@norm crawl before you walk. But today in reality it’s running before we have crawled. Just pick this point and hit this check box compute ground scale factor. You stated it very clearly. But i would add once you scale to the ground. Don’t leave them looking like the grid coordinates. Unless you have very well documented that.
Wouldn't is be better if everybody used NGS terminology?
It will be best when everybody uses NGS defined SPCS2022 as ground for most intents and purposes with few exceptions. The only reason grids were developed was for practical applications with no need to do ground conversions. Mostly highway engineering in the days of the steel tape and transit when the error of 1 part in 5000 was fine. As measurements became more precise the need to redefine usable grids for some of the same purposes as originally intended was realized along with new uses such as more accurate GIS base mapping and geo referenced imagery. Even (at the risk of heresy) boundary survey. Imagine surveyed boundaries and GIS property line layers on the same grid along with aerial imagery and engineering line work. It is totally counterproductive in today's world of sharing information to create a ground conversion that is not a true geo referenced system that is scaled away from a low distortion grid.
indeed.
I took a huge pay cut to work with a group that developed an LDP based upon the 2022 guidelines and even submitted the results and process to be accepted into the NGS program, and we were accepted. I loved that aspect of my low paying government job, and would like to get engaged with that again. I can guarantee it helped to grow my knowledge in not only survey but Geospatial and geodesy and definitely helped me pass the FS.
Learning and using the system is not a distraction, it's a necessity for the future.
It is totally counterproductive in today's world of sharing information to create a ground conversion that is not a true geo referenced system that is scaled away from a low distortion grid.
Amen.
What really grinds my gears is how many folks will apply the ground conversion (is it at the origin or a local point? makes a big difference in how many sig figures you need), truncate (or add if you're really into confusing people) coordinates, reverse engineer a projection (often employing some version of the "Affine Post Processor Map Projection" in C3D or ORD), publish the goofball projection, and then act as if this method of getting mediocre levels of distortion for a tiny project is somehow better than just...creating a low-distortion projection that doesn't require any hoop-jumping or screwing with coordinates, which also covers a far larger area and has lower average distortion.
It's just stupid. Develop a good projection from the start and use it. Don't ^$&% with things you don't understand.
Unfortunately from what I see, we're going to switch to SPCS2022 and the insanity will continue...
One of the biggest surprises encountered after development of LDP's in our state was not using them but how some licensed surveyors insist that the grid has to be converted to ground just because of the belief that grid can never be ground. Not everyone by any means. Any cartesian coordinate system is a model. Look at the diagram in this thread if do don't believe that. Some models are more accurate, but none are truth. The trick is finding a model that is good enough for practical use. About 100 years ago it was SPC. Now it should be SPCS 2022. Every instrument measurement is an estimate. Actually, a true ground coordinate system would always be draped on the ground wherever it is. What a mess that would be.
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.
@rover83 I was asked this question today. Will there be a different way to scale the new system to ground and how will we work with ground if it’s different. Will this make gps work go away. So I guess the insanity will continue. I tried explaining that instead of the projection at the ellipsoid it will be closer to the surface. So less distortions between grid and ground distances. But they will be grid coordinates and surveyors want ground coordinates not grid. We have to scale grid coordinates to ground. Somewhere somehow someone made grid this magically thing that we should only know about and not mess with and just use it only as a means to get to the ends.
Tell them it will be just like a new SPC but the combined scale factor is so close to 1 that you can ignore it.
On the problem of getting from the globe to the grid, please consider the attached ppt and let me know what you think.
Same for anyone else.
@bill93 . Even with our system today. 90% of what is done daily would not matter if we just left it on grid to begin with. We have become so intrigued with everything we do first thing to do is have a grid coordinates system for gps and a ground scaled system for robot work. Its all the same site. But we create this two system approach and file system to keep things separated except when we throw all the csv files in cad to draft. Then it doesn’t matter. I want to be like my 3rd grade teacher and have a yard stick and every time i see someone clicking the button to scale to ground just slap the knuckles. Maybe we should invent a app that shocks someone every time they do. I know there are situations and geographical areas that we need to do this. But most of the time its really not necessary. I have been told carlson can handle in the field correcting ground distances to grid as you work with robots trimble does this. I am sure leica can. Is there any software that doesn’t have all the parameters already loaded. If they use gnss surely all the information is there. You don’t have to type no numbers to work on the projection as far as i know. I just choose nad83 state zone and reduce distance to elev/ellipsoid and if no gps data use a average height to get started for cogo comps. But I usually start with gps so i have everything it needs. How did we get to the point of using one combined factor from one point and elevation to scale coordinates. On a site. Even when i am made to do this. I usually do computations to see the best average elevation of the site that makes the most mathematical sense. And if that causes issues i raise the flag and wave. This is worse distortion than leaving it alone. Then those scaled coordinates make it to a plat. Now someone will see that and try and find a corner thats not at that location to begin the survey from.
When I stated the issue for #1 I should have said projected to the globe in reference to the globe being the ground we walk on. I appreciate the ppt. It seems easy enough to understand. I've been involved in this so long I may not be the best person to ask. We've also attempted to explain this. See chapter 2 of LDP handbook
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.
As you have experienced, its possible to design an LDP to fit the need. It's unfortunate if SPCS2022 doesn't meet the need. The point is that it is possible to get users singing to the same sheet of music with some coordination. The first step is to get all users to agree what the threshold is for ppm error and design limits based on that guided by elevation change and other considerations. Perhaps in mountainous areas 150-200 ppm is a reasonable goal for most applications. If the stakeholders have a part in design parameters, the buy in is a lot more attainable.
158 ppm (1:6300) design error will handle 6000 ft + in elevation change. 20 ppm will only handle 800 ft.
@mightymoe do you place geodetic north on surveys or grid north where you are located.
It sounds like SPCS2022 will/would have worked, but they failed to make a separate zone for said area? I don't know. Or he isn't up to speed on their status/progress?
It seems as if the people most likely to criticize SPC/LDP are often times the ones that confuse everything about geodesy in the first place.
