California Surveyors Forums

The new Corner Record form has a space for entering CCS coordinates.
http://www.pels.ca.gov/pubs/forms/corner_record.pdf
How would you use (submit) this information?
Would this only be used to replace a point that already had CCS values?
Would you use this to place approximate CCS values on a replacement (8771(b)) BM?
Would you place OPUS or OPUS-RS values on a monument?

8771.5. Record of survey - California coordinates
When coordinates in the California Coordinate System are shown for points on a record of survey map the map may not be recorded unless it also shows, or is accompanied by a map showing, the control scheme through which the coordinates were determined from points of known coordinates.

Could be a busy CR if the same applies (or why wouldn't it?)... What are your thoughts, oh, experts of Land Surveying???

Thanks, Rob

was trying to incite a little conversation and opinion sharing here... As Dave pointed out, the PRC is the source for the info - Specifically 8813.1. through 8816 for this question... (www.leginfo.ca.gov search in Laws for 8801 and check PRC)

Lots of info to include on a CR... Probably not impossible...

8813.1 After December 31, 2005, any survey that uses or establishes a CCS83 value or values shall meet all of the following requirements:
(a) The survey shall be referenced to and shall have field-observed statistically independent connections to one or more horizontal reference stations... 1,2,3ABC,4ABC
(b) If an accuracy is to be claimed for the CCS83 value or values established, the claimed accuracy shall be an accuracy standard published by FGDC or FGCS.

8813.2. After December 31, 2005, if an accuracy is claimed for a CCS83 value or values, the survey that established the value or values shall be documented on a map, record of survey, corner record, or other document that includes, in addition to other requirements in this chapter, the following:a,b,c

8813.3. (a) After December 31, 2005, when a survey that uses or establishes a CCS83 value or values is shown on any document, the station or stations to which the CCS83 value or values are referenced and connected and the CCS83 value or values and the published or stated accuracy or accuracies of that reference station or stations shall be shown also on the document.

8814. State plane coordinates may be used for property identification on any map, survey, conveyance, or other instrument which delineates or affects the title to real property or which delineates, describes, or refers to the property, or any part thereof. However, to constitute, when recorded, constructive notice thereof under the recording laws, the delineating, describing, or referring to the property, or part thereof, shall also refer to data appearing of record in any office, the records of which constitute
constructive notice under the recording laws. That record data shall be sufficient to identify the property without recourse to those coordinates, and in case of conflict between them, the references to that recorded data shall be controlling for the purpose of determining constructive notice under the recording laws.

8815. The use of the term "California Coordinate System" on any map or document or in any field notes shall be suffixed either with "27" (shown as "CCS27") for coordinates based on NAD27 or with "83" (shown as "CCS83") for coordinates based on NAD83.

8815.1. When CCS83 coordinates are shown on any map, corner record, or other document, the map, corner record, or document shall state the epoch (date), in a decimal year format to two decimal places, that is the basis of the coordinate values shown. The epoch shall be shown on the map, corner record, or other document by an appropriate note on the map, corner record, or document or by adding a suffix in parentheses after CCS83 that states the epoch; examples, "CCS83 (1991.35)," "CCS83 (2002.00)," and so forth.

8815.2. The epoch for a survey using CCS83 coordinate shall be the published NGS or CSRC epoch of a published coordinate for a controlling station used for that survey. Such surveys performed after December 31, 1999, shall be based on the "1991.35" epoch or a subsequent published NGS or CSRC epoch.

8815.3. When the published epochs of the controlling stations for a survey using CCS83 coordinates are not the same, appropriate adjustments shall be made to the horizontal positions of controlling stations so that the coordinates of all the controlling stations are consistent. These adjustments in the horizontal positions of controlling stations shall be made in accordance with procedures and values published by the NGS or CSRC.

8815.4. When a purported order of accuracy of second order or better is shown for CCS83 coordinate values on any map, corner record, or other document prior to January 1, 2006, that map, corner record, or other document shall use the order of accuracy as defined by the FGCS. If an FGCS order of accuracy is claimed for a survey or a map, it shall be justified by additional written data that shows equipment, procedures, closures, adjustments, and a control diagram.

8815.5. When CCS83 coordinates are shown on any map, corner record, or record of survey, a mapping angle, combined grid factor, and the elevation used to determine the combined grid factor shall be shown on the map, corner record, or record of survey for at least one representative point.

8816. The use of the State Plane Coordinates by any person, corporation, or governmental agency engaged in land surveying or mapping is optional.

Warning - FGCS standards may cause your head to explode...

I missed the part about using CCS on the form. where is it?

I would not use CCS values unless requested to do so by the client.
I would use CCS values and all that entails, if I were doing before and after CR's on control that had CCS values established on it already.
There maybe other reasons why I would use CCS, but generally would not use those values for property corner evidence.

I would not use a CCS value to help navigate to a replaced BM. I might use NAD83 state plane coordintes to help navigate to a BM. There will need to be the appropriate metadata whether using CCS or NAD83 state plane coordinates.
I see no reason why in certain circumtances, OPUS or OPUS-RS could not be used along with appropriate metadata.

Because of PRC §8815.2 and §8815.3, I will not provide CCS values of any point of my survey. This requires that I use a linear function to "move" points back in time to a mathematically created position which, in non-linearly moving Southern California, is a false position.

These sections of the PRC do not account for the location of the 1st order stations or the location of the survey points or the location of any fault line which may lie between the control and the survey. It dioes not account for the spastic or plastic motion of the earth. The only thing that we know for sure is that the "calculated" position fort the points is highly liekly to have never been occupied by the points.

In short, these two paragraphs are inadvertently designed to produce false information.

Untill such time that I can report the CCS values based on the day's observation and the metadata for that observation, I'll keep my CCS values to myself.

I have not looked in while to see what epoch CSRC is on. What are there paramenters for updating epochs? Is it keyed of the most recent event? How much difference or distortion do you see introduced in the values of your true of date epoch v the pubished epoch. Are the continous stations you use to process on some slightly older epoch? Do you correct for this by bringing them to a ture of date epoch? If so does this introduce a significant disortion? I agree that the linear process adds wunwanted distortion, but whats a poor surveyor today? What about subsidence? Any models for that? Anyway to detect it and correct for it?

Ian thanks for your comments

Dane:

The first order stations can be on one side of a fault and the survey site on another. If the observations are made after a seismic event, using any of the "tools" to reduce the data back to a published epoch will absolutely create false results based on the magnitude of the event. The reported data will be useless.

The "tools" to reduce observed data to a published epoch do not take into account variations based on location. Even without a seismic event, the non-linear, non-regular movement of the earth's surface in Southern California will produce modified data that are flawed, inaccurate and based on a linear interpretation of a non-linear event.

In short, the consequence of the two sections of the PRC is that data reported, by definition, is flawed, inaccurate data reporting something that never existed.

That’s why, until the two sections of the PRC are “repaired” to allow proper reporting of observed data instead of mandatory reporting of flawed “adjustments” to my data, I will not provide SPC values for any points on my survey. A much better approach would be to report the observed data and the metadata concerning those observations.

Oh, by the way, read the Surveyor’s Statement required for a Final Map. If you report the SPC coordinates on a Tract Map, is your survey still “true and complete” or are you committing perjury?

Ian,

I completely agree with what you are saying. the subject is apparently something you have struggled with and given considerable thought and I wonder if you could respond to the other questions I asked. As far as the prejury comment, could you expand on that. I am not sure I followed what you are saying.

thanks for your help

Dane:

If you are signing a statement that said the survey you have performed and the map is “true and complete”, but you know the data your showing never existed and is flawed, that could be considered as committing perjury. Hmmm…

What are there parameters for updating epochs?
I do not know the answer to this question.

Is it keyed of the most recent event?
Not necessarily. I have seen significant, local events that have not triggered a new epoch.

How much difference or distortion do you see introduced in the values of your true of date epoch v the published epoch.
The shifts are dependant upon the time period between the observation and the published epoch. By “adjusting” our observed data “back through time” to a published epoch by using a linear mathematical equation, we KNOW we are introducing as element of error. The phenomenon for which we are attempting to mitigate is clearly non-linear!


Are the continuous stations you use to process on some slightly older epoch?
The CSRC provides both daily values and published epoch values for the CGPS Station.

Do you correct for this by bringing them to a true of date epoch?
I’m not sure what you’re asking, here.

If so does this introduce a significant distortion?
By definition, it produces a distortion, the magnitude and direction of which we will never know.

I agree that the linear process adds unwanted distortion, but what’s a poor surveyor today?
Well, my response is to refuse to issue my data with SPC values until the PRC is changed to allow me to report what I observed and the metadata defining the observations.

What about subsidence? Any models for that? Anyway to detect it and correct for it?
What about it? No. and No.

"That’s why, until the two sections of the PRC are 'repaired' to allow proper reporting of observed data instead of mandatory reporting of flawed “adjustmentsâ€￾ to my data, I will not provide SPC values for any points on my survey. A much better approach would be to report the observed data and the metadata concerning those observations."

I rarely publish coordinates on a filed map -- it's generally not worth the trouble. However, I'm not sure what you mean by the above, Ian. Can you elaborate?

Jim:

When I perform a boundary survey, I occupy points and run fast static sessions. I bring all the data back to the office to process the files. Being in Southern California, I am fortunate enough to find myself in the midst of a plethora of CGPS Stations of which I can download the daily observation files.

I process my observation files with those of the CGPS Stations. Once I’m happy with what I’m looking at, I “fix” the control based on the daily positioning for each CGPS Station that I intend to use to fix my survey site. In this manner, I develop SPC values for my site based on the day’s observations, fixed to 1st Order CGPS Stations.

If I have to provide my results in SPC, by statute, I must take these daily values and run them through the utility that “moves” the points back in time to the values based on the last published epoch (or the published epoch being required by the project). It is this enormous damage of unknown magnitude that I object to. It is my experience that the crustal motion in our area is not linear and does not occur in a uniform manner over an area of any size. The modeling does not take this into account nor do any of the models attempt to deal with localized, minor earth movement from low magnitude seismic events that are a daily occurrence in our part of the world.

The result of all this is that I am not comfortable providing knowingly corrupted data and refuse to do so. In the end, I fix my boundary and then rotate the work onto two fixed points that are monumented with found monuments from a single, record map. This is exactly what we used to do with boundary surveys done by total stations and traverses. The community looses any potentially valuable SPC results from my work, because, in my opinion, the statutes are seriously flawed.

What I would like to see is the ability to publish the results of my adjusted survey based on that day’s observations from my field occupations and the daily CGPS Station files. I would be very happy to provide the observation data as well as the positional data for all the points in the control scheme and the relative positional tolerance for each point. With this information, any future user would be able to decide for themselves the value of the work. They would also be able to use what will obviously become more refined tools to manipulate the data through time in a manner more in keeping with reality than forced errors and corruption. But, alas, the current state of our laws prevents this.

I realize that, in many cases, the differences are quite small. However, without significantly more work and data, we have no real idea of those differences. Further, since we know that we are corrupting the data by conforming to current statutes, should we allow our work and data to be published knowing that it is in error and that we have no idea of the magnitude of that error?

If we were all living somewhere such as Lawton, OK, where the crustal movement is virtually uniform for hundreds of miles in every direction, I wouldn’t be writing this. However, we do not. The place where we do live and perform our work is in constant motion that is not uniform, linear or capable of being modeled to any extent over relative ly small areas that comprise those ofmy surveys, even including the areas bounded by the CGPS Stations I choose. Unfortunately, our current statutes simply do not account for this. Until they do, I will not provide SPC values for my work.

Now, Rob, see what you’ve done with your wimple little question about SPC values on a Corner Record?

Enjoy the weekend, all!

And, to my friends in Roseville (and you KNOW who you are!), I had a great time with you guys and look forward to spending more time with y’all.

"Unfortunately, our current statutes simply do not account for this. Until they do, I will not provide SPC values for my work."

I rarely publish CCS values on filed maps because it's generally not worth the trouble. However, I guess I take a more liberal interpretation of §8815.2 than some. It seems to me that the critical phrase in §8815.2 is "published NGS or CSRC epoch." To my way of thinking, the statute oversimplifies the technical issues, and since CSRC is pretty tightly integrated with SOPAC, I figure that SECTOR day-of-observation values meet the intent of the legislation. I feel the same about OPUS with a 4-hour or better session.

I process against the ITRF values to stay consistent with the precise ephemerides, then adjust to NAD83 values. I show ties as required to the control stations, and provide the day-of epoch. (The last time I did this I had to backdate the epoch from 2007.x to 1999.51 to meet contractual requirements, but I described the process in the ROS narrative.)

No complaints yet. :)

Jim: I understand your position and have thought of it many times. The definition of what a published epoch is one of the serious flaws of the legislation.

I've never had any complaints, either, even when I WAS publishing SPC values. I suspect that the lack of complaints was not because of the lack of flaws but the lack of understanding of what the data represented and the difficulties in bastardizing it into the format presented.

We have developed too much of a "Cult of the Box" when it comes to using GPS equipment and analyzing the results.

“All Hail The Box! The data is accurate to 16 decimal places because it cometh from The Box! Redundancy checks are not needed for the Box sayeth so. All Hail The Box!”

Ian "Box Heretic" Wilson

Ian

BIG LOL,

For corner records, I'm only filling that line in to the nearest second either from a GPS shot or from googling the address. I'm not sure what the creator of the form actually means or what they are looking for when they want that information disclosed. AND there are still a few folks out there not using GPS at all.

If I use the nearest second, then I'm only admitting 600 feet more or less.

May good PDOP be with you "o" Mighty one

McGee, where are you? I think that you should hold a seminar on this for these fine gentlemen. I know I would go!

The whole Horizontal Time Dependent Positioning (HDTP) is used where you have differing epochs for control monuments and you want them on the same epoch for comparison. Usually I hold one, and see how I check into the others as confirmation that I have not screwed it up somehow.

The Coordinates shown on a Corner Record is interesting however. Are you saying that if I show them, then I should show my control network? Can you input hand-held coordinates, or autonomous derived coordinates? Basically, they mean nothing to me as far as restoring the monuments unless someone took the time to show the control sketch. Maybe they are put there for convenience as in BLM monuments out in the middle of nowhere that will help in locating the monument later?

Coordinates are being asked for now, On Flood Certs also. Maybe somebody saw this requirement on those and thought it would be cute to add it to a Corner Record.
Like Gromatici says, that info is sort of usless . . .at least more useless than the control and replacement schematic on the corner record plat itself.

Aren't these geographic locations shown on the plat in the form of section township and range ? or rancho ? etc. I guess we can take a rapid static OPUS shot then add the report to the corner record pkg.

Is this, or will this, be required for a Record of Survey ?

Gentlemen, Thanks for the thread this is a worthy discussion. In regard to 8815.2 and 8815.3 of the PRC, the intent and application is not understood here.

We normally work in some common datum which is usually NAD83 in California. NAD83 is actually fixed to the North American Plate east of the San Andreas Fault. A large part of California in moving with respect to the North American Plate, and because of GPS, we can measure and report this. We find it necessary in California to state the Epoch of regional re-surveys because they are referenced to the N. American Plate. However, local surveys that are referenced to (tied to) local monuments with NGS sanctioned NAD83 positions need to state the Epoch being used. This is important since other surveyors before or after may use the same monument but a different Epoch position. We should always reference our surveys to NGS sanctioned positions to give validity to the SPC's as required by the PRC and for uniformity.

Presently, the positions on the California CORS (called CGPS) are published on the 2007 Epoch which are NGS sanctioned positions published by the CSRC. This doesn't mean the previously NGS sanctioned 2004.0 Epoch positions on the CGPS or any sanctioned position on any "in the ground" monument are no longer valid. It does mean that, if you in the course of your survey, you find you have monuments on both epochs, you may use the tools available from the NGS or CSRC to move them to a common epoch. The error over a short time, notwithstanding earthquakes not included in the models, may be millimeters or several centimeters over longer periods. You can test the accuracy of the models against monuments with multiple epochs. Generally, over a local area, which can be large, everything is moving pretty much together so when surveys are constrained to (tied to) an older epoch position with GPS measurements taken today there is no problem.

I would avoid using daily solutions on CGPS because they are changing daily and you will end up with all of your surveys on slightly different epochs. Two survey a year apart will differ by about 3-4 centimeters depending on the region. After a few years the differences will be unacceptable. The purpose of the PRC is to require we publish SPC's on a sanctioned position/epoch and state that fact so other surveyors can retrace us. We do want to be retraceable don't we ?

In summary, the PRC is not requiring new measurements be distorted nor false positions be created but rather to insure that SPC's are published on an acceptable sanctioned epoch.

One added comment. I can see how the argument that "SECTOR day-of-observation values" and OPUS could satisfy the PRC requirement for an NGS Epoch; however, it is not the intent. The intent is to base surveys on a common published Epoch. As a matter of information, in other parts of the US, an Opus solution is consistent with prior published coordinates but not in Calif. Because we are moving at a velocity of 2-4 centimeters per year west of the fault lines. The problem with Opus is you have to use the HTDP program to put them on a published Epoch in Calif. If you do this, I would suggest that in the ground monuments be included in a survey to QAQC the combined OPUS and HTDP solutions. I prefer to download rinex files for the CGPS and compute positions for surveys based on the published/sanctioned 2007 Epoch of the CGPS.

Michael:

I must strenuously disagree with your assumption that we on the Pacific Plate are moving at a rate of 2-4 cm per year with respect to the North American Plate. This is a commonly reported claim that is patently false.

We, on the Pacific Plate are moving at an AVERAGE rate of 2-4 cm per year with respect to the North American Plate. However, that is an average that does NOT correspond to any small area over any fixed period of time. The movement, at a localized level, may well NOT be linear or steady, particularly after a seismic event, and such movement is certainly NOT regular. The application of any “shift” based on linear, regular movement, by definition, forces error into the data. It is this forced error that I object to.

As you stated, “…(t)wo survey(s) a year apart will differ by about 3-4 centimeters depending on the region…” This is exactly my point. The magnitude of those difference WILL vary from area to area due to differences in local seismic activity.

If you re-read the method I prefer to use, I use daily data files downloaded from the CGPS and process those against my observation files from my own receivers THAT WERE PLACED OVER FIXED POINTS. The control scheme used begins at one CGPS Station then proceeds to the first on-site fixed point followed by the second on-site fixed point and terminates at the final CGPS Station. As you note, this allows for future use of the data regardless of the ultimate position or configuration of our portion of the Pacific Plat/North American Plate collision area.

Most, if not all of my work is on sites less than 40 acres. The control points I had near Anza moved considerably during the summer of 2006 while my control points near Moreno Valley experienced no similar movement. In fact, it was this seismic event that helped me to realize the folly of reporting my data in the manner requested by the PRC. The differences in movement between my points near Anza and those near Moreno Valley are completely discounted by any method of reporting on a published epoch. Without being able to note those differences, what use is it to report my data in SPC values in the first place?

The PLS Act and the Subdivision Map Act both require me to state a Basis of Bearings for my surveys. Whether I use SPC values to establish that Basis of Bearings or merely reference the bearing between two found monuments with an arbitrary bearing is immaterial for regional survey work.

As you point out, “…the PRC is not requiring new measurements be distorted nor false positions be created…”, this is merely a by-product of the requirements.

For academic purposes, with the entire state of California as its palate, the methodology prescribed in the PRC is a valid tool. For local surveyors working, practicably, on small tracts of ground, even over the course of a number of years, those methods are simply not useful. The location of the boundary will remain a legal function and not a mathematical one.