Modernization Of The Field

[+BuckBrooke]

Greetings. I've been in communication with the fellow in charge of the Surveying/Monumenting office for NM-DOT. In particular, his comments below reference two lines of PIDs, one of horizontal ADJUSTED stations from 1969 and one of vertical stations (SCALED horizontally) from 1982, that run along I-25 from Santa Fe to Socorro. His comments about the usefulness of an online state benchmark database and their use of monumented stations are below:

 

Most of the control monuments you have described were set during the 60's, 70's and early 80's using terrestrial survey methods and the accuracy/precision of the data is no longer considered useable by today's GPS standards. The use of the NAD 27 map projection is one of the main reasons for our abandonment of these old monuments. We do on occasion attempt to utilize some of the old control if the monument is stable and meets our rigid GPS monument standards. Also, the monument's location and vertical reference are also evaluated for possible use. We no longer consider control as a permanent feature given the relatively easy task of establishing quality control on our roadways. We basically bring in new control for any new project in a matter of days unlike previous decades where terrestrial control could take over a month of control surveying. Our control is now evolving in the direction of an almost disposable quality due to the high cost of maintaining current control networks. I believe with the migration to VRS systems, CORS stations, and OPUS processing services the old standard of preservation of control will have to be evaluated for long term cost.

...

Your suggestion of having the old records updated could possibly have some merit for the private sector that still rely on these monuments for rural boundary surveys

and GIS mapping.

 

I did not realize that there was a significant difference between the public and private sector surveying needs. I imagine it has to do with needed accuracy of surveying for different magnitudes of projects and the quality of equipment required? Do his comments reflect the general attitude in the field, or specifically that of DOT surveyors, who focus upon roadways?

 

Is there a move towards not creating new stations, and relying totally upon the ease of GPS?

Edited June 2, 2005 by BuckBrooke

[evenfall]

I think there are other ways I'd look at the big picture, Buck. Here are the easy reasons.

 

For the most part it is important to note that all politics are local.

 

This happens to be New Mexico's official take on it.

 

The Truth is you cannot do everything with GPS.

 

The Truth is that NGS Control is the grandfather control.

 

The Truth is that many agencies and municipalities have created their own control as well but it is based upon and accurized by NGS control.

 

The Truth is that though there are national, state, county and city networks, most all of it ties back to National. Further, a State employee may have rules that force them to use only State or Federal based control where a private surveyor can often choose to use any of it depending on what they are working on.

 

The Truth is that not all Geodetic Control stations are as valuable as the next. The Ones that comprise the NSRS are currently considered the most valuable. CORS, HARN, HGPN, Airport control, and other highest accuracy control are going to take precedence over lower quality third order control. GPS Derived positioning is generally accepted as having higher accuracy than that of optical work. That does not mean I would not use a Optically leveled Bench or an Optically Triangulated location for positioning. I can, I have and I will again. If a developer is developing a plat for new homes in a small rural town and all the control there is old control, guess what you are going to use for control?

 

The Truth is that these stations are *NOT for boundary work. But they can be included as a part of boundary work.

 

What I mean to point out is that you have been told how the State of NM is looking at things, but it is not an all inclusive opinion. Nor is it the way all states do look at their networks. Remember there are 50 states and a lot going on in all of them. It seems reasonable to say that while your contact at State is aware of his State's agenda, he may not be as aware of what else is happening in the industry, or even how others in his state will want to use survey data for control.

 

Just because someone working at the State level does not see a portion of older NGS control as important to their work, it does not make the control bad or dated or inaccurate, or as having no future. They are just calling it as they see it based on the methodologies they follow.

 

As a closing thought and for example, the Rockhounders have been out to some of the most remote locations I can think of and have recovered monuments there. They have asked off handedly in the past that it seemed odd that survey markers were there. They felt they likely had little importance, as it would seem there was no reason for a survey marker to be out in the middle of no where. Further they asked why recover them? No one has since they were put there. They made an excellent case!

 

But the monuments were put there, because as geodesy grew up, those locations played a part in figuring things out, and they are still there. Before they were surveyed in, we knew nothing about those areas. That is how we learned what we know. Will they ever be needed again? Well Mathematically they do get used in house for big equations here and there, they were also used in least squares adjustments as well. Will a housing plat or a new freeway use some of those old remote markers? Probably not but we never know.

 

On the other hand we often hear from our friends who work the area near Washington D.C. area that a good bit of the control has been wiped out due to Urban Sprawl. It is conceivable that some of the control they cannot now find was used to help develop local control networks before it was lost. Some of those old stations were once seen as being remote, but are now displaced by a strip mall.

 

So we can see, all this stuff can be important in ways we might not realize, and when we consider the new and very young computer age, the possibilities that have become reality today were not even a twinkle in the eyes of people who were a part of all the survey work done in the 1930's.

 

My take on it is that we are doing a good service here. it is not up to us to second guess the future. We are being helpful in our recovery efforts, it is best left to each state or locality to determine what is isn't ore will be useful to them. Thanks to us, at least in some cases, they will know what they have.

 

Rob

[Bill93]

The quote above says "The use of the NAD 27 map projection is one of the main reasons for our abandonment of these old monuments."

 

Is he saying that the NGS data sheets with computed updates from NAD27 and NGVD29 to NAD83 (pick a year) and NAVD 88 are not accurate enough for their purposes?

[evenfall]

Bill,

 

NGS Data is as accurate as it gets. They are the reference standard. If NM is using a Datum, And they are, they are only as accurate as the keeper of that datum. The difficult thing is that NM does not use the internet for it's survey markers and not being a really populous state, city wise, there are not a lot of other opportunities for other control networks.

 

Wanna see where NM bases it's Survey Data accuracy on? Here:

 

http://www.ngs.noaa.gov/INFO/OnePagers/NSRS.html

 

And Here: http://www.ngs.noaa.gov/CORS/Southwest.html

 

Oh And: http://www.ngs.noaa.gov/PROJECTS/FBN/

 

What the Guy from NM is likely saying is that there are varying levels of control and they are thinking of keeping pace with the new modalities. This means using GPS as much as is possible and keeping standards high which mean that for his organization, Tie ins to the old third order quality stations are not going to cut it.

 

They want A or B order Value as based on CORS, HARN and HGPN Networks, and as such, so they can get the highest accuracy they can get. And in their case this is likely either NAD83 (1992) or NAD83 realtime CORS tie ins.

 

It is all good really, they are just coming from a level in the State Agency where they do not consider the lower order control important to them. Regardless to their position on this, other agencies within the state will find third order Triangulation useful for some of their projects and they will use it.

 

Another way of looking at it is like a little girl who likes to eat skittles but she does not like the pink ones. She would not share a green one or a yellow one with anyone, but you can have all the pink ones you want. Well NM likes the yellow and green ones a lot, and though they don't care if you like them too, they want nothing to do with the pink ones. Just a choice.

 

You never knew Survey Markers and Skittles could be used in an analogy did you?

 

:-)

 

Rob

[Bill93]

If I read you right, and his problem was with using lower order stations, then he should have said so instead of implying the problem was with the original datum.

[evenfall]

Bill,

 

It isn't a Secret. CORS, HARN, HGPN, FBN, and all considered High priority NGS Survey.

 

The Highest priority is to work with the Highest accuracy possible, and that is as simple as following the 80/20 rule.

 

As of this writing, NGS is ramping up on a new adjustment of the NSRS and hope to have it finished within the next 2.5 years or less. The Criteria was to observe only submissions made by GPS observations. No optical values were to be allowed in this readjustment and by so doing the the Higher accuracy that GPS is capable will keep the averages high in the final outcome.

 

This Person we are referring to is not being disparaging towards the lower order survey markers, it is just that there are varying levels of accuracy quality in NGS control and his Intra-agency rule is to stick to the higher quality stuff.

 

Bottom line? NAD83 is a datum that has a number of sub adjustments that depending on the coding belong to specific areas. To add, it is a keeper of data for survey markers of which have only been worked to a certain level of quality.

 

For the best understanding of how it all fits together conceptually, Do some reading at the NGS website and try to become familiar with what the CORS, HARN, FBN, CBN, and NSRS are and how the interrelate. Also, look into the various levels of accuracy are, for both horizontal and vertical control. Once you begin to understand how some of the special projects overlap, you will begin to understand why many of the old third order surveys are not as important to some agencies as they look to the future rather than the past.

 

Like I said. The Old optical survey is not dead, but there is limited money laying around so the mission is emphasizing the spending on plans to create sub networks of higher accuracy and from those observations, everything gets lifted up. And if the old third order mark is ok to use and it is handy, Many surveyors will still use them. It just depends on the engineering requirements of any given project.

 

Finally, let's look again at what the Guy at the NM State level said. he said: "We no longer consider control as a permanent feature given the relatively easy task of establishing quality control on our roadways. We basically bring in new control for any new project in a matter of days unlike previous decades where terrestrial control could take over a month of control surveying. Our control is now evolving in the direction of an almost disposable quality due to the high cost of maintaining current control networks." His "agency eye" is on the future, not the past. He is clearly a fan of GPS Derived Survey control. He feels it is more accurate than NAD83 Adjusted and transposed NAD 27 and NGVD 29 control. But more that looking down on the Datum, he is looking down on the orders of accuracy. He simply intermixed the concepts and hey, that is easy to do.

 

If I can tie to my CORS, HARN or FBN, as networks of high accuracy, then by simply walking out and setting up the GPS for developing Horizontal Vertical and Elliptical Control, sequence of Survey Marks as an on location master station, complete with all the subsequent survey needed therein, then you see how some things can seem disposable. Much of what a surveyor does, especially from a construction point of view is a disposable form of stationing. All this guy is saying is that we are now entering an era where we can rapidly develop High order accuracy networks for projects on a local level, without having to worry about the cost of having to maintain it. We can position that good with GPS Now so why not do it? This is just beginning to come over the horizon now, especially for Vertical control.

 

Does that make better sense?

 

Rob

Edited June 3, 2005 by evenfall

[Bill93]

"But more that looking down on the Datum, he is looking down on the orders of accuracy. He simply intermixed the concepts"

 

So we agree. Thanks.

[Z15]

One thing also it that a lot of the old control has now grown over the last 50 yrs or inaccessible. In my area about 1 in 100 are in the open and can be used without having to cut trees or brush or traverese many miles. Most all of the survey crews are now one or two men operations and its time consuming to do conventional work with a small crew.

 

In our area, 99% of the Azi marks are not longer visiable from the ground at the stations.

 

The DOT is mapping a stretch of highway near me. 90% is being done with GPS and what can't, is done with a conventional total station. All control is new GPS. They have a GPS antenna rigged to the side of a Chevy Van, they drive the road, stop and take a RTK reading and move on. Don't ahve to get out of the truck. So far in 3 days they have mapped about 5 miles of roadway, the old way woull take them 5 weeks or more. With the new technoogly, the data can be on the designers work station the next day. What used take 3 yrs to get a project to the build stage can now be done in 6 months or less.

 

Anyone who ever worked on a survey crew before GPS would be amazed at the amount, speed and accuracy GPS gives you.

 

I think this is what the NM eng was trying to convey.

Edited June 3, 2005 by Z15