Why is scaling SPC still so prevalent in this day and age? Drives me nuts that this happens so often by engineering firms requesting our services AND no amount of logic or reasoning will convince them it is a bad idea, grrrr...
SHG
What kind of csf is involved?
Around here, it's between 90, and 110 ppm.
(spc, to ground)
This equates to 1/2 a foot in a mile.
If it were a large CSF, it might have some logic...
It'd be nice if I quit seeing: Basis of brg. "Derived from GPS, on July third, 2016". Like that meant anything!
I am working with a recent deed that has the bearings to the tenth of a second and the distances to one thousandth of a foot, but there grid tie coordinates are 650 feet off.
It drives me nuts too.
For a while, I would sub some RTK work to another guy instead of hiring someone full time.
Every time he would not turn anything in until I gave him my findings for the control points.
Then he would only submit his coordinate list and no raw data.
Of course all his work would fit my coordinate list exactly.
What I wanted was information based upon independent data without the expectation of agreeing exactly with my TS work in order to use for quality control.
Instead I got shrinkwrap information that I could have obtained myself.
I am very suspicious of anyone that will not provide their raw data, especially when they are working under my umbrella.
0.02
IMHO, the size of the CSF isn't important, it is the idea of FUBARing a good SPC.
If you want something where grid is approximately equal to ground distance then design a local system for that, all modern software can implement a TM projection, simple, and you do NOT end up trying to figure out down the road if something was truncated, scaled and if so where it was scaled (about a point or the origin, etc.).
In other words there is a much better way to get grid to approximate ground distances, but folks are so entrenched in methods from decades ago that they can't seem to grasp the pitfalls.
Like I said, my rant of the day, wished I could make the light go on for folks.
SHG
Ive used the same technique for the last 20 or so years. We make a custom projection for each township (or several if the distortions are small enough). The files are named to indicate what they are. A bread crumb trail of readme files accompanies each job. The field notes contain the equipment, settings and source for each piece of information.?ÿ
The ability to work completely in SPC simply isn't there for all types of work in every geographic area. I've become more tolerant of other techniques but will COME UNCORKED if you leave me guessing what you did.
Not to sound like a broken record, but if you must scale your SPC to APROXIMATE ground distances then truncate them. I can not tell you the number of times I have received data from a client that looks like SPC but is not and the meta data has long since left the building.
Friends don't let friends scale without truncating.
Rant off.
On the flip side, if my file name is 'job#-zone-ground' and comes with a readme you should be able to figure it out. If not then truncating, converting to hexadecimal international feet and multiplying by the julian date won't be enough to keep the user out of trouble...?ÿ
This "issue" comes up so often that I hesitate to even comment on it (AGAIN).
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BUT, here's my 2-bits (AGAIN):
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IF you wish to play in the SPC sandbox (or UTM for that matter), then go for it. There are plenty reasonable (even good) reasons to do so, BUT if that's what you want to do, then play by the rules (SPC ain't SPC if you dink with it).
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If you "must" screw with the numbers (coordinates, distances, whatever), then PLEASE leave some coherent bread-crumbs (metadata) for the next guy/gal to follow.
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It has always been my opinion, that if SPC/UTM GRID Distances (or bearings) don't work for your project, then WHY muddy the water with SPC/UTM in the first place?
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Loyal
Metadata for everything!?ÿ
I've been checking into a bunch of survey plats by one guy done in my sister's neighborhood to see what is around as a basis for someone to work with and who does good work.?ÿ My 3 OPUS solutions fit his distances well within 0.1 as SPC and would be tenths off as ground distances.
He didn't put anything on the plays to indicate they weren't ground.?ÿ Come on guy.
Loyal sez "It has always been my opinion, that if SPC/UTM GRID Distances (or bearings) don't work for your project, then WHY muddy the water with SPC/UTM in the first place?"
That right there is my issue, either use SPC or don't, if you don't want to use them I have no issue, create yourself a local TM projection that gets grid/ground approximately equal instead of screwing around with SPC in the first place, you actually can have a projection with local and geodetic coordinates which is far better than 10000/10000 local by a long shot.
SHG
The problem with meta data is that it never seems to come with the data. Just my experience in the nearly 30 years I've been doing this.
The problem with meta data is that it never seems to come with the data. Just my experience in the nearly 30 years I've been doing this.
Good point!
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That is often the case for me as well.?ÿ Unfortunately, that trend continues to this day, no matter what flavor of Coordinates is involved.
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Pretty sad state of affairs,
Loyal
But why mess with grid coordinates at all? Why do we insist on using 20th century methods when we all have 21st century software? We have known the world isn't flat for centuries now. The federal government has been surveying on the real surface of the earth since the 18th century. The private sector and state governments had a legitimate excuse for using flat earth approximations, and they served us well, but now what is the excuse?
in a word: AutoCAD
Flat Earth is a useful fiction, even today.
Your data collector works on a curved earth, Carlson works on a curved earth, Traverse PC works on a curved earth...If you let your software dictate how you survey you letting someone else override your professional control of your work.
Boundaries established and maintained under State laws are expressed in terms of a flat earth. Regulations are written and applied in the same way. While SPC is handy for various applications, the distortions can far exceed the standard of care when compared to a measured ground horizontal distance. It's hard enough to get Surveyors up to speed. I'm not going to tackle agencies and the general public.
Putting my projects on nominal grid bearing with a simple relationship to SPC has great value. I do it the way I do for a lot of reasons. If an end user has my coordinates and no metadata it's thier own fault. My coordinates do not burst out of somebodies chest and scurry across the floor in some bizarre alien remake. They get published with a map and or report. Should the two get separated the file name is all that is needed to figure out the basis of survey. It's not that hard.
Wouldn't a local geodetic system accomplish the same thing with no scaling to get to ground?
SHG
NAD83 is all that is needed. I have not yet seen a state that has regulations prohibiting boundaries from being reported geodeticaly. I do mine that way in a number of states.
State plane boundaries are much more rarely encountered than geodetic. The only State Plane boundaries I have seen are either DOT or created in the last ten years. Almost all of the non DOT boundaries have had me pretty confused because of misapplication or inssuficient met data .
Of course state plain can be done right, and I don't really object to its use if the practitioner understands what he is doing. I just don't see a reason to add complexity to our work.
Frankly, I don't have that much trouble with scaled coordinates. Mostly because we do so little work in this area with the RTK and so much with the TS. What bugs me is that so few states have defined Low Distortion Projections.