ALTA Measurement Standards
ALTA measurement standards require a 0.07 feet plus 50 ppm RPP. In school we post processed a static survey and traverse using TBC. We achieved our goal of meeting ALTA standards. We use Topcon equiment with Carlson and C3D software. We download text files but no raw data. I would like to know if it is necessary and how to post process GNSS network data for an ALTA survey. I dont know of another way to test against ALTA standards. I have seen in my area that it is uncommon to run tests for ALTA standards. The standards say to run a minimaly constrained least squares or a covariance matrix.
After all if that, is it normal to not run data analysis? Should I run the analysis? How do I use carlson to run the analysis?
MINIMUM STANDARD DETAIL REQUIREMENTS FOR
ALTA/NSPS LAND TITLE SURVEYS
We download text files but no raw data. I would like to know if it is necessary and how to post process GNSS network data for an ALTA survey.
3. Surveying Standards and Standards of Care
E. Measurement Standards
i. Relative Positional Precision can be estimated
by the results of a correctly weighted least squares adjustment of the survey.
How can you post process GNSS network data without raw data? You wrote that you only downloaded text files. If it's uncommon in your area to run tests for ALTA standards, then it seems to me that the standards aren't being met. Please explain further.
ALTA measurement standards require a 0.07 feet plus 50 ppm RPP.
After reading the standards again, in particular 3.E.v.
It is recognized that in certain circumstances, the size or configuration of the
surveyed property, or the relief, vegetation, or improvements on the surveyed
property, will result in survey measurements for which the maximum allowable
Relative Positional Precision may be exceeded in which case the reason shall be
noted pursuant to Section 6.B.x. below.
A note on the face of the plat or map explaining the site conditions that resulted
in a Relative Positional Precision that exceeds the maximum allowed pursuant to
I'm just guessing, but maybe the fact that it's uncommon in your area to run tests for ALTA standards is due to the circumstances noted in 3.E.v.
Many firms ignore this and other inconvenient standards like setting missing irons.
The PLS may not have read through the standards thoroughly. More likely he has and doesn't understand what it means or how it can efficiently be accomplished. It might be a good opportunity for you to figure out a new workflow.
Yes, you need the raw data. Bring it in to SurvNet and there's a feature, similar to TBC, where you can create a Least Squares analysis that includes ALTA tolerances to the control and monuments of your choice.
No raw data is being exported. I would have to do it myself. I did not know if there was a way to run an analysis in x,y,z coordinates. I will have to download the raw data and tinker with it.
There are some projects that it is difficult to meet accuracy standards. We have done work at state parks. For the most part, we are at open and flat commercial and industrial sites. If there is an issue getting GPS to lock, we break out the station. Let me know if you need more information.
The pass or rail criteria of relative position precision comes from a properly adjusted Least squares adjustment and two ways they give us to test or solve this by the semi major axis or covariance matrix information that comes from the adjustment. I have seen several firms not use and not test this . When asked they say i met my state standards and thats all I desire to do. A lot of surveyors do not use least squares or even have software that can do this. So the still use compass rule. I do not knock them I would rather see someone use what they understand and have knowledge of then to do something they do not have the understanding of. It is a sticky point the way ALTA defines it relative position precision and how to test it basically tells the Surveyor he/she must use least squares as adjustment. That raises the hairs on some surveyors. As they want to choose adjustment types based on their knowledge and tools and what they deem to be best in any given situation. It is simple math after a least squares has been done to check everything. I used a simple excel spreadsheet until I realized that my software had a built in report already. Then i simply checked it long hand by spreadsheet until i was comfortable that it was doing what it was supposed to do. I still ck my shortest and longest lines by calculator and one other random line. Software gets updated reports could catch a bug. Lol.
I do not knock them I would rather see someone use what they understand and have knowledge of then to do something they do not have the understanding of.
I agree with the sentiment that they shouldn't be doing things they don't understand, but at the same time the minimum standards are clear. If you're not performing a LSA, you're not adhering to the MINIMUM standards.
If you're not performing a LSA or don't know how to, you have no business performing ALTA surveys. Doesn't matter if it's "just a survey for a loan".
When asked they say i met my state standards and thats all I desire to do. A lot of surveyors do not use least squares or even have software that can do this. So the still use compass rule.
Which is no excuse because a lot of states have RPP standards too. In Washington State relative positional precision is to be used when work "is not amenable to analysis by traverse closure", so as soon as you throw GNSS observations into the mix you're now required to use RPP.
With modern equipment the ALTA standards of 2cm+50ppm at 95% are pretty easy to meet, even on densely wooded and rural tracts. When practitioners fail it's usually due to not enough redundancy.
No raw data is being exported.
This is just a massive red flag, especially when doing ALTAs. Danger Will Robinson!
@steinhoff so true. As I study and prepare for state exam i am often told by some of these same professionals that no professional should practice outside of their expertise. In all actuality it is not hard to gain the knowledge and experience needed to do this. I use the estimated way of testing by the semi major because it is math that most surveyors are comfortable with versus the covariance matrix information. It is simple to explain when they ask me about said alta report coming from TBC. And they can use a calculator to solve as a check. I agree on if they do not know how to meet the minimum standards then don’t bid on that type of work. Same applies to bidding on static control networks or level lines for control. Had a surveyor i knew bid on a project that required first order levels. His idea was read the 25 ft level rod to 3 decimal places and if his closure met specs all would be good. They re ran levels several times. He called me when his data was not accepted by client that was blue booking it. I told him that he needed to walk away from 1st order levels he did not have the equipment or know how. 3 months later he called sent me the information on a 2nd order class II level line. Once I explained to him what all was needed he said i am walking away and that didn’t require gravity readings etc. he simply didn’t have a auto level and rod or the manpower to actually accomplish that sort if thing. Now we have digital levels and people think because they have a digital level then they are performing 1st order levels every time they run around a site. It is stepping outside the knowledge base. I have helped from a distance years ago guiding some ls surveyors on some of this work. As they studied and pursued the work. Thats a bit different than shrugging the minimum because they don’t want to. I don’t even want to run 1st order levels. 2nd order class II is about where I would want to stop and I have done the other. In a land surveying setting it is not done with a crew often it will cost more than you make. It takes a well oiled crew to run levels any distance at those standards. I think even the old ngs folks that did nothing but levels every day averaged about 5 miles a day. You just can’t do that with a crew that does it once or twice a year. Or on some small job site every now and then.
@rover83 so true. Some states use a bit of different in definition than alta. Alta is semi major axis. If I read correctly. A nearby state sais in both semi major and minor axis. But the word REDUNDANCY is key. You are so correct. Rtk static or even a traverse that is the key and can save your rump. Lol. Redundancy is so helpful and is much better to get it on front end vs going back out.
His idea was read the 25 ft level rod to 3 decimal places and if his closure met specs all would be good
thanks for the laugh.... that's a tragically funny thing and Indicates maybe his work needs to be reviewed for relevant accuracy and credibility....wowsers.... 🤯
With modern equipment the ALTA standards of 2cm+50ppm at 95% are pretty easy to meet, even on densely wooded and rural tracts.
Please refresh my old brain regarding the term 2cm+50ppm. I'm used to seeing standards defined as a ratio like 1:10,000. Someone on these forums explained it to me once before.
Which is no excuse because a lot of states have RPP standards too.
What does RPP mean?
The other aspect of least squares that nobody talks about, and the rules don't specify, is whether the program takes the standard errors you give it as fixed or if it scales them all proportionally according to the goodness of fit.
Star*Net leaves them alone unless you fail Chi-squared on the high side and then it scales them up. It uses Rayleigh statistics.
Some software, I think, estimates your goodness of fit and then scales the std error values you gave it, regardless of pass/fail. These use F-distribution statistics. Wolf & Ghilani's text illustrates this method.
One method may be more optimistic about how well you measured than the other. I forget which is which.
That means your pass limit is never less than 2 cm, but for long distances it will be larger. For instance at 300 meters, 50 ppm is 0.015 m so your limit is 0.02+0.015 = 0.035 meter.
Works the same way converted to US units.