@rover83 it’s to easy. . Had a manager say its not and he wanted ground always so he could see the difference in deed. Now i can tell you we are about.05’ per thousand foot and a 200’ foot distance between a couple pipes found in the ground that’s been there since 1950’s i am not worried about.05 anyway. But it was a lack of understanding . I need to come work for you but my wife would shoot me if i geo batch it anymore in my life.
Yep, that is slick. lat/lon to get ellipsoidal distance, ellipsoid height to get elevation factors and division to get ground. If it needs grid, it just uses PROJ or something similar to get the grid coordinates. It doesn't need to calculate a scale factor..
For Runway 05, I did this little single parallel Lambert LDP which should make grid and ground equal and have very small convergence angles within, maybe, the airports grounds.
Ellipsoid GRS80
NAD83(2010) This doesn't matter unless you mix entered coordinates
Central Parallel 46 36 30
Central Meridian 111 59 0.0
Scale Factor at Origin 1.000184
False Northing 25,000 meters
False Easting 100,000 meters
If you're so inclined, see how it works for Runway 05 and maybe between the PAC and two SACs on the grounds.
@mathteacher cad Trimble Business Center i can compute lines in grid or ground within the same project. I have no idea about other cad programs but have asked that question about civil 3d. I reckon one other issue is as land surveying property it’s important in some situations to make sure the acreage is computed at ground. So even at say a tenth of a foot per thousand feet around a large boundary between grid and ground that can add up. It is simple though to convert by the sq of the cf though. I like the question you ask. Does civil 3d or other cad packages always assume it’s ground or if a chosen projection is set is it now grid. I have asked several people and not one has been able to answer .
Does civil 3d or other cad packages always assume it’s ground or if a chosen projection is set is it now grid.
I don't know if Civil 3D will scale points and I suspect even if it had that capability you wouldn't find many or maybe even any surveyors that would use it for such a task.
I do know if you want to turn on the built in google earth imagery in Civil 3D you have to select a coordinate system, but I haven't looked into it any closer than that.
When were given a plat with a municipal or whatever coordinate system or LDP, we utilized the function to make sure what we're calculating out for staking or boundaries matches their canned/expected/GIS/etc data created by their coordinates and system.
the tell was if they don't match to what the scale factor calculation should be, you obviously didn't scale it or scale it properly.
fun times I've suffered these trials and tribulations. as have many of the others here
@jitterboogie So in civil 3d when i set my drawing properties and i choose nad83 state plane etc etc datum and all. Is my drawing now in grid is it using the parameters i set to work in that datum and projection or is it just for the geolaction background map. The reason i ask is i have been told 3 different things. One it matters like I can’t have a different state zone and have my coordinates from another state even though it shows ok in the background map. Because its in a grid mode. Others say it doesn’t matter at all. If thats the case and its one to one so ground unless I apply the scaling it doesn’t make since. But neither does scaling coordinates to ground and calling them spc either. So if its for a background then it makes it difficult for an engineer to design in grid projections with civil 3d unless they scale. Which makes me like TBC even more. Lol. I am so green with civil 3d it scare the heck out of me.
NAD83 is a datum, giving you vertical and horizontal coordinates that are ECEFbased essentially, (and I know I'm opening a huge gallon van of worms by saying anything) to give the best representation of the squashed eyeball spheroid we live on in our part of the world.
SPCS is the flat coordinate system that's used to tie down all the monument and boundaries to best fit our simple human brains, and
when you're applying the NAD83 to the SPCS you're essentially stretching it out and distorting it to gain the elevation and ECEF part.
You can create anything you want to using NAD83, WGS84(both are realized off of the GRS80 MODEL ) or just make OlanRiver's Datum or and coordinate system and tell C3D what you want it to do.
NAD83 is definitely not grid, as state plane is absolutely ot a datum. They're both constrained by the limits of what and where they were developed to be used in.
SPC central Illinois won't work for Colorado like NAD83 does nothing when you're in Kuwait.
When you're close enough in two states that the planar nature of SpC appear ok, the details up close are not ok, unless again your using UTM or something that's got a wider scope.
Scaling the data beginning with the raw points you'd bring them into the drawing and then apply the scale that you want the UCS or whatever you're working in to be constrained to,
so like if you collection is in just lat long(WGS84) you could scale or constrain that to your known parameters, that you'd have to have calculated and built prior to that process.
easy example is just bring in lat long points and scale them to NAD83. they'll move. they should, it's a different model and potential. I'll go find some of my older workflows that I used when I did this type of work and forward to you and we can discuss it with a bourbon.
Your depth of knowledge is far greater than mine and better built from your past. I'm sure of this.
I'm blathering and showing how much I forgot and don't know in my 1 big beer on board readers digest abridged version of a topic that is at least a few semesters of good discussion and 1000s of hours of direct work and trial and error.
It's been a few years since I've worked with LDPs. For the Runway 05 LDP, the three airport control points, DQ3133, DQ3134, and DQ3135 have distortions of 3.228 ppm, 2.087 ppm, and 1.096 ppm, respectively.
Here's a piece of the NGS Explorer map of the airport. The three black marks with inscribed white triangles are the PAC and two SACs.
I miss playing with the PAC and SACs and mostly the airplanes and the lack of traffic from automobiles.
getting to close a runway for maintenance and then building a great basis of bearings from the centerline of the runway for all future development was a fun experience. Using the data to build out the western side of the LDP we had been using and were planning for the 2022 process was super fun.
was even a neat moment when the white knight 2 overflew us on a ramp up for the Virgin space flight in 2021. bizarre to see it from afar and then realized what it was as it became recognizable and it's huge!
@jitterboogie well i don’t have enough time to figure out civil 3d. All i know is our template has pre set to nad 83 state plane zone x. Always set. I have opened drawings that had sudo spcs north east elevation that were scaled to ground in tbc. Then imported into civil 3d. So essentially ground but civil 3d is set to nad83 state plane x. This confuses my brain. Because i can assign state plane to nad83 harn nad 83 2011 etc or nad 27 which has a different ellipsoid than nad 83 grs80 and clark 1866 in my mind if i tell a software this is what this is then it should be doing everything in that and if that is the case for civil 3d then my 1000 ft line i draw at grid is not 1000 ft at ground but 1000.10 . If its just for the background image then i will know how to deal with it as whatever i draw is ground and i can compute either way i drafted some deeds all ground and when i brought it into the civil 3d project that was set to nad 83 2011 state plane zone x everyone of those distances changed so i went a bearing and dist of 250 ft in a generic cad file brought it in and those distances changed so minute it’s negligible but why my boss was like had did you draw a line to the thousandths of a foot i was like what he was checking my boundaries decisions from deed to my determination that and this thread got me to asking questions because i took my tbc project and it was all in grid spc nad 83 and i keyed in the deed by ground distances and it was perfect no charge really but i am a rookie with all this cad stuff so who knows
hell I'm behind you, I just work hard and fast and the failures pile up so far behind me I don't see them anymore.
we can do a zoom or teams and work up a few not what we're working on situations to disconnect from the familiar and exploit the tools with their processes and see how they work.
I think the fear of unknown is deeply ingrained in most people esp ones with assigned liability to the work they do.
rightly so.
but not learning to push your comfort zone limits your future and growth when the changes occur and they will.
@jitterboogie i might have to take you up on some civil 3d training. I am slow and not productive in that at all. I have one monitor for cad and one for google searching how to do this with civil 3d then calculator and notebook constantly calculating to check myself lol. But just the plane old drafting is a chore for me. I am researching civil 3d classes. I want to get better for sure. Just no time its all gotta be finished yesterday lol.
I'm just a barely competent end user of C3D. I can list 10 20 probaly 30 people here that are way ahead of me and my crap skills.
I will say this, getting into the game late, my best survey mentor imbued to me that I'll never get the depth of the 30 years of drafting I didnt have till now, and I shouldn't worry about becoming the best and most amazing drafter, there are drafters for that, and auto draw is pretty powerful.
However I need to be competent and understand how to get Into the drawing and understand what is going on and how to insure the data is being represented correctly and also how to make sure we're meeting the obligations we have with the clients and teams were working with both inside the organization and outside with stakeholders and the public.
No one can know it all, and be the best always evertime in every way in everything.
I know what I don't know. My GIS mentor taught me that and engaged me in the enjoying the uncomfortable part of not knowing something, so I could learn even more.
I'd be honored to work with you, and I'll be learning more about you and your knowledge too which will make me better for sure.
@jitterboogie I just pulled the data sheets on a airport pac sacs and other control today. Getting the Field package ready for my crews hitting the ground running monday morning. I finished up on a few weeks ago pac was gone from construction of new drainage ditches. Used the end of runway pk nails. For a easement survey that was changing. I wish i had a penny for how many hours of data i have processed on pac and sacs. I have set a lot as well. Everything was tied to them out to 7 nautical miles away. You haven’t lived till you drag raised an old humvee down an airstrip lol. Tower this is survey 1 plus 1 do we have the all clear to race. Survey 1 plus 1 get ready and go all clear.
If we're talking about SPC in Montana, the average geoid height (4 corners + 1 in the middle) is -13.72m (~ -45 feet) based upon NGS monuments.
In particular, if we're talking about Helena, MT airport, the average geoid height is -13.164m (~ -43 feet), per the FAA/NGS/etc. And the average orthometric height is 1,173.165m (3,849 feet), and average ellipsoid height is 1,159.999m (3,806 feet).
The point is that the ellipsoid and the ground are quite close to one another, which means the grid isn't that far off. (In Michigan,the geoid height is about -33 meters)
How does your math conclude that the grid is anywhere from 12,000 to 17,000 feet (2.75 miles (average)) below the ground/ellipsoid/whatever?
The most extreme cases will be in the mountains, but "nothing" is in the mountains, so there are very few instances of extreme elevations. Which is why they picked a single Lambert Conformal Projection for Montana.
The diagram you supplied is exaggerated only to show the concept, it is not "to scale".
You say:
Using TBC in a state plane projection I create two ground points using the create point function and bearing/distance.
Inversing the points, the resulting numbers are thus:
Grid distance: 2640.00'
Ellipsoid distance: 2641.57'
Ground distance: 2642.24'
A rough conversion-each 20' in elevation change creates 1PPM (it's closer to 21' but 20' allows a calc in your head number)
The grid scale factor for this line is 2640/2641.57 or 0.999406.
The elevation (ellipsoid) factor is 2641.57/2642.24 or 0.999746.
Combined factor 0.999406x0.999746=0.999152.
check that number by 2640/2642.24.
The compliment or site adjustment factor would be 1.000849 or in 1000' the grid will be .85' shorter than ground (850PPM).
In other words the grid at this location is 600PPM smaller than the ellipsoid height or 20x600=12,000' below the ellipsoid. At this location that would place the grid measurement 17,000' below ground surface which is about 5300' above sea level. This is an actual location that I've surveyed and no I didn't use state plane for the surveys.
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It will be a heavy lift to make state plane usable in higher elevation states.
I suppose it's worth an attempt but the scale of the problem will make it difficult.
There wasn't any real reason to restrict the new (NAD83) Montana zone to grid scales less than 1, but that's what they did. That zone is really nice south of the Montana border near the central meridian.
It's the same in other mountain states with TM zones. The grid scale is too severe. They need to be greater than 1 at the CM raising the surface. Why would we wish to survey thousands of feet below ground?
Locally there were always distance shifts from state plane going back at least to the 1960's. There was even a region wide number 1.0003 called Pryor that was used. A 1.0003 scale factor represents 300PPM or 3 feet in 10,000. Sometimes the statement is made that state plane was designed to get the user within 1:10,000, or 100PPM. I've never seen that inside any local zones. Get outside the zone and state plane can approach it. But then the rotations are large or you're in another state.
I began using LDP's early on with GPS since I could design my own projections.
I never cared about distances, those are easy to deal with in state plane, it's bearings that concern me, and the 2022 design will still have rotations, sometimes very large ones in Lambert zones.
If we're near the CM then use state plane, scale the distances to a surface near ground within 10PPM if possible, if far from the CM then it's an LDP, I don't see it changing much.
Eastern Montana, 4d rotations, not interested.
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Surveying the Helena area 15,000' below ground is what MSP is doing.
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I'll save you from the code. LOL
Rover's diagram gives an overview, however, the state plane grid is always shorter (lower) than
the ellipsoid height where I work.
This explains the Helena runway.
Of course we've always had grid and ground dimensions. Obviously back in the instrument days and always going forward. The problem is CAD programs don't work easily mixing the two. Labeling distances has always been a coordinate inverse.
Most of my work (subdivisions, small boundaries, DOT) is SPC bearings and ground distances within about 5PPM.
