Quick Tips for Using COLUMBUS

Local NEU (north, east, up) Coords

Sometimes you need to transform a local North, East, Up (NEUp) coordinate system to a geodetic coordinate system, or do the reverse (in other words, geodetic to local NEUp).

• This task can be performed with practically no distortion if all points to be transformed were laid out from a single point such as in a radial survey (Example One below).

• Alternatively, if your local N, E, Up survey was laid out by repeatedly moving the instrument as you laid out new points, some distortion in the projection will occur. It will be rather insignificant for projects spanning a small area (less than a kilometer square), but will increase as the size of the project grows (Example Two below.)

Example One:

Suppose you set up at Station 'A' and then measure out dozens of new stations by turning angles, zenith distances and slope distances to each station. Your total station software then calculates a local N, E, and Up coordinate for each of these radial shots (with no corrections for curvature or convergency in the calculations.) Later, you decide to transform each of these stations from local N, E, Up to geodetic coordinates (latitude, longitude and hgt). All you need is the local N, E, Up coordinate of station 'A', the latitude, longitude and height of station 'A', and the remaining local N, E, Up coordinates to complete the transformation. Since the stations were originally laid out from Station 'A' (and only this station), the transformation can be calculated exactly.

Example Two:

Suppose you set up at Station 'A' then lay out Stations 'B' and 'C'. You then move the instrument to each of these new stations and lay out additional stations. As you create the network, you move to the newly established stations in order to lay out additional stations. In this scenario, you can still transform your local N, E, Up coordinates to geodetic with only a small amount of distortion (the amount depends on the size of the project). To minimize distortion, you should select a station of transformation which is near the middle of the project (for example, station 'M'). For that station, you need to know its local N, E, Up coordinate and its latitude, longitude, and height coordinate (just like in Example One).

The transformation computation procedure in COLUMBUS is the same for Example One and Example Two. It is described below by manually entering the station coordinate data through the data management grids (to simplify the explanation).

To calculate Local N, E, Up coordinates from/to geodetic coordinates, do the following:

1. Run COLUMBUS.

2. From the File menu, select New.

3. From the Options menu, select Datums and select the datum to be active.

4. Click OK.

5. From the Data menu, select Stations.

6. For Geodetic to Local N, E, Up:
   1. Select the Geodetic grid, and enter the geodetic coordinates for each station. Be sure to include the station of origin (the station from which to perform the transformation).

   2. Select the Local NEU grid, and enter the Local NEU coordinates for the station of origin.

   3. Click Keep and Exit.

   4. From the View menu, select 3D Geodetic.

7. For Local N, E, Up to Geodetic:
   1. Select the Local NEU grid, and enter the Local coordinates for each station. Be sure to include the station of origin (the station from which to perform the transformation).

   2. Select the Geodetic grid, and enter the geodetic coordinates for the station of origin.

   3. Click Keep and Exit.

   4. From the View menu, select Local NEU.

8. From the Tools menu, select Transformation | Local NEU <--> Geodetic.

9. Click the Mean Geo button to bring up a list of geodetic stations to select as a station of origin. For Example One above, you would select Station 'A'. For Example Two above, you would probably select a station near the middle of the project (for example, station 'M').

10. Click the Mean NEU button to bring up a list of local NEU stations to select as a station of origin. For Example One above, you would select Station 'A'. For Example Two above, you would select station 'M'.

11. Click the Compute button, and select the station(s) you wish to transform by clicking on the station name(s).

To keep the newly-computed coordinates into memory so they can be saved to a COLUMBUS input file, exported or used in another area of COLUMBUS, click the Keep button.

Hint: Before exiting COLUMBUS, save the station data to a COLUMBUS data file for future use.