A thread below extolling the merits of custom projections to generate coordinate systems oriented Northish or (presumably) Record Northish led me to borrow my neighbor's time machine to visit the alternate future that would include them. I wanted to see whether it was mostly a bug or a feature.
In this future, every surveyor created a custom projection for every parcel that he or she surveyed, the object being to make the bearings of lines as reported match the bearings of lines described in the instrument of record that created the boundary. Apparently, in the future land title insurance companies will send out teams of their representatives to harass surveyors who report the actual directions of lines, so after some ugly incidents, most surveyors decided that custom projections were the way to go. The land title insurers were happy and everything seemed cool while the deed records filled up with metes and bounds descriptions, each based upon a unique map projection.
There was some initial difficulty but one prolific firm realized that they were going to be generating thousands of different projections and to keep better track of them they adopted a naming convention incorporating (a) the project name, (b) the date the projection was created, and (c) whether they'd been paid for the job. This was widely copied.
When the objection was raised that the distances reported didn't match the record as well as the title insurer expected them to, a custom scale factor was introduced that would produce grid distances that on the whole didn't seem very far off those reported in the deed records from a prior survey of the tract.
After a while, surveyors discovered that it was a neat idea to keep the parameters of their custom projections secret. After all, if any other surveyor wanted to know the latitude and longitude of a particular corner, he or she could just go out and survey it, right?
Unfortunately, the meter on the time machine was running out, but I could see that things were looking ugly, so I didn't stick around to watch the whole spectacle played out.
Thanks Kent, just got in and saw this.
I gave our son when he was 6, a copy of Marveltown inscribed to him from me for Christmas 2008. It is one of his favorites.
I need to view this later.
What is happening and will take over is GIS. The GIS will be loaded (eventually) with hard geodetic coordinates (Lat, Long and Ht or ECEF X, Y & Z). From there it's just a few clicks to any projection you want. They are already working on it (at least in my state). I get a few bucks every year for providing geodetic coordinates on PLSS corners. Soon every survey will be required to be tied to at least two of these corners, so we are getting there.
> I get a few bucks every year for providing geodetic coordinates on PLSS corners. Soon every survey will be required to be tied to at least two of these corners, so we are getting there.
Yes, that was what they said in the future also. :>
Sounds like full circle to the El Paso homeboy "projection".
wow. humbling that my little suggestion unnerves you so. perhaps the future also has support groups for surveyors with unhealthy dependencies on a single method of expressing geographic coordinates. lol.
Actually, I'm not bothered by your disagreement with my suggestion that Low Distortion Projections might also be effective at diminishing the trauma of moving coordinates, as well as being a fantastic bridge between ECEF GPS determined positions and terrestrial measurements. (Even if you really haven't addressed the theme of my post below). I appreciate the challenge. Adopting new methodologies requires careful, honest consideration before implementation. The questions you are raising are helpful.
> Sounds like full circle to the El Paso homeboy "projection".
Actually, I thought about plugging the coordinates of El Paso into the time machine's controller, but it turned out they were secret.
> Actually, I'm not bothered by your disagreement with my suggestion that Low Distortion Projections might also be effective at diminishing the trauma of moving coordinates, as well as being a fantastic bridge between ECEF GPS determined positions and terrestrial measurements.
Okay, that last bit is just strange. You realize that if you have NAD83 SPCS coordinates and ellipsoid height for a point, you can compute its NAD83 ECEF coordinates, right? Yes, you can.
I wonder if you mean that custom projections can be a wonderful workaround to actually understanding anything at all about geodesy? In the future, that was considered a big deal.
you have to make more steps to convert your measurements to SPC than I do to convert my measurements to LDP, which is zero.
My LDP can be redesigned with new origin parameters to accommodate translations from readjustments or datums. CAD work and coordinate lists remain unchanged, only the projection that defines them changes slightly.
Strange, huh?
> Strange, huh?
Yes, this was something that Bill Strange mentioned years ago as a workaround for those surveyors who were dead set on coordinates of boundary corners never changing even as their NAD83 positions did.
At the time, it seemed to be something possibly more useful on the Pacific plate than in Texas. In Texas, it's more like a solution in search of a problem.
If you look at a map of Texas, you'll see considerably more variation in elevation than exists in East Texas, which is basically flat and where one may entertain the idea that the variation in Height Scale Facorts doesn't really matter. Even in Oregon, the fiction their LDP's require is that mapping will be along highways, not actual terrain to either side of the highway.
> Even in Oregon, the fiction their LDP's require is that mapping will be along highways, not actual terrain to either side of the highway.
Hate to be the one to break it to you Kent, BUT there is a reason for the zones being designed like that, no myth or fiction to it at all, actually a couple of reasons:
#1, the ODOT was a chief proponent of the LDP's to get away from the bastardized systems that had been being used, you know the type where SPC are scaled to ground and then are worse than a 10000/10000 system.
#2, this turns out to be a good thing actually, because there really isn't a high demand for surveyors outside of the transportation corridors, the entire SE portion of the state which has no LDP zones and probably never will doesn't have any people living there either, so in the end, I would guess the transportation corridors and their corresponding LDP's cover about 90% of the population of Oregon.
Do surveys actually get done places in Texas that have no state highway corridors nearby? I know things may not be advanced quite as far as Oregon in Texas, but heck, maybe even a gravel state highway or something must be nearby to access the lands in that great state.
There is at least one state highway in Oregon, actually right here in the part of the state where I live that is gravel for a portion of the route, probably will remain that way for a good long while, so no, I am not joking about a gravel state highway in Texas.
SHG
> >
> In this future, every surveyor created a custom projection for every parcel that he or she surveyed, the object being to make the bearings of lines as reported match the bearings of lines described in the instrument of record that created the boundary. Apparently, in the future land title insurance companies will send out teams of their representatives to harass surveyors who report the actual directions of lines, so after some ugly incidents, most surveyors decided that custom projections were the way to go. >
> There was some initial difficulty but one prolific firm realized that they were going to be generating thousands of different projections and to keep better track of them they adopted a naming convention incorporating (a) the project name, (b) the date the projection was created, and (c) whether they'd been paid for the job. This was widely copied.
>
Kent,
are you saying LDP's don't work?
the point is (if you read up on LDP's as many of us are learning) is the intent is not to develop LDP parameters for every single project. i have to hit the field soon, but will assemble some things for you to read about LDP's merits.
in an LDP, you move the projection to at, or near the ellipsoid. doing this makes your ground distances so near identical to grid that it is almost trivial. the INTENT of LDP is to create a zone, NOT a project. granted, the zone's distortions are governed by topographic relief and the zone's dimensions. Another intent of LDP is that we have gear to measure with much greater accuracy than we could when state grid was developed and published. the idea is to model and publish in a similar precision. rant off, on with the Kent show...
Shelby
I've literally surveyed hundreds of thousands of acres that had no access to a highway, but probably one little dirt road in and out.
No, he didn't say they didn't work. He just acknowledged that they did based on Mr. G's recommendation that they may have an applicable status.
No, what he really said is that it's stupid to him, therefore it's stupid period and not worth the time and effort to disprove it.
Sometimes you have to read between the lines with Kent, and when you do, think about the argument acumen of a 5th grader and incorporate that for explanation and use it as a secret decoder ring. 🙂
> > Even in Oregon, the fiction their LDP's require is that mapping will be along highways, not actual terrain to either side of the highway.
>
> Hate to be the one to break it to you Kent, BUT there is a reason for the zones being designed like that, no myth or fiction to it at all, actually a couple of reasons:
Well, that was my point, Shelby, that the Oregon LDP's work for the highways that have much less topographic variation than the land beyond their routes. This is an important point because to be useful for cadastral purposes a projection has to cover it all, not just the flat lands.
> are you saying LDP's don't work?
No, obviously not. The point that should be amazingly freaking obvious (but apparently isn't) is that the proliferation of map projections defeats the entire purpose of using them in the first place, i.e. to be able to map geographic positions in a system of cartesian coordinates. In Texas or anywhere that cadastral surveying involves knowing something about the larger pattern of lands outside the limits of some subject tract, it isn't just some theoretical objection but one with real implications.
As projections proliferate, each little mapping grid has its own bearing basis. Strike One. As projections proliferate, the difficulty of readily determining the relationships of tracts and parcels increases hugely. Strike Two. Apparently, the main reason for being enthusiastic about Custom Projections is that the user doesn't have to know anything about geodetic surveying. Strike Three for cadastral surveying.
> Another intent of LDP is that we have gear to measure with much greater accuracy than we could when state grid was developed and published. the idea is to model and publish in a similar precision.
That makes no sense at all considering that it's possible to compute a survey on a projection of the SPCS at millimeter accuracy. That is, the projection equations between geographic and grid coordinates work. So claiming some sort of accuracy advantage for Custom Projections makes no sense unless you want to pretend that a survey was made in a local coordinate system with SF=1.000000000 and not take into account the change in scale factors over a large area when the survey is computed.
The genius of SPCS was apparent in the industrial era. In the technology era we find ourselves in today, they seem out of date. If anyone is doing any time travel to find the virtues of SPCS over LDP, it is you, Kent. Only you are traveling back in time instead of enjoying the progress available to us today. Large scale factors coupled with mapping angles that exceed the error potential of a modest compass, were justifiable in the days when surveyors were calculating geodetic positions from terrestrial traverse by hand. These inconveniences were outweighed by the ability to use tables and simple arithmetic to solve positioning computations. Today they are simply unnecessary. Obviously today's technology is "backwards compatible" to suit those who simply don't want to follow the forward trend, so working with a survey published with SPC's will be no real inconvenience to future practitioners, but for those forward thinkers and particularly the pioneers who have been doing this for decades, the rewards are pretty evident. The real question isn't whether LDP's are superior to SPCS, quite evidently they are. Your only substantial complaint is that of documentation of the LDP parameters. However, even you have been unable to discredit the actual implementation of LDP's, regardless of how "freeking obvious" you claim the opposite to be. Certainly, you must be able to recognize that a system with distortions of 5ppm (or less) is better than one with 100ppm (or more). Certainly, you should be able to see that three arc minutes is less than 3 degrees.
> The genius of SPCS was apparent in the industrial era. In the technology era we find ourselves in today, they seem out of date. If anyone is doing any time travel to find the virtues of SPCS over LDP, it is you, Kent. Only you are traveling back in time instead of enjoying the progress available to us today. Large scale factors coupled with mapping angles that exceed the error potential of a modest compass, were justifiable in the days when surveyors were calculating geodetic positions from terrestrial traverse by hand. These inconveniences were outweighed by the ability to use tables and simple arithmetic to solve positioning computations. Today they are simply unnecessary. Obviously today's technology is "backwards compatible" to suit those who simply don't want to follow the forward trend, so working with a survey published with SPC's will be no real inconvenience to future practitioners, but for those forward thinkers and particularly the pioneers who have been doing this for decades, the rewards are pretty evident. The real question isn't whether LDP's are superior to SPCS, quite evidently they are. Your only substantial complaint is that of documentation of the LDP parameters. However, even you have been unable to discredit the actual implementation of LDP's, regardless of how "freeking obvious" you claim the opposite to be. Certainly, you must be able to recognize that a system with distortions of 5ppm (or less) is better than one with 100ppm (or more). Certainly, you should be able to see that three arc minutes is less than 3 degrees.
While I agree mostly with you, there is much to be said for mapping angles of large numbers. In SPC environment, approaching central meridians plays hell with discerning of data because we grow acustom to not looking at the signs much. I have one project that sucks because sometimes, you turn left to true.
That being said, the 3' of arc could very well mess with someones head much like assuming an elevation close for a topo and not saying it's assumed. It doesn't make the work inferior, but can cause problems. Not as much with 3' as with hundreds of feet and some idiot not using onsite benchmarks.
However, with the proper metadata, and I know you make it available, people will continue to screw up train wrecks regardless of what you put out there. 🙂
All true Kris. I was waxing on a bit with the superiority of LDP over SPCS. They both have a place.
You mention people creating train wrecks... I never thought much about it until I asked the question yesterday. It is funny, the questions that immediately come to mind when I see a plat with SPC's or worse, a CAD drawing in SPC's. I'm immediately wondering if these are real SPC's or someone's bastardized rendition of SPC's. It's been the latter enough to make me dubious most of the time, unless it's from a trusted source. Now obviously if I saw a plat with UTM coordinates on it or Lat Long, I'd have questions about that too. But they wouldn't be the same questions. I'd likely wonder if they were based on someone's consumer GPS device or a tighter control, like CORS or HARN, etc. But I probably wouldn't worry too much about whether the UTM coordinates were scale at the origin, I certainly wouldn't worry about that with LLH. Unfortunately, the death (or considerable unhealthiness) of SPC's is as much caused by neglect and the slow, brutal, bludgeoning of ignorance from practitioners as any technological advancement.
Of course, LDP's aren't immune from the same misuse SPC's have suffered, but the motivation isn't there. People eff up SPC's in a lazy attempt to compensate for the distortions (primarily scale factor) inherent in the SPCS. With LDP's this has already been accounted for. Not to say people won't still find some way to screw them up, but it'll be more from ignorance than malice.
> Large scale factors coupled with mapping angles that exceed the error potential of a modest compass, were justifiable in the days when surveyors were calculating geodetic positions from terrestrial traverse by hand.
Okay, you're surveying with COMPASSES in East Texas? Why didn't you say so in the first place? This whole discussion is about map projections and why the unnecessary proliferation of them defeats the larger purposes of map projections in the first place.
> However, even you have been unable to discredit the actual implementation of LDP's, regardless of how "freeking obvious" you claim the opposite to be.
I have to wonder what sort of a weird and wacky world you're working in. It's obvious to me that having every survey oriented to a grid that sort of resembles geodetic North, but really isn't is backwards into the 1950's. In modern times, it is extremely useful to have all surveys referenced to a common bearing basis. If that isn't obvious, you are way behind the curve.
Likewise, as Kris pointed out, having the mapping angle change sign across a project is dumb. The supposed disadvantage to mapping angles larger than the "error potential" of your compass is actually a good thing.
