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How do you handle SPC on your projects?
Posted by OleManRiver on January 15, 2022 at 4:38 pmHow do you handle the SPC values on your projects? I am not here to debate Grid Vs. Ground or LDP’s. What I am wondering is when you go out and establish starting control via OPUS or RTK or RTK VRS or conventional Traverse from NGS or county Monuments. If you are one of those that either scale coordinates from a project location on your site do you change the false Northings and Eastings by adding or subtracting so that the Coordinates no longer look like State Plane. I see many peoples data that work off the same exact VRS network of others that in the raw direct observation will match but after either scaling them to ground no longer ties correctly. I understand why this is. My question is? If you as a professional have manipulated the coordinates to meet your states or your offices procedures and standards for whatever reason. Why leave them looking like State plane Coordinates. This causes confusion in my opinion and seems to be nothing but a little bit of laziness to not fix this. I went to a site several years ago to help a client that was trying to figure out how to use RTK for the first time. When I arrived he had the Site control from a previous Survey/Surveyor. I was teaching him how to perform a site calibration. Anyways the values looked like State plane. After much research and such we found the survey had been scaled/rotated and the incorrect units ie. UsFT vs International foot. Lots of issues. I asked him why he just didn’t lop off the false northing and easting so they looked like assumed coordinates and problem would have been solved. How are your office procedures for State Plane to Ground or vise verse? I have no problems with scaling but once you scale should it not be at least a report stating how it was scaled for example the new origin point and scale factor so it can be retraced? I prefer to work in grid and then perform either a LDP or a project scale factor to ground when necessary but I always make the values look different and still give a report of what I did so it can be reversed easily to get back to the known Datum. This is also the case for Site calibrations or localizations. Many ways to skin the cat and depending on manufacture software and hardware how it can be done. But it is to easy to change the values so they do not look like something they are not.
jitterboogie replied 2 years, 3 months ago 16 Members · 33 Replies- 33 Replies
A few thoughts on this…
Assigning motoves such as laziness adds nothing to the conversation. All you accomplish is to alienate and inflame a good portion of your audience.
It is very common to see georeferenced data overlaid on a survey long after it is done. Right or wrong, many allow the similarity in values to accommodate this practice.
From a personal perspective I see value in the various approaches. All require good habits in file naming and providing metadata. I have yet to see a coordinate burst from someones chest and scurry across the floor like a baby alien. Manage your data well and the problem is solved.
Taking the analogy another direction, I have never found a random coordinate laying by itself and assumed it fit for any purpose. Like a toddler finding a petrified cheerio in the seat of a minivan, if I choose to put it in my mouth I kind of deserve whatever happens. If I’m lucky I will make the connection before I happen on a cheerio with toxic mold.
In all seriousness, the debate on what is proper and what is not won’t end any time soon. I suppose the debate on how far we baby proof things is just as robust. As professionals we have a duty to meet the laws, rules, and standard of care. Manage your data, provide metadata, and watch that your engineers don’t pull anything out from under the car seat and put it in thier mouths.
All coordinates must have metadata to define what they mean. Looking like something is not adequate. With good metadata you can do whatever you want and someone else can transform them as they want.
I am in the camp that advocates subtracting off the high digits before or after scaling (and specifying which).
.I apologize for the word laziness. It was by no means to be meant the way I see you took it. I was with my poor choice of words trying to see how others handled this. When I was i. Colorado many years ago. Two sets of coordinates were published. And identified grid and ground. Metadata. I agree it doesn??t matter as long as it is documented. Its relative to itself in simple terms. I just see engineering files with what looks like spc and in reality they are ground or some hybrid without the metadata to support. As easy as software has made this it just see s so easy to place the metadata when many do not. Again I apologize I just wondered how others handled this workflow. I have consulted with many companies over the years when even they in there own offices because of management change etc. I just wondered if anyone practiced not making coordinates look like spc when they had been changed. The laziness comment i see was improper. Was not meant the way it sounded. After your comment it made me see that for sure. Thanks for pointing it out.
@olemanriver And I suppose I could have made my point more gracefully. This is an excellent and timely topic.
We are entering an era where a 4th dimension is needed with our data. If we do not get better at providing, maintaining, and demanding metadata things are going to get ugly (or uglier)…
Oh I am not offended at all. So no worries. Yes we have gone from taking ellipsoid distance to grid then ground to grid now grid to ground. One of the reasons I even started this thread was to get people thinking when we add Time velocity to the equation. The profession needs to step up and be prepared. Metadata or whatever catch phrase we want to call it needs to be available and concise. For sure! I love this stuff.
- Posted by: @olemanriver
Why leave them looking like State plane Coordinates. This causes confusion in my opinion and seems to be nothing but a little bit of laziness to not fix this.
I agree 100% that this is useless confusion and should not be continued. In my opinion, one should never ever scale coordinates. the CSF is to be applied only to distance. If you are going to be on ground coordinates, then the values should be way different than SPC and I suggest much smaller values like 10,000/15,000.
Laziness may not be the correct term. Perhaps incompetent.
in?úcom?úpe?útent- not having or showing the necessary skills to do something successfully.
Well I see I am not the only one who sees the confusion and lack of understanding or what you said. Or just neglect. I remember running geodetic traverses. We had to know which ellipsoid and lat long to get the mapping scale of each end of the line. We had to manually calculate k1 and k2 from clark or grs80 or wgs84 ellipsoid. Then apply that scale to get to the mapping projection UTM grid or SPC grid. Then we calculated the elevation or elevation/ellipsoid factor to get the CSF to take the ground distance that were corrected to grid distance. This was not difficult it was time consuming. We have software now that does a lot of this for us. Now scaling coordinates is just easy but you are correct its not technically sound but from a money and production stand point it is what it is. That??s really the place the rubber meets the road from my perspective MONEY and TIME and not have to think to much. I do unfortunately see way to many surveyors. Licensed down to the field crews that just want to push a button the same way no matter what. I was ruined I think early in my private side surveying career. I was quizzed on things like instruments specs angle accuracy edm accuracy single vs double compensators vs no compensator. I had to read the manual on my equipment and before I could become the I man i had to know and understand it. Reduce traverses at a minimum by compass rule with nothing but a calculator. Now we can perform least squares in the field at certain levels. How do we get ready for the future when we are ignoring the past and present. I am rambling know lol. Out feeding cows and trying to figure all of this out. Metadata needs to be addressed for sure at professional level. Then CEU needs to be more than just a check in the box. Yall out there who are more knowledgeable than I lets solve the problem and not just paste a bandaid on it.
Like others have said, Metadata is key. Explain what you have done. Scale, Rotate, Translate, how and why. How did you get the scale; OPUS, NGS datasheet, between two found points shot with total station. Rotate, to what and why; Basis of Bearings from a record map. Then my technique is to translate to new coordinates or as others have said truncate so they don’t look like State Plane coords. If you open one of my CAD dwgs and it’s at 50,000/50,000 you generally know I moved it. Check for layers named “survey notes” or “translate” etc. to find the metadata and connecting lines from 50k/50k to the original starting point. I also will rename the dwg to something that states what’s been done, “record of survey ground distance.dwg” “boundary survey rotated BOB.dwg”. Next up is doing the same to the fieldwork aspect. Rename the data collector files, possibly starting with a new txt file, and do what needs to be done, calibration or whatever.
I run lots of jobs in SPC for design, GIS, collaboration with others, or required standards, etc. But typically I want to put my record of survey boundary maps on ground distance and recorded map Basis of Bearings. CSF is typically around a foot per mile where I work and makes a significant difference on large boundaries both in distance and area calcs (for the real estate people). I had a company standard written up at one time. And sometimes you just scratch your head on what the data will be used for, and who will need the data, and will they understand your survey notes .
-JW
@j-dub I reckon I like what you are doing. I see some fight the metadata part. But what they did for years before GPS like assuming 5000/5000. Ran the boundary assumed north or held an adjoins plat bearing converted chains to feet. It was all noted ??metadata? I have no problem at all if someone chooses not to work on a know. Datum. I just think if you do the. State what you have done. With today??s technology I can literally easily go to a job step out of the truck drive a nail and grab GPS and do a one point calibration to an assumed 5000/5000 point walk a few hundred feet set a nail and record it. I now have based an assumed grid from lat long to 5000/5000 my north is good and I can grab my robot traverse meet the standards and a week later the client can request I place it on NAD 83 SPC zone whatever. I have everything I need to convert my little site datum to that now. Just a little math and build my transformation. It really is not difficult. GPS has made it so easy we complicate it. I like the approach of keeping everything on or tied to a known datum weather I publish it that way is not important what is is the metadata and keeping things not looking like they are not. Heck in reality I don??t need coordinates at all to perform a boundary or stake out or topo. They just make it easier. If I hung my shingle tomorrow I would take small jobs when I could and teach my people how to do things the old fashion way just so they would see the big picture. House topping on a line. Bucking in wiggling in. Traverses by deflection/lay out a road by occupation of cl point pc and pt . No coordinates allowed . I worked overseas while serving and worked with a guy that was doing layout on a base that I supplied all the geodetic control for. He and base general asked me to give him smaller coordinates. Not UTM to big of numbers. Once he told me what He needed. I provided him site coordinates from mine and scaled everything to the surface so he could perform layout correctly. Was about .25 per 1000 ft. That was going to cause problems. I wrote the report and all and he was happy. Many ways to skin this cat. Just have to state it so someone else can follow it.
I was working on a LARGE project. We were tasked with doing the property acquisition and Boundary Surveys. The CFS in this area is about 0.20′ per mile. The engineers were tasked with designing the project within the foot print that we acquired. All of our surveys were done in SPC GRID, and there is a note to this effect on each boundary exhibit map one of the Boundary crews crossed patches with a crew cstaking clearing limits from the contractor doing the construction the clearing crew told the boundary that their boundary was wrong come to find out, the engineers had scaled their SPC about a VRS station in the next county east thishas all the markings of a BIG Cluster you know what. Fortunately, they pulled the plug on the project and it hasn’t bitten anyone, YET. We surveyed over 600 parcels for nothing..the good news is that the surveyors got paid
I no longer live in the world of SPC. WGS 84 (G1762) all the time, in all that I do. I don’t miss these conversations.
I no longer live in the world of SPC. I live and work in Low Distortion Projection-land. Yes, In a perfect world people who scale SP would document their procedures better. Dream on. This debate will go on as long as SPC exist.
During my time in Oklahoma the typical procedure was to simply work in SPC. No scaling. I don’t have a big problem with that.
Here is an scenario I ran into. Company X goes out to a job. Takes rtk vrs shots on 3 points with correct spc chosen in data collector. Then imports those coordinates into scale factor 1.0000000 job only. Traverses etc. back at office the spc is scaled to ground while vrs station is still in the mix. They just randomly chose a point. No consideration for job site elevation from on side to the other etc. then all data i to drafting software. I now have 2 to 3 points that are the same just with different coordinates after they adjust traverse. I go out with not knowing all of this just to topo. Set up robot take bs +- .04 distance do a third point ck. distance .04 but left right.15. I start trying to figure out why. Well no documentation just the guy said oh that number is gps point the other is gps scaled the other is final traverse. I was like man this cluster made it to the field. This all was caused by not scale issues poor documentation and procedures. The company is causing there own inflicted wounds. There focuses is grid to ground. I say Lack of understanding maybe.
@steve-corley
Welcome back, Steve. It’s been too long.
If I convert to a ground based system I translate the project at a point I like to N10,000.000;E15,000.000
Rant on.
Friends don’t let fried scale to ground without truncating. If you need the project scaled to ground but still want to use georeferenced imagery, you can easily translate the imagery to fit the truncated coordinates.
Yes, meta data is a must. The problem is that it never seems to make it to the engineering plans.
Rant off.
In defense of DOT surveyors they are very well aware of problems caused by scaling and have been for several decades. We began using geodetic control in the late 80’s early 90’s with GPS deployment. Before that each project used assumed control, usually a 10k 10k origin on the project somewhere for total station only work. For the first decade or so the coordinates were scaled and truncated as is suggested in this post. But then the engineers started to design in CADD and use geographic overlay reference files. They insisted they needed survey on untruncated state plane but also needed coordinates scaled to ground for accurate quantities. (There is an argument just in itself) So the surveyors yielded to the demand and documented everything. Unfortunately those metadata documents never left the survey office and the plans went out with no indication the state plane looking coordinates were not. In our office this practice went on for about a decade until it was finally decided the metadata needed to be on the reference sheets. This practice went on for a few years with mixed results until it was realized there had to be a better way. There was a choice to make. Place every project on its own custom geographic projection with acceptable low distortion or develop zones for the state and promote the heck out of it in the industry. State geographic zones were developed and are now widely used by various county, city, state and private practice entities. It was mentioned coordinates should never be scaled, just distances. I agree however getting everyone on the same page with scaling distances on a large project with many involved is just as problematic as scaling coordinates imo.
Nice. I will have to say that I can completely understand why many choose a point and do what they call ground scale factor from one point. I can live with it even though we use to scale with the CSF our distance. Now if we want to scale from some point of origin a one spot we need to understand say how trimble is doing this. And we need to understand when it can make us exceed out standards. Say my site is fairly flat not a lot of elevation change. An lets say it this way averaged site/project csf we have truthfully created a new datum. But we can still work with this if we state what we did the new origin etc. and yes we can rubber sheet the imagery easy enough for the pretty picture for sure. Just truncate subtract or add so they no longer look like spc. I see where more counties require a tie on a boundary to spc. But the surveyor needs to calculate his boundary on ground in some places. Easy multiple ways to do this. Survey on spc with gps and total station draw everything and calculate the ground distance for boundary not hard and I believe most software will do this easy enough. Or give the county gis the lat long of those corners and work in ground. Its nad83. Somewhere along the lines we have got stuck in a vicious cycle of plane coordinates. I love them myself. But its to sasy now days to do multiple ways to get the right answer to Not document.
- Posted by: @stlsurveyor
I no longer live in the world of SPC. WGS 84 (G1762) all the time, in all that I do. I don’t miss these conversations.
How are you doing this? Other than the “here now” position there is nothing broadcasting WGS84 positions nor are there any WGS84 positions on monuments outside of some DoD installations. Of course the associated epoch of ITRF is available via OPUS, etc. and that is closely aligned to the corresponding WGS84 epoch. If you are pulling off an OPUS report the ITRF data and using that as a basis, then you really are using ITRF and NOT WGS84, although the difference is small.
Even if you are using ITRF or WGS84, then what are you using for a grid system?
The issue isn’t what underlying geodetic system you are using, either “WGS84”, ITRF, NAD83, etc., the issue is then getting grid coordinates on a non flat earth. You have the same issues no matter which geodetic system you use.
With rare exceptions, i.e. a DoD project where you may have access to WGS84 monuments, no surveyor should be reporting that the basis of survey is WGS84.
SHG
@norm Oregon DOT (ODOT) had a visionary chief of surveys, now retired who championed LDP’s because of the exact issue you mention. We now have something like 40+ zones covering the state. You can have a true geodetic based grid system with low distortion, no scaling, rotation, truncating; just use it as is. All the metadata and defining parameters are published and it works the same as a SPC zone in your favorite software, you just note the zone in your metadata on your survey. Everyone then can be on same page, no guessing about what was or wasn’t done.
SHG
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