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I see this all the time. On plays design everything. No meta data and I have done 10 different boundaries since 1st of the year. All state nad83(2011) grid. All distance ground in surveyors notes. Nothing and Eastings could be off from half a foot to many feet. Depending on where they scaled to ground from. Some do zero some a point on site. Thank goodness I don’t need coordinates to do a boundary. But I can’t imagine stating a coordinate that looks like state plane that has been scaled and putting it on a plat. Everyone should have just placed a lat and long instead of nothing and easting would have solved about half of the issues and the GIS folks could have used that to rubber sheet.
Understanding plane coordinates and plane projected coordinates is a class that should be taught.
You are getting way ahead. The original post if from somebody that works for a construction company as a a layout person. I’m sure that grid to ground and scaling factors are not within the realm of experience and there is still the possibility that the control values given to him are the problem.
I am somewhat familiar with grid-to-ground conversions on GPS, But I told the survey team onsite (that we paid for) that I need 4 control points for total station use with a scale factor of 1.00000
and I know they purposely do this because they want to do all the layout. They are a union company (nothing wrong with that) but they question me about my credibility saying you should hire a surveyor to do your layout and whether am I FAA licensed to do drone work that I do for them etc…
witch I have my part 107
- This reply was modified 3 months, 1 week ago by jmason702.
Thank you for all this info, it helps me build solid reasons to question them, I don’t want to blindly say you’re wrong or you are messing with me.
If you want to lay the plans on the ground, you have to scale the grid distances using the inverse of the scale factor and elevation factor.
I think this is the opposite – to go from grid to ground you multiply by the combined scale factor (CSF), not its inverse.
ddI just hit them up now, for local ground values, Thank you
Grid = Ground x (Scale Factor) x (Elevation Factor) = Ground x (Combined Factor)
Solve the equation for Ground:
Ground = Grid / (Combined Factor)
So, just to throw some more wrench in here, the control sheet says horizontal (bearing/distance) and vertical are per county record dwgs, but the coordinates shown are SPC NV East by GPS observation (I believe I saw that they are using 5700/Zephyr setup, so GPS only) that are set up over aerial targets the county set in 2019. It doesn’t say whether or not the county dwgs are SPC, which I’d doubt they are so I’d assume they’re ground (but pulling those county dwgs listed would be in order). Either way, If I start with, say, the southern GPS coordinate and run metes (record) NE to the easterly control point, I get a point that is over 10′ from the listed (grid) control coordinate. This is outside of a grid to ground conversion and by itself would imply that the aerial target(s) have moved, are large enough to be outside local control tolerances desired or were incorrectly logged (?).
Now if I continue from that point (the record metes coordinate) NW to the northerly control point I get a (record) coordinate about 1/16″ from the control coordinate shown. This may confirm that the 2nd control point is, to use an old surveying term, “out o’ whack”.
Either that or in my general lack of experience and occasional mind-slip, I’m completely wrong.
If anyone else here agrees, I’d hold off on doing any layout and copy/paste some of this to your surveyor with a hope that you don’t have to finish paying them until they can rectify this error – and provide you with either ground coordinates or ground metes between control. That’s what a contractor/developer pays them for. There’s no way they should expect a paying customer to go through SPC conversions with a question about GPS precisions to verify what they paid for.
ddThank you for your work!
Yes, we did find a 10′ bust on the easting of that coord. it was a typo on the plans, sweet you found it!
This all makes my head hurt. In the mid 2015 the County commissioned a control network presumably to capture data for tight topo control. They set and controlled a network of nice looking monuments all stamped up and used as flight targets. I presume they did a flight, collected data, and produced high accuracy mapping for future design projects.
The Project Coordinate System are Surface coordinates using US Feet. I’m not going to work out how they are derived but they seem to remove 26million feet from the northings and do some additional adjustment.
That process is SOP for many municipalities dating back well before any GPS or GIS showed up.
Fast forward “many years” to 2019 and a new project is designed eschewing the 2015 control and possibly the mapping with a new set of control. This control is on the Nevada Coordinate System NAD83(2011); the drawing states this. That’s your answer from the drawings you’ve showed us, this isn’t tied to the 2015 system, it’s something new done for this project.
Why the 2015 network and the associated mapping for this design job wasn’t used? Don’t know!!
Why use a system with 0.16′ per 1000′ shrinkage for this kind of build? Don’t know!!
Someone somewhere made that decision and you need to continue on with it as the project surveyor.
My suspicion is that there will be some interesting tweaks needed to “fit” the build to ground while the control is grid.
But maybe all the design took into account the 150 some PPM. Sure they did.
Yes, the 2019 control was not tied to the original control. It is confusing… and yes they took off 26 million on the original control, I’m not sure why.
But what I think is good, is all the N/E on the CAD files are GROUND cords. and the survey is shooting in control for us and they are doing it in GRID to confuse us. So I feel I’m good at shooting in points from CAD with a TS at a scale of 1.0000 But have to get the survey to put in control to local ground.
That’s my thoughts on this, do you agree?
For the other job on the same site, the points I shot in from CAD were all measured out by tape checks. and were good, that’s why I feel the N/E cords on CAD are ground-based. That and the points on CAD are the same as the points they give us on the contract drawings.
Removing the 26 million is often done, that dates back to the 1960’s at least. Now it’s not done for the reasons it was then, but it’s a simple way to delineate project control from grid control. The project control can be calculated using the transformation equations provided. I’ll let you figure out if the equations work.
I can’t speak to your cad drawings. I wouldn’t be the least surprised that all the buildings, pipes, parking areas, ect. are designed using ground distances.
Thank you MightyMo!
If you are surveying in ‘Nevada State Plane’ then you ARE NOT ‘on ground. NDOT uses a Las Vegas Valley Mean Combined Scale factor of 0.000177 to go from grid to ground (up). That equates to 0.168’ in your “950 feet”. This appears to be your issue. You are only in State Plane when you are on the grid. You cannot mix surface measurements with State Plane, you are either on the grid (State Plane) or not. I have no idea who you are working for, but this can be a MAJOR issue if you do not comprehend the difference between grid and ground.
Moe is spot on regarding truncating coordinates to make ground coordinates obviously distinguishable from true State Plane coordinates. If you are working on a construction site you had better be operating on ground. Plans in Clark County are required to contain a Ground Control Plan. Frequently they are only one sheet and should be amongst the first few sheets in the set. That sheet should contain local coordinates and if a scale factor was used to obtain ground distances from State Plane, it should be included on this sheet. Also, the coordinate base point for the scaling should be included. I have found this to be overlooked or not provided on several occasions and it is extremely annoying and unprofessional to neglect to provide it. I believe it reflects a lack of knowledge by those who do this dastardly deed. I like using a base scale point of North 0.0, East 0.0, for good reasons. Also any coordinate transformations such as truncating should be included as Moe suggested: Northing – 26,000,000.00 East -700,000.00.
All that nice control done in 2015, then someone comes along and sets up SPC and designs from that, but the design is ground (pretty sure), control is grid. SIGH!!!! (Push that button, get that number)
When facilities get large enough grid-ground becomes an issue. Designing 3000′ below ground is problematic. Most items like parking lots, roads, curb and gutter, pipes aren’t materially affected by 150ppm, but when there are big buildings, bridges, large structures, tight setbacks, it must get dicey, I’ve never built anything using state plane, we usually start around 250ppm and get larger scales, so no local engineer ever wanted to deal with that. I did have a railroad demand SP in central Montana at 750ppm, that was very interesting, it never got constructed since the project fell apart during the land acquisition phase.
Friends don’t let friends convert grid to ground without truncating.
P.s I miss the thumbs up options
For the 80th posting to this thread I’d like to crow about the low-distortion zones system in Oregon called the Oregon Coordinate Reference System (OCRS). These scaling issues just don’t exist when using the OCRS. Yet too many people insist on continuing to F’ around with scaling state plane. Arrrgh!
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