown but a lot of the original 2x2s property corners remained. Many times this resulted in a street narrower than the record 50 or 60 feet. Oh well.

[btaylor]

Basically on curved areas like yours, I do not see how one can hold monuments without breaking tangency. I do it all the time.

What I typically see from others is either calling things perfect of record, and in reality you go out and find them within 0.2' of record, or holding two points and spinning the record and calling the others off.

[RMLAND]

Finally a post about surveying and not all that other crap from those with way too much time on their hands.
Very timely too Paul as I just did a topo across the street for the PM you mentioned of which nothing set was found

[LS 4722]

I spoke with the crew that was just setting up yesterday for that topo. David was running the gun. Is this David?

Edit: No, you are not the guy I spoke with. Your PM is at FM-11 and the guy I spoke with was working the parcel directly south of my parcel. What a coincidence, I finish a survey and two different crews show up on the same street on the same day. GL with your survey, at least mine was cleared and comparatively level.

[rpost]

Good point. I often rack my brain as to how I can possibly hold monuments in their original location and keep the curve tangent.

I agree with Butcher. If the mons are a few hundredths off, call em good and keep it tangent. Although I never have field location error; the monuments were just set a bit off.

I also agree with Mr. Taylor. I am getting tired of finding new maps with curve monuments held and missing by a couple tenths.

I also agree with RMLAND, nice to see a surveying post. Break that curve and hold the monuments! Or better yet hold 2 and call the rest off....just kidding.

[bruce hall]

off, hold them, hold the field delta using the monuments and break the radius.

You have the chord and the delta. what's so magic about the radius? Instead of a 300 foot radius you might have a 300.2 or a 301.

Do you want to hold the monuments or the math? You decide.

[bruce hall]

helped had I looked at the RS before I posted. Good Luck with the compound curves. If they aren't tangent, that's just the way it is.

My previous post had to do with tangents on each side of the curve. That method works pretty good. Never used it on compound curves.

[E_Page]

You could do this a couple of different ways, and I think either is valid.

One is to do as you did, hold the center of the monument and certain pieces of the curve data, reporting nontangent curves. Since nothing is marked between the front lot monuments, I don't see that it would normally make much difference one way or the other whether you hold the radius or hold the delta.

The other way is to do a best fit of the curve between the tangents using the measured locations of the monuments along the curve as your data points. If all fall within the distance of a reasonable standard error to the resultant curve, then it's just as good a method as holding the center of the monuments for the right of way to pass precisely through.

It can become a little more difficult to make this method work when there are record compound curves as you have here, or where the monument positions don't yield a curve that places all of the monuments (except perhaps an outlier or two) within a reasonably expected standard error distance from the curve.

Where I was surveying several lots on the same street, I've used the best fit method to good effect and, taking the expected errors (combined of your survey and the survey by which the monuments were placed) into account, uses the found monuments to control the location of the curved right of way.

Some don't see the best fit method as actually holding the monuments as controlling. I see it as holding the monuments taking an standard error into account while trying to also hold to the intended continuous curve that the subdividing surveyor attempted to monument.

As a practical matter, that the monument is a few hundredths within or outside of the RW is an inconsequential matter to the lot owner. If they build a fence, it will be several times wider than that few hundredths anyway. Besides that, they'll probably end up moving the iron a couple tenths as they build the fence if they don't knock it out altogether.

The attached map shows one such survey I performed using the best fit method. As I recall, the irons I held as data points for the best fit were all less than 0.1' from the curve I mapped per my measurements. I didn't note the trivial distance from the center of the iron to the curve unless it was an outlier and not held.

Sorry for the quality of the scan, but El Dorado County had their resolution set pretty low on their scanner back then to keep scanned file sizes small.

[LS 4722]

That scan was not bad at all to me. It's also nice to see a survey where both sides of the RW were included with found monuments.

. I didn't note the trivial distance from the center of the iron to the curve unless it was an outlier and not held.

If you are referring to my found Day monument, FM-6, in relationship to FM-1 and FM-7, I did that because Day's caps do not have any identifying mark that shows where the 1916 measurement was made, so anywhere within the cap is golden as far as I am concerned.

I make my maps not for the benefit of the client but for the benefit of those that use my work in doing surveys in the area. An RS is not a design survey that has certain tolerances that need to be maintained, such as a curve normal to both entry and exit tangents, but it is one that is basically just a report of what monuments are out there and how do the monuments fit each other, made for surveyors really.

[E_Page]

Nope, wasn't referring to anything on your map, simply explaining mine. I thought that your notes explained what you found and what you did pretty well. The only suggestion I would make would be to add the record data for comparison to measured. I know it can clutter things up a bit, but I think it's very good info to show.

[LS 4722]

I didn't note the trivial distance from the center of the iron to the curve unless it was an outlier and not held.

Ok, I see where you are coming from.

I have an example like that on my map. FM-14 notes that. Neither point would fall on the lot line (hold one, lie about the other or call it off) so I just meaned the line and noted it.

If the line passes through a pipe or tag, but not centered on the pin point nail so many hold dear, the pipe/tag is on the line.

I was able to use all the monuments I found in this survey. There was a CR filed across the street, which I basically ignored. When I see a RS/CR that reports pure record for both line/distance I know that just is not so.

I think I will stay with not placing record values on my surveys. Sometimes I do, most times I do not. Depends actually.

[Semper Fi 713]

I am currently a volunteer for the CLSA – San Diego Chapter LS Review Program. This topic “Horizontal Curves... Re-establishment Methodsâ€￾ seems to come up every year. I personally prefer to hold the original monuments, measure the chord and proportion between the found original’s (or perpetuations of original monuments). I also prefer to show the record and measured info on my map so that others in the land surveying community can better follow what I did on my survey.

I learned this method from Robert Lee McComb - LS 4441 in the 1990’s when Lee taught our LS Review Boundary Class. One of Lee’s Handout’s was a paper that had some Very Good Stuff on Re-establishing Horizontal Curves. Attached is some of that material with some of my notes.

See Problem # 6 via this Web Link for the Caltrans LS/LSIT Video Exam Preparation Course by Robert Lee McComb –PLS. Lee demos the Chord Method with (2) solutions; One holding the Record Delta Angle and the other holding the Record Radius.
http://www.dot.ca.gov/hq/row/landsurvey ... ook/13.pdf


Thanks,
Semper Fi 713
Jack Gechter-PLS

[PathFinder]

Thanks Jack - Excellent information!

[Civil Engineer]

1) Tangent curves are "special" because they are typically what was intended. Intent is the difference.

2) The multiple non-tangent compound curve solution is a "perfect math fit" of the measurements.

3) The primary purpose of the ROS is to show "measurement", and how that fits the existing.

Road R/W determination has been some of the most challenging work I have encountered in my career and has been the most interesting. The other posters already provided excellent posts, and given that each survey is unique and thought intensive, I don't have anything new to add.

[E_Page]

The purpose of an RS is to show the evidence found and the surveyor's professional opinion of how it pertains to the boundary location.

When performing a resurvey, it may be that the original surveyor intended to lay out a tangent curve but actually laid out points in the ground which cannot be reconciled to a curve that is tangent to the lines at both ends. In a resurvey, the surveyor's only authority is to identify the boundary as it was originally established on the ground. If it was actually established such that the points in the ground cannot subscribe a tangent curve, then the boundary (or RW) does not actually contain a tangent curve, regardless of what the map or deed may say. It is important to bear in mind that the right of way and the road are related but different types of entities. When making improvements to a road, if the existing road does not conform to the original plan, it is acceptable to remake the road so that it conforms to the originally intended alignment. If the right of way is found to not conform to the original map, it is not acceptable to remake it to conform with the originally intended alignment as a matter of resurvey.

Measurements are merely the means by which we report the spatial relationships of the evidence we've found. The use and significance of the various pieces of evidence are the most important aspects and primary purposes of the RS.

[LS_8750]

Thank you Mr. Page.
Radius, tangents, and arc lengths do not matter, road widths as well. Roads are bound by the monuments set.
Somewhere I heard an interesting term, "monuments control".

Of course unless the monument is the road, having no other evidence to draw from.