Grid to Ground / Combined Scale Factor vs Light Squared
Richard is right on (again).
Working “in/on GRID” with a Total Station (or any other instrumentation) is just a matter of software capabilities (or limitations). Back in the late 70s/early 80s, we were doing this very thing using an HP41 and a paper field book (NAD27 of course).
This gets back to my recent comments (or ravings) about modern surveyors being “slaves” to the software that they have on hand. Most modern data collector software should have no problem working in SPC, UTM, or LDPs in real time.
Some of the more esoteric (but often non-trivial) issues encountered when running Total Stations on the Earth's surface (like deflections of the vertical, spherical excess, or terrestrial refraction), can usually be mitigated by good procedures, or ignored altogether on SMALL projects. Mileage of course varies, but a basic understanding of the principals involved, and the overall nature of the area in which you are working, will allow you to make the trivial/non-trivial determination from a position of knowledge of the probable effects thereof.
The MOST WIDESPREAD “errors” that I see made with Total Stations, is traversing around areas with significant vertical relief WITHOUT making the proper corrections for temperature and barometric conditions, AND/OR vertical convergency. Those of us who work in the more mountainous areas of CONUS cross the trivial/non-trivial threshold on things like this (and Helmert corrections to leveling), a LOT faster than those working in the “flat lands.”
Loyal
I agree. The factor used should be as precise as needed for the project size and distances between points will require. if a distance is as large as 10,000.1 feet a scale factor of 6 places will keep it that precise to one place behind the decimal.
Since you're don't have measure precision greater than that, you probably don't care about a few hundredths of a foot between friends.
When dealing with coordinates, however, you probably have a little more concern if one person uses a scale factor to 6 places and another to 9 places.
Look at a colorado csf of 0.999123 X 1,000,000.0 = 999,123.0 vs. 0.999123456 X 1,000,000.0 = 999,123.46. But that is a matter of using the same value as each other, and you are correct.
I return scale to nine (9) places as SOP, even if the trailing 3 are zeros.
I NEVER scale coordinates, UNLESS I am trying to figure out what someone else did, or the client NEEDS to maintain consistency in an ongoing project.
Loyal
Amen, Loyal.
If you scale coordinates, they aren't SPC any more. They are project coordinates, which is fine, so long as everybody knows they are such and the conversion is documented.
The best way to differentiate them from SPC is to subtract off the millions and hundred thousands so they look different from SPC. That does wonders for removing confusion. "There aught to be a law" requiring that 😉 (Not really, but should be taught as good practice)
Here's a link to the PowerPoint presentation I created when I presented this topic at Autodesk University:
http://www.ejsurveying.com/downloads/CustomCoordinateSystems.pptx
And here's a link to the paper I wrote a few years back on the subject:
http://www.ejsurveying.com/Articles/Working_with_Grid_Coordinates.pdf
I was bummed to see a 404 Page Not Found error when I followed these links. @sinc, Any chance you still have these files locally? Thanks.
Papers can be found via ??Resources? link on site??s home page.?ÿ
@geeoddmike Appreciate the reply.
hi, great site and good info, BUT
am new to the site and now a member and still can't find it on Resources, and can't find 'resources' or 'attachements'
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any help here or can someone please email the two pdf s ?!
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thanks !!!
joe
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I just stumbled across this thread. The links to the PowerPoint and the pdf no longer work. Is there any way that you could post another link to them?
I afraid that Sinc will be unable to comply. He has gone to his reward. But somebody must have these files.
Theo D. Lite
I just stumbled across this thread. The links to the PowerPoint and the pdf no longer work. Is there any way that you could post another link to them?
See the link directly above this post
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I don't have them close to hand, but they are worth tracking down. Sinc's comrades carry on the torch here: https://quuxsoft.com/contact/ . Very, very good people. Other good papers would be Michael Dennis's/Mark Armstrong's Oregon OCRS paper and Michael Dennis's appendix to the NGS guidelines for RTK use. Both of those papers touch on a lot of the same things.
Here in rainy South Louisiana the difference between ellipsoid height and orthometric height is on the order of 4.4 ppm
I just noticed that this "thread" started back in 2011, so here are some links to Shawn Billing's excellent articles from 2013:
Ground verses Grid Part 1
http://archive.amerisurv.com/PDF/TheAmericanSurveyor_Billings-GroundVersusGrid-LDPpart1_Vol10No9.pdf
Ground verses Grid Part 2
Some good stuff...(w/pictures)
Loyal
Thank you Loyal!
A simple reason to use ellipsoidal height is that it's the ellipsoid you're scaling to/from when calculating that factor. Otherwise you would be scaling to some other entity that is NOT your ellipsoid.?ÿ