Real-World Applications of COLUMBUS
Calculating Loop Closures and Traverses
1D, 2D, and 3D (vertical, geodetic, State Plane, UTM, custom projection, and local plane) loop closures and traverses can be calculated from several different observation types. You are no longer required to group your observations into sets in order to run a traverse. Furthermore, you can now include redundant observations (between station pairs) as part of the forward computations.
You wish to compute a 3D Geodetic Traverse starting at station A and continuing through station B, C, D, then back to station A (as in a loop.) You have GPS vectors between all station pairs. Between station C and D, you also have a Zenith Angle and Slope Distance.
Here is what you do.
- Change the view to 3D Geodetic (if not already set.)
- Define the route by first right clicking on station A followed by station B, C, D, then A again.
- Invoke the Tools | Cogo | 3D Geodetic Traverse command or the handy Tool Bar Button (with tip entitled Compute 1D, 2D, or 3D Traverse.)
Note: If the traverse has a valid starting horizontal angle ( * ) or starting direction set pointing into (or back at) the first station, you will be prompted with a dialog asking you if the first station selected should be treated as a backsight only. The dialog explains the rest.
* Assume a traverse, defined by you, starts at station A, then to B, then to C, then to D.
A valid starting horizontal angle is one that either backsights or foresights station A. The other end of the angle must point to station C. The angle is measured from station B.
A valid starting direction set (or partial set) is one that is measured at station B and points to station A. There must also be a second direction that is measured at station B and points to station C. Furthermore, both directions must belong to the same direction set number.
- You will be presented with a list of all applicable observations for the entire traverse. Select/Deselect any observations you want/don't want used in the traverse computation. Click Ok to begin the traverse computation.
Since station C and D have redundant observations between them (in other words there are more observations provided than are required to compute the forward position), a weighted average of these five (dx, dy, dz, zenith, slope dist) observations will be used for this leg of the traverse. The weight applied is identical to that used in a 3D Network Adjustment. The estimated errors of these observations (GPS covariance matrix and Zenith/Slope standard deviations) will be used to weight this leg.
The initial station A and final station A are the same in this simple loop. For the purposes of using unique names, the second reference to station A (i.e., the closing of the loop) will result in a station called A (001). This is only a temporary work station which will be destroyed when exiting the results dialog.
- The traverse results are then displayed in the results dialog. For this example, station A (001) will appear last, since it is the last station in the traverse.
- To keep the newly computed positions, invoke the Keep button. The station names will appear in a list ordered by the route of the traverse. If you choose to keep the coordinates for station A (001), they will actually be kept into station A as expected.
Modify an existing traverse route (or defining the route without a mouse):
When setting the route for traversing, designing (pre-analysis) of a network, or area calculations, the route is typically set up by successive point-and-click (right mouse button) operations on the applicable stations. COLUMBUS then shows a line between adjacent (selected) stations to provide a visual of the selected route.
Another way to do this (if you don't have a mouse) is to use the View | Setup COGO/Design Route dialog and select each station.
Note: Keep reading below to see how this dialog allows you to edit an existing route (created via your mouse.)
The left side list contains all the station names applicable to the current view context (1D Vertical, 2D Geodetic, 3D Geodetic, etc.)
The right side list will be empty if no route has been set up yet. If you created a route using your mouse, this list will show each station in the order you established.
To add a new station to the list do the following:
- Highlight the station in the right list (if any exist) for which you want the new station to be next to.
- Highlight the station in the left list that you wish to add. Invoke either the Insert Before or Insert After button to add the new station either before or after the station highlighted in the right list.
To remove a station from the right list do the following:
- Highlight the station to remove in the right list.
- Invoke the Remove button.
Using the steps above, you can modify an existing route or create a completely new route from within this dialog. When you close the dialog, the view will be updated to reflect your route changes.
1D and 2D Traverses
Loop closures and Traverses can also be calculated for 1D vertical and 2D networks following the same logic described above:
- From the View menu, simply change the view to either 1D Vertical, 2D Geodetic, 2D State Plane, 2D UTM, or 2D Local NE.
- For 1D Vertical networks, only the Height Difference and Local Up observations apply.
- For 2D networks, GPS observations do not apply.
Astro Geodetic terrestrial observations
If your baselines are made up of Astro Geodetic terrestrial observations (for example, Az/Zen/Chord set leveled in the direction or gravity, which is very common), you may be able to improve your results by allowing COLUMBUS to convert these into Geodetic terrestrial observations during the computations.
To do this, you need to provide the deflections of the vertical for each station connected by Astro Geodetic terrestrial observations by doing the following:
- From the Data menu, select Stations and select the Geodetic grid.
- Enter the deflection of the vertical values for each geodetic station.
- When done, click Keep and Exit to update the record for that station.
- Continue from Step 3 above.
If you prefer to use the same deflection of the vertical (for each station), enter the Options - Global Settings dialog and set the approximate Deflections (E-W and N-S). This eliminates the need to set deflection values at each station.
Network Adjustment and Coordinate Transformation
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