State Plane Coords to Ground Coords

Autocad

> Does anyone know of a Program that I can use to convert GPS collected State Plane Coords into Ground coords? Perhaps someone has written one?

Excel will do that. Unless you have StarNet, which has a function to do that. And various forms of CAD can be used to do it, but that would be my third choice.

There is no such thing as "ground coordinates"! SPC is SPC - period! There are grid to ground conversions for distances between stations, but you should NEVER mess with the coordinates. Or if you do, they are not SPC's! They are just an arbitrary coordinate system.

I am new at this. I understand that state plane coordinates are on a flat plane that is not at ground level. My ranger 3 field controller with survey pro will calculate mapping plane ground coordinates based on an opus point or GNSS point with good spc coordinates that has an ellipsoid height and an acceptable reference geoid. It will calculate the ground coordinates based on this one point or several if you collect information on several known points.

Your answer is "it depends" on what you really need. Grid is grid, and it is best not to mess with it, but the downside is that your ground distances will be off by the grid to ground scale factor. For engineering work, you need ground distances. It may be best to establish a site ground coordinate system and use that.

That's my two cents worth. :-/

There's no such thing as SPC! Only WGS84(2011)! If you apply a transformation you'll just wind up with some arbitrary coordinate system! 😛

I completely agree that leaving things on vanilla SPC is the most convenient when possible, but I can think of a plethora of reasons one would want to utilize a local LDP, or use a centroid, or a site calibration.

Most data processing software can be used to scale SPC coordinates to make the distances on inverse nearly match ground. It is rather simple to compute a combined factor for an area and apply it in Excel as well. This method is just fine for small areas. The distortions introduced won't be significant if done correctly and constrained in area. The maximum area is determined by position within the projection and vertical relief.
Good luck, Tom

:good:

> There's no such thing as SPC! Only WGS84(2011)! If you apply a transformation you'll just wind up with some arbitrary coordinate system! 😛
>
> I completely agree that leaving things on vanilla SPC is the most convenient when possible, but I can think of a plethora of reasons one would want to utilize a local LDP, or use a centroid, or a site calibration.

I figured with a name like Sat Al you were going to go meta one more time and say there's only ECEF! 🙂

COMBINED FACTOR (GRID) = 1.000002425 (example)

1 / GRID = 0.999997575

Local Project Plane Coordinate Conversion Equation:
a. Local Project Coord y = [(State Plane y - hold point y) 1/grid factor] + hold point y
b. Local Project Coord x = [(State Plane x - hold point x) 1/grid factor] + hold point x

There's no such thing as WGS 84 (2011). I think you mean NAD 83 (2011). The current realization of WGS 84 is WGS 84 (G1674).

True, true, but I didn't want to steal your thunder. The point was well made.

> I figured with a name like Sat Al you were going to go meta one more time and say there's only ECEF! 🙂

Thank you for the reply. So far you have made the most sense but still confused

COMBINED FACTOR (GRID) = 1.000002425 (example)

1 / GRID = 0.999997575

Local Project Plane Coordinate Conversion Equation:
a. Local Project Coord y = [(State Plane y - hold point y) 1/grid factor] + hold point y
b. Local Project Coord x = [(State Plane x - hold point x) 1/grid factor] + hold point x

First question is is the 1/ Grid you mention the same factor I get using corpscon?

Second is can you give me an example. Lets say my NM West Sp coords are
North 1684447.5880 East 2389863.6630 Elev 6904.82 shot by trimble R-8?

Or do you have the formula I could enter into excell.

I realize you have better things to do and as ashamed as I am I will admit I have been Surveying for 37 years and have never really had to do this, I used to do it once in a while but for the last 20 years haven't had to. Now I'm working on a Large project covering 4 Townships on the Navajo Res. and need to get a good grasp of it.

If not, no worries. Maybe if I stare at what you wrote before a light bulb will go off.

Getting Old Sucks 🙂

Jim

Multiply the state coordinate system coordinate by the combined scale factor and you have the ground coordinate.

Pick one factor for your project area

Thanks my friend.... I thought I remembered it wasn't that tough if you had those two items but as I said, getting Old Sucks:-D

Hey, I understand the getting older thing 😉

The formula I gave you is just ONE way to calculate "ground" coordinates, and it's how the DOT's I work with all do it.

In essance you are scaling the coordinate around 0,0 by the combined factor.

Scale in Autocad does this.

In TBC you can do it also with the local site setting, it allows you to scale up, picking the point you want to scale from, so pick grid north and east of 0 0 and type in a scale factor and you have new coordinates. I set up my jobs before even leaving the office and the advantage of doing it in TBC is that your job is seemless from start to finish and no need to worry about your system.

Make sure to keep records, TBC will print out a sheet with all the metadata, I throw it in the file for each job.

Of course EXCEL does it also.

Desparate jim

I use Liscad which has option of working in grid or plane on screen. The coordinates always stay as grid, but you can set screen and distances to plane to enable you to work in plane and added plane data which converts generated coordinates to grid coordinates.

If you are working with a small area and using Total station then rather than changing scale factor on TS and perhaps one day forgetting, Liscad allows you to enter a scale factor and it will then output coordinates as local plane coordinates so that set out and or further point location will be plane data ( These generated coordinates kilometres from the grid coordinates and unable to be accidentally added back to the job). When the additional survey plane data is uploaded into grid coordinate job the grid coordinates are computed.

RADU

If you have control points in state plane, converting to ground is something everyone will do differently. You can scale from the origin, an assigned control point, or an assumed centroid point. You can give 10 surveyors 10 state plane control points and you can end up with 10 different ground datums. You are scaling the points by a factor. from where you scale, unless not pre-determined, is up to you.

I'll second that one. While there certainly are very bad things you can do with SPC, those who claim there is only one correct way to do most things are mistaken.
Choose the method that meets the needs of the project. Document what you did so it doesn't morph Into something you never intended it to be. Last but not least, learn before you leap. We are all bound by the Code that demands we not accept assignments beyond our ability...

Please, Please, Please be very careful about this!

ALWAYS lop off an integer amount to absolutely avoid
having someone accidentally ASS-U-ME they are valid SPCS
(just because they "look" like them)
ex
N 2,123,456.789 E 6,123,445.789 SPCS

N 123,456.789 E 123,445.789 "Ground"

NEVER use the SPCS origin as the base for scaling.
Result coordinates will be way off intuitively wise.
I can't think of any reason for doing this.

TYPICALLY pick a point at the approximate center of your job area.
OR a Control Point near it.
Use this as your scaling "epicenter".

Using your Integer Cutoff Amounts you will have a easy check.

If you use SPCS Control Points throughout job and Ground (scaled) distance,
You'll never be too far off as far as absolute position.

And if you are raying out a hardscape feature (ex. ends of a pipe)you will be off nil.
it's the difference in the two positions not the difference in distance from control.

May need to rethink if you are at 10,000 ft elevation

In my area it's Lambert so always cautious about distances in N-S direction
due to varying Scale Factor (if relevant)