convert Ground System coordinates to Google Maps and GPS

What are you using to convert?

In Excel:
Get a Northing and Easting on two points and rotate / translate to SPCS. You can use excel to calc it.
If you can run from SPCS to Lat/Long then go from that.

Do you need the COGO excel formulas?

If you are given
N 305160.43
E 2206939.84

that looks like either State Plane or modified state plane. Unfortunately there is a common practice of scaling SPC coordinates to get modified coordinates at the average ground elevation for a project, which is fine, but then not doing anything to make them look different than the SPC, which is bad. The best practice would be to subtract off the millions of feet from the coordinates, which signals that they are different but is easy to reverse.

Confusing modified coordinates for true SPC will give you errors that are large enough to be important but not large enough to be totally obvious.

You need the "metadata" or description of how the coordinates were defined, to go with the numbers. In particular, there will be a number like 1.000xxx or 0.999xxx to multiply or divide by to go between coordinate systems. There should also be information like US Survey feet versus International feet (I didn't look up which is usually used in Kansas), and which datum such as NAD83(xx).

I used a free tool from the Corps of Engineers, called CORPSCON and find that those values, if interpreted as Kansas North (zone 1501) true state plane values in US Survey feet, gives
N 39 07' 42.3" W094 50' 44.9"
but if there is a scale factor for conversion, then you will have to get it from whoever gave you the coordinates and apply that before converting to latitude and longitude.

All this may end up being more complicated than using the other suggestion of fitting to two known points on site.

The other problem is your expectation of accuracy. Neither Google nor a recreational-grade GPS will reliably give you 2-ft accuracy. Maybe more like 10 ft on a good day with outliers well beyond that.

Try this... Earthpoint.

As said elevation will be your big problem.

If the point in yellow you posted is in the correct location on the image you can assume the ground is state plane for approximate mapping purposes. If not, some calculations are needed as Bill93 describes.
This was done using "Fly to" http://www.earthpoint.us/StatePlane.aspx
Calculated Values - based on Degrees Lat Long to seven decimal places.
Position Type State Plane - Kansas North
Degrees Lat Long 39.1284231°, -094.8457940°
Degrees Minutes 39°07.70539', -094°50.74764'
Degrees Minutes Seconds 39°07'42.3233", -094°50'44.8584"
State Plane X Y (Meters) 1501 672676.609mE 93013.084mN
X Y (US Survey Feet) 1501 2206939.840ftUSE 305160.425ftUSN
X Y (International Feet) 1501 2206944.254ftE 305161.036ftN
UTM 15S 340453mE 4332650mN
MGRS 15SUD4045332650
Grid North -1.2°
GARS 171LU35
Maidenhead EM29ND80MT17
GEOREF FJLK09250770

Since no one else has said it, I will. You cant do what you are describing without knowing State Plane Coords, datums, conversions, scale/elevation factors. Hire a surveyor. You could be hundreds of feet wrong using any of the methods described here.

Thanks for your info,

The yellow dot should be on the other side (West side) of the tree line, about 60 to 70 feet west of where it is at.

OK thanks,

I was hoping this would have a more simple solution, but I guess not.

Thank You to each of you that took the time to reply,

I have contacted the engineers that drew up the plans and they are do the converting for me. I was hoping I could do it myself....

That would be approximately consistent with the coordinates being modified SPC, scaled to some project elevation, although I'd have guessed it to be much more than 60 or 70 ft.

You need the exact definition of their system, with NAD datum, which foot, and the number that isn't quite 1.00000, to actually calculate back to the true SPC values before converting to lat-lon.

From an NGS data sheet in the area I get a CSF of 0.99991808.
Assuming the scale was from 0,0.
and the leaves must be off....but still
305160.43 x 0.99991808= 305135.43
2206939.84 x 0.99991808= 2206759.05
It will be interesting to see what they give for SPC.

25' S and 180' W of the ground pt

> Thank You to each of you that took the time to reply,
>
> I have contacted the engineers that drew up the plans and they are do the converting for me. I was hoping I could do it myself....

awesome! Please come back and let us know how it all works out! good luck.