Helmert's Transformation. A least squares best fitting.
How do you shift and rotate one data set to another using more than two points?
You can't, or at least that I know of, but that would be a question for someone with more familiarity with TBC than me. Like you suggested the other points would be used as checks.
ditto
As others have mentioned I used Trimble Access and Trimble Business Center. One data collector one job file all on the known Datum and projection almost always state plane.
In TBC I have had jobs where digital levels along with static and total station data along with RTK . I bring all data into a TBC project on the state plane. If the job requires ground I do my scaling in TBC by finding the best combined factor via looking at the average ellipsoid heights and creating an orientation and scale point. Then I performed least squares on observations. This allows me to have a project coordinate system at the surface or aka averaged surface and also be able to switch between true grid state plane and the project coordinate system. Trimble makes it very easy.
Most companies that I worked with usually set a pair or two with GNSS choose a point and scale those to ground and then use total station or robot to be at ground and do whatever else work. This can be done by scaling from a point or at an orientation of 0,0. I don’t like the whole choose a point and scale as no thought is made in seeing if that one points elevation is close to and average for a site it does work most of the time for being good enough in most scenarios. This would be in theory the same issue of scaling in cad you are using one combined factor for a site. Every points combined factor is unique to the scale the elevation or ellipsoid factor to create a combined factor. I basically try and follow a process in which I get the best possible solution for both worlds. Now again 99% of the time it’s not a big difference doing this .
With today’s technology in all honesty it’s not that hard to just stay on grid all the time as we have to scale something one way or the other ground distance to grid or grid to ground . I can understand back when 99% of the work was done with a total station and all the computations were done long hand to scale the ground distance to grid but the software does all of this for us .
We have lost the understanding of what all is going on today I see so many people use the scale factor in cad from a NGS data sheet which is incorrect I also see those who know we need to use the combined factor from a NGS data sheet but they use it incorrectly as they assume it is for grid to ground but its ground to grid . Here it’s roughly a tenth of a foot per thousand feet so we have a few miles project and in their head they say well we have all this error from one end to another so we must use ground they are not traversing from one end to another so why not stay on grid set points along the project on grid where it is feasible and mitigate the density with total static that also uses grid . Then if you truly need a ground system scale everything back at once for a more efficient project factor.
It is not that hard. Now I do understand the need on certain projects for sure but most here are not going to be affected either way as long as everything is on the same system
I've been using SALSA for about three years, it works great, we wrote our own software to convert Trimble JobXML files and project files from Topcon's GLS 3D Laser Scanner, so we include GPS, Total station, Level and Laser scanner observations. 😉
Generally we use a minimum of three static positions, a maximum of four, two of the GPS antenna's have prisms underneath so we can set all static positions up the day we get there and then resect off the two that have prisms. If it's a long job, we break static GPS obs up into weeks and process them 1 week at a time through AUSPOS.
I love your integration of GNSS antenna and prisms pfirmst.
I tried using SALSA before but gave up on it, I lacked the intellectual ability to figure out how to use it properly (I'm too dumb and/or lazy).
I can show you a small job if you like, it's fairly simple. The hardest part is entering covariance matrices from Sinex files.
I use TBC to handle observations and adjust, entering elevations from leveling as control. And I only bring scaled ground points into C3D. I don’t trust it to scale data. Bring it in finished and with no allowance for a setting to move and mess it up!
I'm late to the conversation because I rarely get on here, but great responses. A properly weighted least squares adjustment is your friend. Reminising of doing this before there was easy LSA software from the equipment manufacturers, but Paul Mystric of Canada GeoLab Software was the bomb, I started using it and working with Paul when we were using UNIX based computers before PC's. You had to dig into the equipment specifications for each data source instrument for instrument standard errors, use some logic and experience for observation standard error weighting and play with it. The goal was not to put some global scalar to make the adjustment match the statistical tests like Chi-Square test. And chasing outliers and deleting observations if need be was part of the fund hound hunt of getting the best solution. Usually, we would work with our best known data set such as GPS vectors once that was available and keep adding the other data sets in one at a time. Ah, the good old days, thanks for prompting this old dog's memory, it's not really very good these days but I have moments.
I am teaching a crew now doing this very thing. Base rover rtk network RTK to get started from and robotic total station. This is all in Trimble Access and the qa/qc and LSA will be performed in TBC.
Arrive to site break out the R12i do an observed control point via network RTK. Set base up on said point. I always do RTK and logging as an extra check to send off to opus. It takes no more time. Drive to another great location for the base to be moved to. These do not need to be inter visible they are the best open sky I can find on or off the site. Rtk a point observe control method via base rover. Switch to network RTK observe again same point name. This gives me a Ck later on any rotation as technicaly the direction or azimuth for gps is good within the observation error. Start setting points inter visible where needed for robot locate property corners and any mapping or Topo as time allows. At about the 4 hr mark depending I have usually hit many points once via base and rover depending on site size I may have done another network RTK observation on another point for possible base location. Move the base to the other point set up on it RTK logging. Run the circuit back through all points again including the first base point. Next day or same day the robot can be set up and rounds turned mini traverses cross ties made all in same job file. Like mentioned above you need to keep the law of averages kinda in your head as you might see more error between points that were RTK derived than just a robot relative precision. If Thad a bad shot on a observation this could have you chasing your tail. Just for example let’s say you have a 0.2 vertical error on a bs and you have double checked the hi and target height. I keep moving as I know Trimble accusing using one of the observations and if I used two the odd are it’s half that. I usually check the data daily in TBC I have a list for the next day for crews to re observe at a different time those outliers that raise there head. It’s usually the ones we observe in canopy. But usually even then a third observation via RTK or when you have connected to other points with robot you can disable the bad vector before or other observation before the actual least squares is performed. I do this daily and keep a list as they work through a project. It’s usually only takes a small amount of time and by the time the project is done I have a good idea exactly what to use and not use and the least squares is quickly done and all data has been qa/qc and now ready for drafting and surface contours ready. I usually send the logging files to opus and name them accordingly and this lets me choose the opus or network solution for my primary position. In all honesty there is usually not a nickels difference in most cases the network for rtk is tied to CORS so it’s a sanity check. That’s how it’s done majority of time. When I have my way I do all the boundary corners and control first no mapping. Do least squares and make a new tbc project with the adjusted control. That way daily files for mapping and Topo come in and my screen is not so cluttered. But reality is that is not how bosses want things done so I am flexible and work through it.
I have about 2000 acre boundary coming up where I will use fast static RTK base and rover on and robot. 7 or 8 tracts inside to be all combined vacate the lines. I will work from center out and surrounding my total site via fast static non intervisable primary control. Then use rtk base rover along with robotic to fil in gaps where necessary. We actually have to be creative in setting a good network design as we don’t have sections but very odd irregular shaped properties. As well as finding holes or open areas to set control in. Because of so much canopy. While google earth is awesome it is a different story when you get to a site that was timbered 15 years ago now it’s so thick you can’t see 50 ft in front of you much less get a clear sky. So often it’s on the fly designing the geometry. Sometimes it’s impossible and law of averages as the statistics often don’t show that you have a good position because so many acute angles in observations so a lot of looking at the spreads of multiple observations is a better indicator in those situations and common sense to know you have a good answer that works.
I always tray and picture my site as a wagon wheel with spokes working center to outside the property. Then closing the triangles around and inside the site. I have added NGS CORS data to help strengthen my figure of a site to the base stations that we’re logging and it improves the statistics but the end coordinates didn’t change enough it was all about the geometry for the final results. I try and achieve a tight tie to the NSRS while maintaining more focus to the relative accuracy of the site its seals that’s the boundary side. You can achieve both. And it’s all about for Trimble in having a good naming convention where point 1 is always point one no matter how from where and many times you located it makes it so easy.
I used to do the “adjust control first” - then not use TBC again but now I keep all my data in one VCE file and keep adjusting it since it’ll use total station bscksights and observed angles to other control points plus new control set. I use integrated surveying 98% of the time
Yes. TBC has its issues but it has to be one of the best tools for managing the data on a project that utilizes different sensors like gps robot etc to keep easily updating until final delivery is ready. I wish they would update it more to have more drafting abilit compared to civil 3D and Carlson CAD. But it’s not to bad for me but as I learn more in the other CAD platforms I can see why those who are use to that like cad better for sure. Integrated surveying is so beneficial once people wrap their heads around it.
