
Quick Tips for Using COLUMBUS
Geoid and Deflection of Vertical Modeling
Performing deflection of vertical modeling at any time within COLUMBUS
Modeling deflection of the vertical values and applying them to each of your geodetic station records allows COLUMBUS to correct your astronomic observations to geodetic observations during network adjustment and COGO traversing.
 Astronomic observations are those measured in the field where the instrument is leveled in the direction of gravity.
 Geodetic observations are "leveled" in the direction of the ellipsoidal normal and are the assumed observation type for all geodetic computations.
When deflection of the vertical values are not known (or are set to 0.0 within the geodetic station record), the direction of gravity and the ellipsoidal normal are assumed to be aligned in the same direction, and therefore no correction is applied. The vertical angle astronomic observation usually receives the largest modification when deflection of the vertical corrections are made.
Note: While deflection of the vertical corrections can be applied to any survey containing astronomic observations, they are usually only used in high precision surveys. For more information, see RealWorld Applications of COLUMBUS: Mixing GPS and Terrestrial Measurements in a Network.
You can perform deflection of the vertical modeling at any geodetic station at any time during your session with COLUMBUS. Each station you wish to model must have known geodetic coordinates (latitude and longitude). These coordinates can be obtained from network adjustment, coordinate transformation, geodetic traversing, and so on, all within COLUMBUS. Or you can simply enter the geodetic coordinates for a station and model it immediately (described below). Whichever way you chose, the modeling steps are essentially the same.
COLUMBUS supports Deflec 90, Deflect 93, Deflec 96 and Deflec 99 modeling grids. To calculate deflection of the vertical values from geodetic stations using Deflec 99, do the following:
 Run COLUMBUS.
 From the File menu, select New.
 From the Options menu, select Datums and select the datum to be active (usually WGS 84 or NAD 83).
 From the Options menu, select Directories and enter/select the DEFLEC99 modeling files for your area. These files have a *.bin extension. You only need to select one of the two file pairs (for example, e1999u08.bin or x1999u08.bin). COLUMBUS will automatically look for the other file pair in the same folder.
 Click OK.
 From the Data menu, select Stations. Select the Geodetic grid and enter the known geodetic coordinates (lat and long) for each station you wish to model.
 Click Keep and Close.
 From the Tools menu, select Deflection Modeling. Click the Deflec 99 (*.bin) radio button.
 Click the Stations button to bring up a list of stations to model. Select the stations to model them.
 Click the Keep button to keep the newlycomputed station data (new deflection of the vertical values) into memory for each geodetic station modeled. They can then be saved to a COLUMBUS input file, exported or used in another area of COLUMBUS.
Hint: Before exiting COLUMBUS, save the station data to a COLUMBUS data file for future use.
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Performing geoid modeling at any time within COLUMBUS
You can perform geoidal modeling (determining geoidal heights) of any geodetic station at any time during your session with COLUMBUS. Each station you wish to model must have known geodetic coordinates (latitude and longitude). These coordinates can be obtained from network adjustment, coordinate transformation, geodetic traversing, and so on, all within COLUMBUS. Or you can simply enter the geodetic coordinates for a station and model it immediately (this case is described below). Whichever way you chose, the modeling steps are essentially the same.
COLUMBUS supports geoid 90, geoid 93, geoid 96, geoid 99, geoid 03, Canadian HT2_0, and EGM 96 modeling grids.
To calculate geoidal heights from geodetic stations using geoid 03, do the following:
 Run COLUMBUS.
 From the File menu, select New.
 From the Options menu, select Datums and select the datum to be active (usually WGS 84 or NAD 83).
 From the Options menu, select Height Updates  Height Update Method and enable the desired Geoidal Height Update option.
You can either float the stations current orthometric height value or the current ellipsoidal height value during the modeling. If you choose to float the orthometric height value, it means that the ellipsoidal height field will be held fixed and the orthometric height field will be calculated from the ellipsoidal height and the modeled geoidal height.
Where: ortho hgt = ellip hgt  geoidal hgt.
 From this same dialog, enter any known geoidal modeling bias for your area. This bias is a constant value you expect the model to be off from its true value. If you don't know, simply assume it is zero. See the Help topic within the dialog for more details.
 Click OK.
 From the Options menu, select Directories and enter/select the geoid 03 modeling file for your area. These files have a *.bin extension.
 Click OK.
 From the Data menu, select Stations. Select the Geodetic grid and enter the known geodetic coordinates (lat and long) for each station you wish to model.
 Click Keep and Close.
 From the Tools menu, select Geoid Modeling. Select the Geoid 03 radio button. Click on the Stations button to bring up a list of stations to model. Select the stations to model them.
 Click the Keep button to keep the newlycomputed station data (new height data) into memory so they can be saved to a COLUMBUS input file, exported or used in another area of COLUMBUS.
Hint: Before exiting COLUMBUS, save the station data to a COLUMBUS data file for future use.
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