SP to Ground

Best of luck to you Jim and hope you and/or your client/boss do not get in trouble. $$$$ comes to mind.

Read the guys below. They know what they are talking about.

The short answer is that it depends what you are doing. The long answer will require you to take extensive training in what exactly GPS will and will not do. SPC's are over rated in my little guy world. I don't give a rat's patootie where I am on the planet, just my small project, so I bring all my stuff to ground and calibrate to a local datum. Never to be confused with SPC's.

Remember that the second you hit the "GO" button to get from grid to ground, you no longer have SPC's. Think in terms of that GPS box in your truck as just another tool, just as you would your total station or Shoensdtat or shovel or hammer you will likely need (so as not to beat your head against the wall and get in serious trouble).

You can use this to do them one at a time:

Web Calc

Do you not have Excel?

Actual surveying programs are:

Trimble Business Center, Leica Geo Office, Carlson Survey...

Thanks, yes I have excell.
I also have TBC but am just getting started on it. You can email at [email protected] if you wish... Thanks again

I hear you Loud and Clear my friend. Been Surveying for 37 years and really never had to do this?
Work for the BOR and they are building 200 miles of 40" h20 line. New here and used to do things my way. Now I am the Boss of 3 guys who know how to push the GPS buttons.

$$$ isn't as big of an issue as my ethics. I'm even licenced in 4 states but never really had to do something like this. I'm locating a FX line that covers about 25 miles on the Navajo Nation. Doing this for the BIA. They gave me a legal that someone wrote of the fx? they think but have no idea about the datum. Guessing assumed Ground.
We are locating it using GPS and SP coords to compare the two. Hence my issue
If you want to email me its [email protected]

Thanks for the Support. I sure miss my T-2 and Chain 😀

Just shot you an email, I'll convert them for you.

I know quite a few boundary surveyors that do impeccable work, but have long forgotten anything about SPC, projections, etc.

200 miles is most likely too long a distance to use local plane coordinates. If you want to avoid using several scale factors along the route the solution may be LDP design.
1) what is the average bearing of the 200 miles
2) what is the approximate high and low elevation

You should be able to key in a projection to Trimble that will allow GPS coordinates to output LDP coordinates.

> 200 miles is most likely too long a distance to use local plane coordinates. If you want to avoid using several scale factors along the route the solution may be LDP design.

Isn't 200 miles a bit of a stretch to use a LDP?

LDP

> > 200 miles is most likely too long a distance to use local plane coordinates. If you want to avoid using several scale factors along the route the solution may be LDP design.
>
> Isn't 200 miles a bit of a stretch to use a LDP?

Not necessarily...

The only real limitation to the "length" of an effective LDP, is relief.

You can design and LDP for a route project in any direction (East-West = Lambert, North-South = Transverse Mercator, any other = Oblique Mercator).

Here in the Great Basin, about the only option is Transverse Mercator due to regional geography. And even then, elevation change usually eats your lunch (and distortion budget) before you get much more than a couple hundred miles (best case).

Loyal

LDP

After rereading Jim's post I'm not sure if his project is 200 or 25 miles. Same questions and answers either way.

LDP

Thank you for your comment, I got to do a bit of professional development on that topic.

For argument's sake, say I have a 100 miles x 100 miles box with a 20 miles wide mountain range running in the middle in the North-South direction. Would the LDP projection's direction be chosen to be aligned with the mountain range longitudinally or to cut across the mountains in E-W axis?

LDP

> Thank you for your comment, I got to do a bit of professional development on that topic.
>
> For argument's sake, say I have a 100 miles x 100 miles box with a 20 miles wide mountain range running in the middle in the North-South direction. Would the LDP projection's direction be chosen to be aligned with the mountain range longitudinally or to cut across the mountains in E-W axis?

Short version (I have a crew in the field today).

A project that size (as described) would NOT be a good candidate for a single LDP.

I would (probably) set up three (3) Zones (North-South Transverse Mercator), one each side of the Mountains, and one up the center of the mountains. The "Mountain Zone" would have a somewhat "higher" developed surface, and the "Valley Zones" on each side thereof, may have dissimilar developed heights as well (it depends).

I'm working on a project (as we speak), that has over 3000 ft. of relief, and a single Section (there are about 6 sections involved) has over 2000 ft. of relief.

Loyal

Large area projects are far beyond my expertise, but the idea occurs: has anyone done a project like this in XYZ coordinates? There would be no distortion to worry about.

Those should be available from the GPS, and are possibly what the software used to get SPC.

XYZ

Bill,

I like your thinking. And with all the computing horsepower we have today, why do we even need to screw around with projections that hardly anyone seems to understand.

Dave

Delta xyz relative to the equatorial plane is the essence of gps data. Not so long ago this was very transparent in many software packages. When I pull in older data it is never LLH or NEZ. I grab the delta xyz and apply it within my new network. The results are phenomenal. No worries about minor variations in realizations or epochs...

LDP

Thank you for your explanation. It is a good example why the UTM grid remains so popular. For people like me who do have a in-depth understanding of geodesy, "sticking with what you know" seems to be a preferred route. The UTM is simple and universal.

Learning to use LDP is on my to do list, I can see benefits. However, I am curious at the fact that proponents mention that measurements between total station and GNSS are comparable. It seems, if I recall correctly in the case studies that I read, that it does not take too far of a distance before a couple of inches of difference start to creep in between satellite-based and optical measurements. To me, the benefit of the LDP is matching GNSS and TPS observations. I am thinking that it may require a fairly small work site (depending of relief as I understand) for a LPD to be very useful if after a couple of miles, scale factor kicks in?

James

In a "typical" 1ppm LDP (Transverse Mercator) that I would use in the Great Basin, the "Grid to Design Height" (projection induced scale/distortion) would never be greater than 1.000 001 or less than 0.999 999 across the "zone limits," which would be ~8 miles either side of the Central Meridian of the Zone. There would be no [practical] limits North and/or South from the origin.

HOWEVER!!!

As the topographic conditions change within the Zone, the Grid to "ground" scale will CHANGE by about 1ppm (0.000 001) for every ~21 feet of ellipsoid height change relative to the LDP design height.

So:

If the LDP design Surface is set to [say] 6000 NAVD88 (5950 Ellipsoid Height based on a -15m 'N' value using GEOID12a), then you end up with something like this:

NAVD Grid-Ground      Scale
5500  0.999 976  +/- 0.000 001
5600  0.999 981  +/- 0.000 001
5700  0.999 986  +/- 0.000 001
5800  0.999 990  +/- 0.000 001
5900  0.999 995  +/- 0.000 001
6000  1.000 000  +/- 0.000 001
6100  1.000 005  +/- 0.000 001
6200  1.000 010  +/- 0.000 001
6300  1.000 014  +/- 0.000 001
6400  1.000 019  +/- 0.000 001
6500  1.000 024  +/- 0.000 001

So basically that LDP would give you a "sandbox" to play in, that is ~16 miles East-West, and WHATEVER North-South, limited to a thousand vertical feet of relief, wherein your "grid to ground" distortion would NEVER exceed 25ppm (0.13' per mile), and your "Grid-Geodetic" (gamma/mapping angle) would never exceed ~6 arc-minutes.

If your project "only" has 500 feet of relative relief, then the maximum distortion drops to about 12-13ppm.

Far from "perfect," but for many projects, it works pretty well.

Loyal

James

Thank you for the numbers, it helps visualize. I don't get it yet, but I am starting to see the light.

The scale factor is the inverse of the elevation factor. Does it mean that the combined scale factor for a LDP is calculated by multiplying the scale factor by the elevation factor? If you have an example of 3 points showing the three factors (scale, elevation and combined), that would help me understand I think.

I am not in a big rush to understand, but it will be a good feeling when I do.

- - - - -

I think that the mining industry could benefit from the use of LDP projection in many sites.

XYZ is a perspective just like LLH. You still have to be concerned with realizations and epochs. You don't have to worry about Geoids or ellipsoid though.

The main driving force behind projections is in 2D mapping. XYZ does not lend itself to this very well except at the North pole and South pole. It's not easy to relate a terrestrial survey to XYZ nor is it easy to relate XYZ to a 2D "level" plane.

>It's not easy to relate a terrestrial survey to XYZ nor is it easy to relate XYZ to a 2D "level" plane.

Indeed. But software could be written with the philosophy that the XYZ coordinates are the values to be stored, and any sort of projection you want could be derived from that at any time. You would need to give it the ellipsoid, geoid, datum, and epoch, and then it could do the translation.

Every terrestrial measurement or local detail map could be translated using what would essentially be a LDP centered on that measurement or map. Instead of the total station measuring slope distance and vertical angle, converting to horizontal and vertical offsets, and considering those to be the measurement data, it would store the mark-to-mark (slope) distance and use the local projection to get a 3-D vector for direction.

That may be what Prof. Burkholder was describing. I wasn't sure because his writeup got into the technical details before establishing a picture of how it would appear to the user.