Kent, you write very detailed descriptions. You are very good at it. They go on for pages. Why it would be a burden to put just a few lines in there (the meta data for a LDP) kind of baffles me. It wouldn't me much more than a couple of ties for a corner marker.
I'm not sure what software you use, I think you have Trimble Business Center (might not use it). It will handle all this with ease. You can switch between LDP's or standard projections like changing your shirt.
> Why it would be a burden to put just a few lines in there (the meta data for a LDP) kind of baffles me.
Well, the problem that should be obvious is that it is much, much easier to deal with tracts that are all on the exact same bearing basis and the same coordinate system (subject to only minor offsets from small changes over time). The alternative that Custom Projections needlessly generate is having to screw around with every description to put them on one single projection. That burns up time as the number of adjoining tracts multiplies.
Why not start with one projection in the first place? No brainer, particularly considering that the SPCS is so well known. I realize that if engineers or architects are involved, then they need to be fed coordinates in a system in which SF=1.00000+/-, but why clutter up the public records with that for strictly cadastral work?
One reason to do LDP's is when working on a large projects that cross into multiple state plane projections. I have two adjoining projects that are on two state plane projections that I wish I had made into one LDP. They ending up merging together and crossing each other.
I put them both on the state plane that they were in because I thought the company I was working for would like state plane. Turns out they wanted everything in UTM metric and I'm not going to work in UTM metric so I might as well have put everything in my own LDP. The west project pushed east, the east project pushed west crossing into each other and they both moved north into a third projection.
A LDP would have worked great for the whole area. I got a few calls where they merged and was asked why the bearings were 2 degrees different on plats for the same section. I told them to look at the basis of bearings statement.
Good point for one size doesn't fit all, although if the client insisted on SPC, I would of only used a single zone, no harm in that (unless you were covering an extremely large geographic area and then maybe the UTM would be better 🙂 ), the scale factors and convergence might be larger than "normal", BUT the math still works. SPC zones usually follow political boundaries, the zone doesn't quit working just because you cross a political boundary line. In Oregon when we designed the LDP zones, we didn't say you can only use this zone here and not there, in other words there is no designated boundary by County lines, etc.. General though you would want to use the zone for the area you are working in however.
Your point is well taken that the professional should be deciding what is the most suitable coordinate system to represent a project, might be LDP, might be SPC, might be UTM, might be something else.
SHG
> In my opinion, the codification of projection parameters by statute is the superior option. Anything that a DOT or the NGS maintains won't really be permanently archived for the obvious reasons.
Exactly what Oregon has done right in the Oregon Adminstrative Rules
SHG
> One reason to do LDP's is when working on a large projects that cross into multiple state plane projections. I have two adjoining projects that are on two state plane projections that I wish I had made into one LDP.
Sure, as I said, when you're working with engineers and geologists, there isn't any reason not to use a custom projection. However, when you're reporting cadastral results, custom projections come with the significant and obvious overhead I mentioned and should in my opinion be avoided in favor of standard projections.
> LDP's, fortunately, are often published by states and counties, in pdf. check out some of these, Cochise County AZ, all of Wisconsin, all of Oregon (thanks to shelby and others). At least that would possibly account for any mylar smudges. include your metadata, but you could also reference a publication.
>
Here is a link to the Oregon Adminstrative Rules where ALL systems are shown, NAD27, NAD83 and the OCRS.
SHG
Once your data is entered into a geodetic data base (lat, long & Height or ECEF X, Y & Z) you have every projection at you fingertips. I can convert my projects done in an LDP to SPC's with just a few keystrokes. I can give them UTM's, custom LDP's, what ever the GIS wants. I just don't see it as any big deal but you must keep your Geodetic Coords aligned properly with the world.
It would cause some irritation if all I had to start with was the SPC's as I would need to cook up the elevations but you could back out the CSF and then update with data collected in the field. But once your database in the software is loaded its pretty easy from there.
But each to his own there are lots of ways to skin a cat.
Since the PLSS was based upon north everywhere I find it better to align with north and not a SPC. As you get away from the central meridian in a SPC the angle just gets too big and causes all kinds of rotation issues. At least with a local LDP you are only dealing with how far from north the original survey was. All my cadastral projects descriptions originated from a system where north was north and the distance was measured on the ground. With LDP's I can do the math of a round world on a flat surface similar to how the original surveys where done. It sure works for me and I did use SPC for years just got sick of the conversion and rotation all the time and I'm usually above 6000 feet elevation so there is a lot of difference between grid and ground.
If total standardization is the best route maybe there should just be one projection for the US.
> Here is a link to the Oregon Adminstrative Rules where ALL systems are shown, NAD27, NAD83 and the OCRS.
It's a bit odd that the Oregon Coordinate Reference System Zones aren't defined as to extent, but I trust that the place names used in the projection parameters provide that clue.
> The rest of the report is just showing my work, which wouldn't necessarily need to accompany every plat or description I prepared using the projection.
Well, as long as you're including all of the metadata for the custom projection, on every map and written description you generate, at least future surveyors will be able to unravel what you've done and put it on a standard projection.
The zone names do in fact point to the primary area of applicability of each zone. If you look at the maps here you can see however that in some cases a particular zone may provide very low distortion well into another zone.
SHG
However, when you're reporting cadastral results
cadastral is one reason to NOT work in state plane. 2 or 3 degrees rotation in state plane systems with distances 2-8 inches short in 1000' preclude me doing many cadastral jobs in state plane.
LDP's are much better for cadastral work. But then I'm in the PLSS and everything was done "true north".....more or less.
> cadastral is one reason to NOT work in state plane. 2 or 3 degrees rotation in state plane systems with distances 2-8 inches short in 1000' preclude me doing many cadastral jobs in state plane.
Well, it hasn't bothered me for the twenty years or so I've been using the SPCS for cadastral work. I'd imagine in PLSSia each section or township is more or less its own little world, so you don't really have to worry about the large-scale connections between boundaries that Texas surveying touches on. While the value of a "Northish" coordinate system (one oriented within less than ten minutes of geodetic North seems minimal to me - you still have to convert grid to true - I'm sure it's helpful for generating approximate search coordinates if you haven't done so in the office already and don't want to be thinking about mapping angles in the field.
Isn't this exactly what Minnesota did for each and every county? (Twenty years ago?) The Republic of Colombia has done this for many of their city surveys courtesy of the Instituto Augustin Codazzi (The national mapping agency).
While the value of a "Northish" coordinate system (one oriented within less than ten minutes of geodetic North seems minimal to me - you still have to convert grid to true - I'm sure it's helpful for generating approximate search coordinates if you haven't done so in the office already and don't want to be thinking about mapping angles in the field.
"Northish" is a good description for many of the old surveys. Often times being "close" to true north holds little value.
And don't get me wrong I use state plane for many projects and it's often the best answer, but LDP's have their place also and not just for small areas.
All projections are going to have issues: I suppose a true north-surface distance system will be the real answer.
> Perhaps an affidavit filed at the county clerk's office could alleviate this? Not sure if this would work, just a thought off the top of my head.
Well, let's think that one through. You pull a copy of a deed and are back at your office trying to figure out where one corner tied in the description is on the ground. The deed says "bearings refer to Billings Grid North as defined in that certain affidavit executed by Shawn Billings ten years ago on file in the East Texas County Real Property Records in Book _____ at Page _______." How is that really very useful at all?
> Well, there's no difficulty in reporting surface distances in the SPCS as long as they are all computed using the same Combined Scale Factor.
>
First you complain because my calls for bearings and distances don't agree with the inverses from the State Plane Coordinates and then you give consent to scaling distances to make up for the Grid vs. horizontal/surface distance issue. I'm having a hard time keeping up with your complaint. If the distances are modified, what's the matter with modifying the bearings as well (so long as the proper metadata is given).
> It sounds to me as if you have never gone through the exercise of trying to put quite a number of tracts on the same projection. Having to deal with as many different projections is a major waste of time. The rational alternative is to put them all on the same projection. Once a standard county projection is adopted and published, I see no reason not to use it. However, following your desire to keep mapping angles as small as possible (for a reason that doesn't make any surveying sense, particularly), you will still be wanting to create a custom projection for every tract.
>
Actually I do this all the time. Creating a local projection for an area actually makes the process easier. I'm not sure where you got the idea that every job is on it's own projection. I create "neighborhood" projections.
> I'm afraid that doesn't make any sense at all. There is no difficulty at all combining conventional survey measurements with the SPCS.
>
If there really was no difficulty in combining survey measurements with SPCS, there wouldn't be so many confused surveyors asking questions about Grid vs. Ground (sic) and creating qsuedo SPCS coordinate systems. When I work with a local projection, I don't worry about scale factors at all. You do. Which sounds simpler? At any moment, I can give you the coordinates of any point in any projection or system you want.
> I don't think you probably do if you've never had the experience of being able to lift the coordinates of some distant corner directly from a metes and bounds description or map without basically recomputing the entire survey from which it was taken. This is fundamental to work with large tracts and many original land grants. The custom projection are really more one-off deals for engineering projects and tiny parcels.
Why not simply publish the lat/long of all of those points you would typically describe with SPC? I'm not so sure that I would publish plane coordinates from my LDP anyway.
> First you complain because my calls for bearings and distances don't agree with the inverses from the State Plane Coordinates and then you give consent to scaling distances to make up for the Grid vs. horizontal/surface distance issue. I'm having a hard time keeping up with your complaint. If the distances are modified, what's the matter with modifying the bearings as well (so long as the proper metadata is given).
Well, reporting bearings and distances that are grid distances divided by an average project Combined Scale Factor is a long established practice. Same thing with area computations. I've done this forever. HOWEVER, you report the actual SPCS coordinates upon which those inverses were based because the geodetic positions can be computed from them directly via standard projection (i.e. SPCS parameters).
> > It sounds to me as if you have never gone through the exercise of trying to put quite a number of tracts on the same projection.
>
> Actually I do this [trying to put quite a number of tracts on the same projection] all the time. Creating a local projection for an area actually makes the process easier. I'm not sure where you got the idea that every job is on it's own projection. I create "neighborhood" projections.
Well, that is completely illogical. Your objective in using custom projections is to minimize the mapping angle at all costs, so that means every tract ought to have the central meridian of the projection run right through it. That was how they did it in the future until they realized it would be cooler to shift the central meridian East or West to make the grid bearings match the record bearings as closely as possible.
> If there really was no difficulty in combining survey measurements with SPCS, there wouldn't be so many confused surveyors asking questions about Grid vs. Ground (sic) and creating qsuedo SPCS coordinate systems. When I work with a local projection, I don't worry about scale factors at all.
Well, that's an important thing you've overlooked. Just because East Texas is low and flat doesn't mean that the rest of Texas is. It isn't. So the Elevation scale factor has to be taken into account.
> Why not simply publish the lat/long of all of those points you would typically describe with SPC?
Well, the obvious reason is that it isn't necessary if you're using the SPCS. That's the entire point: standard projections are informationally efficient in a way that custom projections never, ever will be.
Kent believes lat and long are a derivative of SPC's, that geodetic coordinates come from the projection. Those of us that work with RTK and have as our base data the lat, long & Ht (ECEF X, Y & Z) realize that the grid (projection) coordinates come from projecting the points onto the Grid (SPC in Kent’s world) plane.
If you are a flatland surveyor that basically uses flatland (conventional) instruments this is understandable. The third dimension is expressed by a combined scale factor instead of the actual elevation or height. The SPC's were intended to be 2D systems. We've moved on to a 3D or even 4D world. The base values are ECEF 3D Cartesian coordinates. We can make our measurements and keep our data in this fashion. It's all computed from there (projected onto a flatland type plane).
The systems being implemented to map the world and provide data are 3D. Converting the 3D data to a SPC is easy. It's not so easy to go from a 2D to 3D especially if you must estimate the elevation via a CSF (or take it off a Quad map). It's like well, just fake it (estimate the elevation). If you have the actual 3D data you can get the actual ground distance if you need it.
A SPC with a CSF is just a form of a LDP without all the benefits. You don't have the actual 3D data which opens up the whole system to easily look at your data in any fashion you choose (SPC, LDP, UTM etc).
It's just groundhog day again.
