> Just let the RTK controller figure it out.
>
>
> What do I win?
You may have just won a McDonald's Happy Meal (if the RTK controller can give you directions to the outlet nearest you).
> By low I believe he is talking about a bit lower in elevation so the .999863 CSF would be a bit "lower" than the .999861 CSF. But really these are just number games at that point, if I was in a valley surrounded by hills I would skew towards the "higher" number, by the same token if I was surveying along a ridge I would go with the "lower" or larger number.
Yes, that's also the approach I use. The entire survey of control points may contain a few outliers that can be overlooked. For example, there is the station designated as 1Day297 with the largest CSF on the project.
Actually, 1Day297 was just a pretty good spot to leave a GPS receiver for the afternoon to get a connection to NAD83 via OPUS-S while I was working on a ridge above it. It won't be shown on the map or mentioned in the written description and so will be invisible in that sense.
Whether you use some state sized projection or an LDP is a matter of whether you want your plotted results to be near reality (ground distance and "north") or some distance you can't touch (SPC grid) skewed from north to the pole. With SPC's you can do some math (apply a factor) to reveal the truth.
I choose to do it the other way, use an LDP (near the truth) and supply the LDP projection info for those to use out of the box and also to convert to some other larger scale projection like SPC or UTM IF they have the need. As long as the coordinates supplied (or being able to back compute) are true world coordinates (NAD83, ITRF) either Lat, Long and Height (or heaven forbid actual ECEF), anybody that really needs to know has the data and with modern software all they need to know in short order.
SPC's were not invented with easy world coordinates and geodetic software in mind. It's like using a wagon wheel instead of current tire. I can hitch up my mule team and head to the county seat or get in my current car. Either will work but I get there in my car a lot quicker and comfortable. So I take the car, don't even have the team and wagon.
> I choose to do it the other way, use an LDP (near the truth) and supply the LDP projection info for those to use out of the box and also to convert to some other larger scale projection like SPC or UTM IF they have the need.
Actually, I think you're missing the point. There is no LDP that would fit that county that would have distortions (scale errors) smaller in apparent surface distances returned than the method I use. So, my method is actually better from the standpoint of yielding distances that are more accurate than a county LDP would. I assume that no surveyor would seriously propose generating a new LDP for every tract of land unless he or she hadn't fully thought that through.
> Actually, the surface distances computed using a project CSF will be much better approximations of what a person would actually measure at ground scale than any county-wide projection could possibly accomplish. This approach is the superior one.
>
I would agree with the first part of this statement. It's about resolution really: a county-wide scale factor compared to a project-wide scale factor. Whether you accomplish this through LDP or CSF, the principle is the same, not unlike the notion of using a county-wide CSF.
Whether one approach is "superior" to another is subjective and highly dependent on the goals of the surveyor. As LR notes, he likes North to be near North and inverse coordinates to match measured distances. LDP is a good choice for him. You prefer canned projections that are more commonly supported in software ("widely supported" is debatable given that consumer grade software generally doesn't offer a State Plane option) and so State Plane makes is a good choice for you. It is kind of cute when you phrase subjective opinions as fact, though.
Well, you are obviously not using modern tools and software. The ones that keep the coordinates in 3D on a world system, that can convert to any projection with just a few key strokes. I work in 3D world coordinates and project them at will to make the most sense of any project I'm working on, usually near to ground distance and north per the earth. This is what they have been trying to do down through the ages (the PLSS where I'm at and well before SPC's were cooked up). I report the survey results on that basis (ground distance - my LDP grid at an average elevation - and a basis of bearing between real monuments very near real North). These surveys can be followed easily by other surveyors, they can be converted into SPC's or UTM or any of the giant projections. They can be compared to the original record usually not remotely related to any SPC and any landowners own measurements on the ground (without using scale factors of angle rotation).
I can convert back and forth from my working LDP to any SPC in the field with a few buttons pushed on the data collector. Any modern surveyor should be able to do this. Why should we restrict our work to some particular SPC and then be constantly rotating to match what we find on the ground and rotating to figure out directions.
So why report you surveys in some esoteric system that need some combined scale factor to figure out the real distance and some angle needed to rotate the lines to figure out which way you are going?
Congratulations!
I suppose we all have varied error budgets. I can't see squandering mine on a systematic error induced by ignoring the combined factor. Kent's example 0.999861 would translate to 0.14' per thousand. I measure better than that. I surely wouldn't want my actual observational errors added to that.
Congratulations!
I worked on some large control projects back in the day with distance meters and T2's. I learned a lot about distances and one of the things that always stuck with me is that when shooting a distance you need to do them both directions and in some cases they will be different to the same points depending on which direction they are shot, at least the horizontals will.
One I clearly remember was .4' different, and if you work the math it made sense. Those where the days of NAD27 and reducing each distance to state plane by hand using a set of tables for the grid value and the elevation for the sea level value.
Exactly. And the difference between using a 3 in the seventh place instead of a 1 is 0.2 parts per million, or 1 part in 5 million. I've never known the exact value of a whit of difference, but I'll bet that 1 part in 5 million qualifies as less than one.
Anyway, an average combined factor should include a judgment component.
> Actually, I think you're missing the point. There is no LDP that would fit that county that would have distortions (scale errors) smaller in apparent surface distances returned than the method I use.
LDP does not stand for "No Distortion Projection". Using an LDP zone does not preclude providing a CSF for further refinement. Even with and LDP Zone the size of several counties you would still achieve significant improvement in scale factors and convergence angles, 900 feet of vertical relief notwithstanding.
I first suggested the idea lightheardedly. I figured a fellow like you would relish the experiment. Your intransigence surprises me.
Congratulations!
Been talking to some friends about that via email. If you think about it, even disregarding the variations in the geoid, vertical (the direction that an optical plumb points) is not parallel on Station A with vertical at station B. They converge toward the center of the Earth and diverge with elevation. So, as you say, a horizontal distance from A to B, will not necessarily be the same as from B to A, particularly if there is a lot of elevation change between them. It has me thinking that using a projection of some sort may always be a good idea for reducing measurements, even if those measurements aren't really related to an accurate geodetic position or direction.
> I first suggested the idea lightheardedly. I figured a fellow like you would relish the experiment. Your intransigence surprises me.
hmmm
Also, how different software handles projections can leave you with a mess. See the prior thread on Carlson spitting out "incorrect" Geodetic coordinates based on a scale factor being entered. Most of the time, I am better off working on an LDP and entering the projection in the GPS software (which is more used to dealing with projections, but still can vary widely) Be careful out there!
Congratulations!
I've done the individual corrections quite a few times when running a traverse with fairly long EDM shots where height changes on a given shot might be as much as 1500 - 2000 feet. Generally what we would do is use a mean height factor and mean correction for location within the zone. Can't say that I've ever bothered to compute a ground to grid both ways - it just seemed intuitive to use the middle of the line for correction purposes. But I can certainly believe differences of 0.4' (or more) with a 4 mile shot and height difference of 2000'. I might have to go dig up some old notes and try this.
I see no problem with multiple projections in a county or single use LDP's. In fact, they provide advantages over your methods. The scale factor being nearly 1, allowing both conventional and GPS to produce and report ground distances being the main advantage.
So the difference between the highest and lowest CSF, applied over 0.6 mile is ....
0.04 ft 😛
The difference between using a CSF and not is quite significant, but where in the midst of that range you pick one is a nit-pick.
> Also, how different software handles projections can leave you with a mess..
StarNet handles custom projections readily. Kent has all the software he needs to do the job.
"I'm thinking Port, right?"
Whatever's cheapest, really, and pairs well with living in the past 🙂
Don
> So the difference between the highest and lowest CSF, applied over 0.6 mile is ....
>
> 0.04 ft
>
> The difference between using a CSF and not is quite significant, but where in the midst of that range you pick one is a nit-pick.
I don't think I'd agree with that entirely. I'm seeing discrepancies of only 0.02 ft. between recent measurements between the same corners nominally half a mile apart. So the 0.04 ft. that is thought to be the threshold of measurability ( 🙂 ) actually isn't in practice.
StarNet handles projections in the field? My mistake, I thought it was office software.