so after all that vibrant discussion... any takers on how to perform the LSA appropriately in C3D?
I recommend this book for Civil 3d. It has about 20 pages on running an adjustment.?ÿ Plus, you need to start with a .fbk?ÿ raw data file.?ÿ After you have read it you will probably be cured of wanting to do adjustments in C3d. But maybe not.?ÿ
The book is still worth it for the other couple of hundred pages. It helped me a lot in transitioning from LDD to C3d.?ÿ
It kinda does that, however with TBC you need to be very careful how the file and shots are done. Stakeout shots need to be treated differently, I had a long convo with Trimble designers about it and they will not budge over the Stakeout shot issue. Stakeout shots are considered sacred in Trimble. They will not get recalculated.
However, you may convert the stakeout points in TBC and then they will move to the proper position.?ÿ
?ÿ
Stakeout shots need to be treated differently, I had a long convo with Trimble designers about it and they will not budge over the Stakeout shot issue. Stakeout shots are considered sacred in Trimble. They will not get recalculated.
Yeah, I don't know why it takes crews so long to wrap their heads around the idea that if they're not staking a design point, they can just shoot it with the same point number.
Access gives you deltas to any existing point you re-observe, and the opportunity to store it, override, average, check shot, etc. No need to stake it out or shoot a different point number then inverse.
Stakeout points in TBC have explicit delta values with respect to how you told Access in the DC to calculate the position, so it would be imperative to assign them special quality/status to maintain the true record of the field work.
(I'm aware you can convert as-staked points so they behave normally.)
If a stakeout point were required to have additional qa/qc and/or LS statistics, i would hope the surveyor would wrap sets, or obtain independent measurements to validate its as-staked postition.
Access gives you deltas to any existing point you re-observe, and the opportunity to store it, override, average, check shot, etc. No need to stake it out or shoot a different point number then inverse.
This is probably the most significant difference between Access and Survey Pro, and IMO, the feature that makes Access a superior product.
It's an entirely different mindset that lends itself towards mixing data sets in a comprehensive manner, just how LSA treats various data sets/sources by individual PID.
@rover83?ÿ
There are many features that I like in the newer access and TBC, all the routines can be very automated. POL's on a staked line will still come up with a staking report and from what Trimble told me they won't adjust a stakeout point (been a few years). So when you change the value of the base point the stakeout point remains the same, until it's type is changed by edit.?ÿ
I just want them to be placed correctly by vector from the base point when the file is recomputed, I don't see how that invalidates the points. However, we do the work around and delete the stakeout points and all is good.?ÿ
I agree with your sentiment, and I too, do like you with the as-staked points.
I wasn't trying to imply that points are/were/become invalid.
In the prior post, I was thinking (but didnt type) that I suspect the as-staked points are given special status so any number of the various reports can be run from the DC report list while maintaining a solid link to the field measured data. At the end of the day, you have to "pick a measurement" to hold and base a comparison upon.
Apparently I'm driving the struggle bus today, and can't communicate worth a $#@!
I couldn't imagine trying to program/write code that allows Access to: function well, track real time changes, monitor the accuracy of said output while being able to address the ability to stake out a desired position with respect to another point, 2d polyline, 3d polyline, 3d surface, road template, regular geometry shape, etc.
?ÿ
If the base point is subject to adjustment I will usually stake the point on line then locate it with measure point, which allows it to shift with the new base coordinate.?ÿ
I just want them to be placed correctly by vector from the base point when the file is recomputed, I don't see how that invalidates the points. However, we do the work around and delete the stakeout points and all is good.
Presumably the operator is setting stake points in the correct place from established control for the purposes of layout. From the software's point of view, why set a hub & tack for construction if it's going to move after post-processing? The idea is to maintain data integrity, and show office staff exactly where the design point is at the time of staking, plus the deltas that the crew observed and accepted for that point in real-time.
It's easy to get into the weeds about best practices depending on how large is the project, total duration, type, etc.?ÿ"Properly" controlling a site with the ultimate goal of staking/building a project could vary from a subdivision lot stake to building a microchip fabrication plant, and anything in between.?ÿThe beauty of LSA is that it can have a useful place within each of those use case scenarios.
I've been on the receiving end of a Civil 3D least squares adjustment @$$-whooping more than once; nothing nice about any of it.
This whole discussion thread boils down to having a few "good" tools (software/hardware), and being able to use them in the way they were intended. Anything else is just asking for trouble.?ÿI understand that not everyone has the latest and greatest, or unlimited money, but buying good software and hardware is well worth the expense and trouble to get it. And for Pete's sake, get the training too?!
When all you have is a hammer, everything starts to look like a nail. If that's the case, then you've alread lost.
Not sure any of this helps the OP, but it pains me to hear a surveyor talk about how they have to use C3D. And I know plenty of small survey shops that choose to use it even though they don't have any engineers, nor do they feed engineers.
@rover83?ÿ
The points don't move as the base point does, for instance setting a base up for a boundary, the corners are located, then line between is set, when the static file for the base is processed and the base is shifted to "real world" coordinates and the file is recomputed, the measured points such as boundary monuments will shift with the base, but not line points that were staked out. So the line points appear to be off-line. In TGO the stakeout points would shift, but not in TBC.
What is more startling is if a stakeout point is 100' west of the base, the base is shifted 5 feet west, the file is recomputed, now the vector from the base to the stake out point will be 95' long.?ÿ
@rover83 oh you are preaching it brother. ?ÿI still don??t understand why someone takes a backsight with Trimble access. Then they turn around and stake the BS out. Then off to a third point check by stake out. This is not the 90??s anymore. Heck if I go back to a site and all my control is in and been adjusted i use the ck shot routine its one nice little report i can easily look through to see if the checked in at every set up.?ÿ
Managing point names is key for Trimble access and TBC. If that is right and you have your standard errors and such set you will eliminate most blunders fairly quickly or at least identify them from import because of the red flags or yellow warning flags. I usually run a completely unconstrained adjustment first to check the observations and see if i have my weighting correct. Because we don??t have any set procedures i get networks with rod and pole traverse with direct readings along with traverse kits rtk resection??s and different specs on instruments on same job site. Some keep equipment in adjustment some who knows. Based on mean angles i see all sorts of garbage. But through redundancy and LSA I get it to fig inside a pie plate lol.?ÿ
False equivalencies.?ÿ Recently, I've been on the way home rather late and wanted a drink.?ÿ There is a small gas station / convenience store on my way that was closed but I knew it has a drink machine outside that only accepts cash.?ÿ I stopped and got a drink.?ÿ Even more recently, I've taken a family member to Vanderbilt Hospital very early in the morning for a procedure and wanted a caffeinated drink.?ÿ Their machines only accepted a card.?ÿ I enjoyed that drink as well.?ÿ I'm glad I didn't lock myself into only one or the other (the drink at the gas station with cash was after a very hot day, so the cash instances was probably more satisfying).
Been out working all day and was really looking forward to a clear answer to something I've not understood since the 1990's when I first started reading research papers that would state LSA is the best method for traverse and network analysis and adjustment.?ÿ The papers would then go on to explain that traversing was the standard way of conducting a survey (yadda yadda yadda) for about a paragraph and then jump immediately into the idea of network solutions.?ÿ Application in network solutions is very easy to understand why LSA is better as the observation equations allow for determination from several different directions and some meaningful (in my opinion) analysis of the results.?ÿ Whereas on a closed traverse, it appears to me that you can really only develop two possible point locations and then average them for the most probable.?ÿ Given the positioning of those two points and the direction the observation equations would have to flow, the result is not (as far as I have been able to tell) better than a compass rule adjustment, just another way to accomplish the task.?ÿ Further, LSA seems to accomplish the same thing of scaling lines and closing the figure so as to also adjust the angles that a compass rule adjustment accomplishes.?ÿ Which is why they are pretty much the same coordinate for a closed traverse.
The question of what it brings to the table for a loop traverse has been rooted in those 1990's (and onward) readings as those papers always seem to jump very quickly to networks instead of a closed traverse.?ÿ But that question was brought to the forefront when Ricklife sought help on this board with his busted traverse.?ÿ The data was not ideal (procedures probably matched a significant amount of work done around the country) and would have benefited from some different field procedures more than anything else.?ÿ However, it was least squared and reported on.?ÿ More than once it was stated that the data was not blundered and that with some minimal wrangling it passed the chi-squared test.?ÿ I can buy that as the problem was not a blunder, but instead a very significant systematic error. (Although I have always understood an assumption of least squares was it would be applied to random errors, not blunders or systematic errors)?ÿ Even after two data sets with significantly different angles reported (as much as 2 minutes) were posted, it was stated that after discarding some outliers, the adjustment was good and that the data wouldn't be considered a busted data set.?ÿ Frankly, being able to see significant differences in observed angles in the raw data, which would suggest an instrumentation problem, yet throwing some outliers off and accepting the rest of the data as "not busted" because the LSA software was able to calculate a passable solution increases my concern of what does it bring to the table for a simple closed loop even more.?ÿ If he had run even a single cross tie, then LSA would probably have been all over the problems at each angle.?ÿ But because there was not appropriate redundancy, it appears that a systematic error (when just small enough) was simply incorporated in an answer with only a few outliers being considered "bad data".?ÿ That scenario is frankly quite enough to raise a legitimate question of, within the very minimally redundant closed traverse what does LSA do for me that is objectively better.?ÿ?ÿ AND that is a vastly different question than what's the good of least squares.
@jon-payne Great question. ?ÿI never have looked at any adjustment LSA Compass/Bowditch Krandle Transit as being able to fix bad data. If I Identify bad data no matter what adjustment I can make work or pass is the best outcome. Thats when re observations are needed. LSA will show systematic errors. Now lets take the simple traverse minimum redundancy closure LSA vs Compass/Bowditch method. ?ÿBowditch distributes the error equally throughout the traverse. Simple stated angle and distance error. LSA looks for the best fit of least movement of all observation all at the same time. Now the statistics will show where a possible blunder or systematic errors are occurring. If you run a traverse data set of a simple traverse through compass rule and then lsa. You will see that if it was a kinda loose traverse how the center going around from start has the largest error ellipse. Sometimes and with lsa even though coordinates match withen tolerance of the compass you would see a little different in the error ellipse. Possibly. ?ÿIt truly depends. But for simplicity its a way to explain. ?ÿSo for what it does for you is identifying a possible blunder area of the traverse. Much like the old arc tangent of the missed closure to point to the side or angle that might be the issue. Its just a tool method to aid in identifying at that point. If you have good field procedures balanced traverse lines good geometry is then it is a moot point. But when you have an issue it gives you a little better warm and fuzzy on where to send the crew back to check an angle vs re running the entire traverse. ?ÿLSA doesn??t fix bad data it just makes it easier to find the bad data . Now as you kinda stated if network and have extra redundancy then a trip back out might be unnecessary. ?ÿ
The reality is we run around the boundary traverse. We run inside the boundary to locate a house driveway utilities pond etc. why not throw extra measurements to other control while there. Often times people do the whole traverse main control. Then traverse for other locations and just do a point closure as a check. ?ÿWhy not use that data. ?ÿ?ÿ
That scenario is frankly quite enough to raise a legitimate question of, within the very minimally redundant closed traverse what does LSA do for me that is objectively better.?ÿ
Remembering back to learning about closed loop traverses analyzed with LSA, I recall the lecturer stating something to the effect of, "if you don't set up 1, 2, x times in the middle of your closed loop and get non-adjacent point cross-ties, then you really have negated the value of LSA on closed loop traversing."?ÿI think that's what you were getting at, yes?
The question of what it brings to the table for a loop traverse has been rooted in those 1990's (and onward) readings as those papers always seem to jump very quickly to networks instead of a closed traverse.
I think you may have overlooked this aspect: properly designed and conducted field work with LSA in mind for the ananlysis will always yield "networks" with independent/redundant measurements.?ÿ
Example: 3 legged closed loop traverse (triangle).
Set & occupy 4th point in center of primary closed loop triangle and take angle/distances from/to each of the permiter 3 points. That's a network of 3 small triangles within the big triangle now. Pretty tough to get better than that.
Maybe the discussion in the 1990's papers you read didn't give this last crucial detail, but I got the impression that you thought the papers quickly jumped to the discussion of GPS networks, and left the traversing incomplete?
The "network" aspect of the LSA is designed by the operator, and a simple closed loop figure is not a stellar example of best practice for LSA, as you were pointing out.
I watched feverishly from the peanut gallery as all the members crunched the data to resolve that traverse issue described above. I have to pick my battles to get involved with the help, else I will go down a rabbit hole out of sheer curiosity and enjoyment, even if I shouldn't, due to time constraints.
?ÿ
Star*Net and probably most LSA programs will weight the angles with a proper combination of what you give it for instrument accuracy, instrument centering accuracy, and target centering accuracy with the nominal length of the line to form the standard error of the angle measurement. This alone is an improvement over compass rule.
Closed loop traverses are condition equations.
Multiple cross ties or resections or breaking setup for more obervations = observation equations.
WIth the advent of modern computing power, the condition equations are a step backwards.
?ÿ
LSA can be glitchy,,,,or odd.?ÿ
Doing GPS adjustments I've always processed each vector before doing the LSA.?ÿ
I've seen many times the coordinate from the LSA fall outside the individual numbers.?ÿ
For instance an ellipsoid height of 100.10 from CORS point to the NW and 100.06 from the CORS point to the SW and the adjusted number is 100.11. No big deal for the most part but I will often override the adjustment and mean the value, same for lats and longs.
LSA can be glitchy,,,,or odd.?ÿ
Doing GPS adjustments I've always processed each vector before doing the LSA.?ÿ
I've seen many times the coordinate from the LSA fall outside the individual numbers.?ÿ
For instance an ellipsoid height of 100.10 from CORS point to the NW and 100.06 from the CORS point to the SW and the adjusted number is 100.11. No big deal for the most part but I will often override the adjustment and mean the value, same for lats and longs.
That's a function of the network adjustment transforming GNSS vectors to local datum i.e., NAD83 ellipsoid heights, local ortho elevations, grid north/east, etc. In TBC the latitude/longitude deflections option defaults to on - it can be turned off, but it really should only be done in certain cases.
?ÿ
A good example: when doing airport/AGIS work, we had to fix the PACS & 2 SACS that were only a couple hundred meters apart (because they were our only primary control in the area) and clustered at the center of our work.
But our observed points for aerial targets were miles and miles out from the runway/airport itself. In this case turning the transformations off during adjustment kept the network from being warped at the outer edges due to holding 3 control points very close together at the very center.
If you're holding a single point fixed in the vertical, it will just shift the GNSS vectors "up" or "down", so depending on the location of the project and the values being fixed, unfixed (derived/adjusted) point values may not look correct, at least not intuitively.
But it's not a "glitch", it's exactly how LSA functions. It can only do what the operator tells it.