TGO & Lambert Conformal projections to ground

I wish I could help, but maybe how we do it will help you out.

Once I start on the grid, I stay on the grid. All GPS work is done via being on the grid and connected via OPUS. TGO only keeps my grid points.

Next, with the TS, we stay on the surface. I know, I know, WTF right. We collect our data with the ranger on the surface.

Then, when I bring in my points into Carlson, and I reduce the data, I tell it to figure the scale factor (after setting the parameters in the job) to each leg and calculate it as it goes.

Finally, all of my coordinates are on the grid, my crew didn't have to screw up one more thing like fat fingering a scale factor or 0.00999 or 9.9999 and I have to invent new physics to figure out how to fix it.

Also, and admittedly I catch flak for this from some, if I work on the grid, I report on the grid. Whether it's a 900-acre gas lease or a 15-acre boundary, the distances reported are grid, always.

Now, I must admit the secrete to my success is that most of the areas that I practice in are VERY near the zone line so scale factors are very nearly surface and my average elevation for my project areas ranges between 200' and 650'.

> Next, with the TS, we stay on the surface. I know, I know, WTF right. We collect our data with the ranger on the surface.

WTF Kris!!!! How the hell are getting away with that!!!!:-O JK

> Then, when I bring in my points into Carlson, and I reduce the data, I tell it to figure the scale factor (after setting the parameters in the job) to each leg and calculate it as it goes.
>
> Finally, all of my coordinates are on the grid, my crew didn't have to screw up one more thing like fat fingering a scale factor or 0.00999 or 9.9999 and I have to invent new physics to figure out how to fix it.

This is sort of what we do now except we adjust everything the other way to ground. I was just after a way to combine the two so that I don't have to adjust. And if we work on the grid (very rare) we report in grid.

> Now, I must admit the secrete to my success is that most of the areas that I practice in are VERY near the zone line so scale factors are very nearly surface and my average elevation for my project areas ranges between 200' and 650'.

Ah, must be nice to work near the LOES. And... not have to work at 2700-7500' near mountains.:-P

Hi Rob,

I ASSUME that the only reason you want to use a Lambert Projection, is to maintain alignment (agreement) with the State Plane Grid Bearings in the state in question (I can't think of any other reason).

If that's REALLY what you want to do, then a Single Parallel Lambert would be the path of least resistance, although setting one up [PROPERLY] may NOT be immediately intuitive.

It can get [more than a little] confusing, and I don't generally recommend it. It CAN be done, and it works FINE, but a LOT depends on just what you are trying to accomplish.

I can't write a dissertation that covers all bases today, but if you want to give me a call (307-789-0291) I'd be happy to outline the basics for you (or maybe try and talk you out of it altogether, and convince you to just use a Transverse Mercator).

Loyal

Loyal,

I can't use a TM projection in Washington or Oregon. Or can I? At least not with TGO Coordinate System Manager.

Yes, I'm trying to maintain grid bearings and be able to use true ground distances and inverses between GPS and conventional equipment.

Rob,

You can use a Transverse Mercator (or a Lambert [or any other projection] for that matter) ANYWHERE on Earth, you just have to DEFINE it first. The new Oregon LDP(s) are actually a suite of different Projection "types" if I recall correctly.

Before we get too carried away with whipping up a psuedo-SPC for ya, you should check to see if Oregon has already adopted an new LDP Zone in your area of interest.

See: http://www.oregon.gov/ODOT/HWY/GEOMETRONICS/ocrs.shtml

Loyal

Loyal, you are correct, TM, LCC and OM zones are all used. Whatever type of projection that worked best for a particular area was used, thus the mixture of projection types.

Rob, if one of the Oregon LDP zones won't work, THEN UNLESS then is some reason not to, I would develop my own local TM, easier to work with IMHO.

I still just prefer leaving everyting on the grid, but that is just me.

SHG

TxDot does basically the same thing you are wanting to do with Lambert. They publish a list of "Surface Adjustment Factors" for each county based on the average scale factor and elevation of the county. The SAF is 1/combined scale factor. For my county it is 1.00012 . If you are working in a smaller area, you could calculate a more accurate factor for your job. By doing this county wide, the coordinates and control should match from one project to the next within the same county and into adjacent counties with the same SAF, usually east and west.

I don't have or use TGO but I have been able to duplicate their coordinate system in Survey Controller. I would think anything that can be done in Survey Controller could be duplicated in TGO but I could be wrong.

The way I did it in Survey controller is to calculate the lat long for state plane coordinate N 0.00, E 0.00 for the zone that I am working in. Set the job file for the proper SPC zone and enter the above lat long for the project location. Then enter the SAF (1.00012) in the scale factor. The coordinates I get can be converted back to SPC by dividing by 1.00012 . This works for the Central, North Central and North zones of Texas. The South Central and South zones calculate to a 0,0 point south of the equator and I haven't figured that problem out yet but I don't have many jobs there. I would think that Oregon and Washington are far enough north that it would not be a problem.

I wrote much of this from memory but I think I covered everything. If it doesn't work for you, let me know and I will find my notes to see what I missed. I keep a file on my data collector for the central and the north central zone and just change the SAF for the county I am working in. I don't re-enter everything for each job.

James
jasrowden(the at symbol)yahoo.com