Re: Conversions

> do nay of you know know to convert Northing and Eastings to Latitude and
> Longitude. I manage a large (35 Ac.) soccer complex and the fields are
> laid out in Northing and Eastings. We have a Trimble DGPS unit and I
> would like to convert to Lat. and Long. However the 3 control points as
> well as the corners of all the fields are Northings and Eastings. Any help
> would be greatly appreciated.
>

As someone already said, the North and East coordinates would have to be
projected from latitude and longitude for them to have a conversion back to
latitude and longitude...and UTM or State Plane are projected from latitude
and longitude.

However, you want to use the GPS to work with the existing local North and
East system ? You have a differential GPS system so that the result will be
accurately valid ? Okay, set up on two control points and take latitude and
longitude readings. Convert the latitude and longitudes to UTM coordinates
and inverse UTM grid direction and distance based on the UTM coordinates.
Now calculate local grid direction and distance between the same two points
using the local North and East coordinates. Now apply a directional rotation
to all of the local coordinates so that they have the directional
orientation of UTM. Now note the difference between the UTM North coordinate
of a control point with the local rotated North coordinate of the control
point and do the same with the East coordinates of the same control point.
Now apply these differences (as translation) to each local rotated North
coordinate and to each local rotated East coordinate. And you're done. Each
local North coordinate has been rotated and translated and each local East
coordinate has been rotated and translated. Now when a latitiude and
longitude reading is taken it can be converted to UTM North and East
coordinates and be spotted relative to the rotated and translated local
coordinates (which are now approximately UTM)...or a rotated and translated
local coordinate can be converted to latitude and longitude with UTM
conversion and reached with the GPS.

Formulas:

E1 is the East coordinate of Point1, E2 is the East coordinate of Point2, N1
is the North coordinate of Point1, and N2 is the North coordinate of Point2.

Grid direction of Point1 to Point2 is InvTan((E2 - E1) / (N2 - N1)) . If
(E2 - E1) is positive that is East or if negative that is West. If (N2 - N1)
is positive that is North or if negative that is South. And this spots
direction calculation in a four quadrant system which can then be converted
to a navigation bearing.

Grid distance is the Square Root of ((E2 - E1)^2 + (N2 - N1)^2) .

North coordiante grid forward is Cos(Direction) * distance plus the starting
North coordinate where Direction is a navigation bearing as an angle
clockwise from North.

East coordiante grid forward is Sin(Direction)* distance plus the starting
East coordinate where the Direction is a navigation bearing as an angle
clockwise from North.

North coordinate rotation from a N,E of 0,0 is Cos(RotatedDirection) *
Distance...where the distance is calculated between the N,E of 0,0 and the
point to be rotated and where the RotatedDirection is the calulated
direction from 0,0 to the point with rotation angle netted to it...

Then the East coordinate rotation is Sin(RotatedDirection) * Distance...


And here is a user link to 'Geodetic/UTM-Grid Utility' :

http://www.kbhscape.com/gps.htm


.

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