Preferences

The Preferences page is where you define various settings for computations for the current project. Changes in Preferences are saved with the current project when you click the Save Changes button. You must select a project to be active before you can access the Preferences page.

Datum / Units tab

Use to select the datum you wish to be active, or define a new datum by selecting the User Defined Datum and supplying the Semi-Major and Flattening parameters.You can also define the Linear and Angular units for Data Input and Reports. Latitude and Longitudes must always be entered in DD.MMSSsssss (Degrees, Minutes, Seconds).

Grid Projection tab

Use to select any of the predefined grid zones or set up a user-defined zone by selecting one of the first four zones, then providing the grid parameters.The first four zones in the list are:

  • User-Defined Lambert Single Parallel
  • User-Defined Lambert Double Parallel
  • User-Defined Transverse Mercator
  • User-Defined Azimuth Equidistant
  • User-Defined Steriographic Double

To create a UTM or 3TM zone, select the User-Defined Transverse Mercator zone and enter the applicable parameters in the Transverse Mercator column.

ALTA tab

Use to modify the default American Land Title Association (ALTA) settings used in many states. To return to the default settings, click the Set Defaults button. ALTA statistics can be computed during a 2D or 3D network adjustment.

Outlier tab

Use to specify the threshold at which an observation standardized residual is tagged as a possible outlier.
The standardized residual is:
  • A unitless quantity that can be compared against a unitless threshold.
  • Calculated by dividing the adjusted observation residual by the adjusted observation residual standard deviation.
  • If this value (“absolute value”) is greater than the threshold, the observation will be reported as a possible outlier. You may then further inspect the observation to determine if it should be removed from the network adjustment.

If the Standardized Residual threshold value is set to zero, Columbus will calculate a threshold value based on the Tau statistic. The Tau statistic thresholdis a function of the number of observations, the degrees of freedom and the confidence level set up for the network.

Overrides

Standard Deviations tab
Use to set a default standard deviation (SD)for any supported observation type.Any positive non-zero value will replace all observation-specific standard deviations during adjustment and traversing. For example, you have three azimuth measurements in your network:

  • Azimuth one SD set to 3.0 seconds
  • Azimuth two SD set to 10.0 seconds
  • Azimuth three SD set to 8.5 seconds

If you enter a non-zero value (for example, 2.0 seconds) in the Azimuth edit box, during adjustment each of these three individual azimuth SDs will be replaced with an SD of 2.0 seconds. Set the Azimuth edit box back to zero to use the observation-specific SDs during adjustment (3.0, 10.0 and 8.5, respectively).

Centering / PPM tab

Use to set the default centering standard deviations and PPM values for supported observation sets. Values defined here will override individual observation set values during adjustment and traversing. Set the centering standard deviations and PPM values back to zero to use the observation set-specific values.

Distance Scalers tab

Use to set a scaler to be applied to applicable observations during adjustment and traversing. Set the values back to 1.0 to apply no scaler.

Standard Deviation Scalers tab

Use to set a scaler to be applied to applicable observation standard deviations (SD)during adjustment and traversing.For example, if you have three azimuth measurements in your network:

  • Azimuth one SD set to 1.0 seconds
  • Azimuth two SD set to 2.0 seconds
  • Azimuth three SD set to 3.0 seconds

If you enter a scaler of 1.5 in the Azimuth edit box, during adjustment each of these three individual azimuth SDs will be replaced with a SD of 1.5, 3.0 and 4.5 seconds, respectively. Set the Azimuth edit box back to 1.0 to use the original observation SDs during adjustment (1.0, 2.0 and 3.0, respectively).

Others tab

Use to override the current Zenith Angle refraction coefficient for all Zenith angles and Deflection of The Verticalvalues for all stations.Deflection of Vertical settings allow Columbus to correct astro geodetic (field) observations leveled in the direction of gravity to geodetic observations leveled in the direction of the ellipsoidal normal. This correction is often applied to high-accuracy networks. To set the Deflection of the Verticalto zero for all stations, enter a small non-zero value, such as 0.00001 seconds for N-S and E-W.The Zenith Angle coefficient is used to apply a zenith angle refraction correction. The correction is computed as follows:

ZA corrected = ZA measured + (K * D) / (2 x R)K = Zenith angle coefficient (range 0 to 0.5)D = Slope (chord) distance between the AT and TO station

R = Radius of earth + Ellipsoidal Height at the AT station.

Note: To turn all settings off in this tab, set each field to Zero.

Advanced tab

Use to apply additional options and settings to both network adjustment and traversing.Traversing uses the same adjustment engine as is used for network adjustments. The difference is that when traversing, no stations along a traverse are adjusted; they are simply computed using the known observations and their standard deviations, to weight the observations. This allows you to include more than the minimum-required observations between each station in a traverse.

  • Max Iteration: The maximum number of iterations to be performed during the non-linear adjustment process. Ten is usually an adequate maximum for most projects. There is no penalty for making this number larger; it will just take longer for a diverging network to abort. Most well-defined networks converge within one to four iterations.Convergence:The convergence level that signals the adjustment is done. When the change in coordinates from the previous and current iteration differ by less than this value, the solution is said to have converged. The convergence value should be entered in the active linear units.Confidence: The confidence level upon which the statistics are based. The closer to 1.0, the greater the confidence intervals (or regions, for 2D and 3D) must become. The most common setting is 0.95 (95% confidence). Standard deviations are based on a 68.3% confidence level (0.683).

  • APriori Variance: Use this keyword to scale all observation variances (SD squared) prior to computing the weights during network adjustment. Changing this value will not change the adjusted coordinates, because this value is applied to all observation variances equally. It will change the adjustment statistics if the check box Ignore Apost Var is checked.

  • Approx Lat and Approx Lon: The approximate latitude is used in 1D trigonometric and 2D/3D Local North, East, Hgt (NEE) networks. It is used to correct for curvature and rotate average bearings to true azimuths.

    For these corrections, enter a latitude within a few minutes of the true value. The approximate longitude (and latitude) is required to convert 3D GPS vectors into 2D Local Horizon north and east components for 2D adjustments. They are also required when using GPS in 3D Local NEE networks.

    Always enter latitude and longitude in DD.MMSSsss format. When using GPS vectors in 2D or 3D Local NEE networks, be sure to provide the best possible approximate latitude and longitude, based on one of your 2D or 3D fixed stations.

  • Approx GHgt: When performing an adjustment based on orthometric height (elevation), you should consider providing an approximate geoid height for the project area. Internally, this approximate geoid height is added to the orthometric height for each station fixed in 1D or 3D to obtain an approximate ellipsoid height. This will minimize distance scaling issues on medium to large projects.

    All adjustment computations in Columbus are based on an ellipsoidal height-based model; therefore, approximating ellipsoidal height will produce more accurate results. For projects covering a small area, this improvement may be negligible: the adjusted heights will still be orthometric heights.

  • 1D Network Type: Specify the weight method for 1D Leveling networks using Height Difference observations. When weighting by number of setups or distance, the weight is calculated by the formula:

    wgt = 1.0 / num setups

    OR

    1.0 / distance.

    When weighting by standard deviation, the weight is computed identically to how it is done in 2D and 3D networks (for all observations):

    wgt = 1.0 / standard deviation squared

    OR

    wgt = 1.0 / variance.

  • GPS Parms: Set the Scale check box to scale GPS vectors, if applicable, during adjustment to better fit the existing control in the project. A minimum of two 2D control stations is required to perform scaling (or one 3D and one 2D, etc.).

    Set the Rotation check boxes to rotate GPS vectors, if applicable, during adjustment to better fit the existing control in the project.

    This requires a minimum of three control stations fixed in height and two control stations fixed in 2D. Some possible ways to satisfy include:

    • Three 1D stations fixed and two 2D stations fixed
    • Three 3D stations fixed
    • Two 3D stations fixed and one 1D station fixed
  • Misc
    • Ignore Apost Var: Select if you don’t want statistical results to be based on the A Posteriori Variance Factor. In most cases, you will not want this keyword set.
    • Ignore GPS Covar: Select to turn off the usage of the full GPS vector covariance matrix (3×3 matrix). Only the diagonal elements will be used.Normally, you will not set this check box. However, if you are comparing results against an adjustment where only the diagonal elements were used, then you should check this option.

    • Rotate Bearings: Select this option when you are using average bearings in your network. Average bearings need to be rotated back to true bearings (or azimuths) during adjustment. When set, all entered bearings are assumed to be average bearings, and they will automatically be rotated back to true bearings during adjustment. The rotation computation is based on the latitude of the project area.Public Land Survey System (PLSS) records are usually recorded with average bearing between corners. To incorporate these PLSS bearings into an adjustment (for example, 2D), they should be rotated back to true bearings by selecting this check box.

    • Sort By Absolute Value: Sort numeric grid columns by the absolute value of each field.
    • Rename Obs On Station Rename: When stations are renamed in the Data page, you will usually want observations with the same station name to be renamed, as well. If not, then de-select this option.

Reports tab

Use to select all reports you want to generate during network adjustment. Some reports may not be applicable to the adjustment you are currently performing; for example, Error Ellipsoids will not be generated when performing a 1D or 2D adjustment.