The Adjust page is where you perform interactive adjustments and view results. Adjustments are "interactive" because when you make UI changes, the network adjustment results may change. You must select a project to be active before you can access the Adjust page.
The Adjust page provides several choices that can be made prior to adjustment, including:
The Left Grid contains a list of all stations currently defined within the project. Depending on the adjustment type, each station will occupy from one to three rows in the grid. Within this grid, you can remove individual stations from the adjustment and, depending on the adjustment type, fix one or more coordinate components for each station.
For example, for a 3D Lat, Lon, Hgt adjustment, each station can be fixed (or not) in Latitude, Longitude and/or Height.
- To fix a station in three dimensions, select the Lat, Lon, Hgt to be fixed.
- To fix a station in Height only, you simple fix the Hgt component for that station.
The Right Grid shows all the current observations that are applicable to the stations selected to be in the network in the Left Grid. If you remove a station from the network in the Left Grid, any observation tied to this station will be removed from the Right Grid.
Design works when the quality obtained in the field is as good or better than what you designed.
You can either perform an Adjustment of existing field data (the most common scenario) or evaluate the Design (Pre-Analysis) of a network that has not yet been measured.
Network design allows you to determine the statistical results you can obtain in the field—before you even make a measurement. By working with three variables, you can design a network that will help you minimize field costs, while achieving the quality standards specified for the project.
The three variables are:
- Number of stations and their location (given by coordinates)
- Types of measurements: GPS dX, dY, dZ, hor angles, directions, slope distances (chord), etc.
- The expected standard deviation (or standard error) for each measurement type
- Tell Columbus the stations to use, along with their approximate coordinates.
- Indicate the observations that will be observed at each station (including station names and observations). Since you have not measured the observations yet, you simply enter a number such as 1.0 for the observation value.
- For each observation, provide the expected standard deviation that you expect to meet in the field—just like you would do for an adjustment.
As you can see, the data entry for Adjustment vs. Design is nearly identical. However, Design cannot compute the approximate coordinates, since you have provided no real observation values. Therefore, you must provide the approximate coordinates for each station (in 1D, 2D, or 3D, depending on the network type).
When you click Start, all the usual network adjustment statistics will be computed for your review. These statistics are a function of the location of the stations (approx coords), the observation types used and the expected error of the observations. If the resulting statistics (distance errors, ALTA results, 2D error ellipses, etc.) don’t meet the project requirements, keep tweaking your design until they do.
For example, you may do one or more of the following to improve your design results:
- Use more accurate total station, thereby allowing you to set your design standard deviations to smaller values
- Add GPS vectors to minimize network geometry issues
- Strengthen the geometry of a conventional network by avoiding small angles
- Add more observations to increase the number of cross-ties to other stations, thereby increasing redundancy
Later, when you do the field work, if you set your stations at the designed locations, measure the designed observations and achieve the quality of the designed standard deviations, you are guaranteed to get a final adjustment that meets your project quality requirements (after removing any blundered observations).
Note: When using the Adjust by File (adjusting from a file), insert the following keyword near the top of the input file
The Left Grid shows stations that have actual station records. These station records can be set up or changed in the Data page, Stations tab.
In order to save time, you may decide to only define station records for stations you intend to hold fixed in the adjustment (in order to define their known coordinate values). Only defined stations show up in the Left Grid. When Create Station is unchecked, only observations tied to stations in the Left Grid will be displayed in the Right Grid (see below).
However, you can tell Columbus to display all observations by selecting the Create Station check box. In fact, this (checked) is usually the preferred setting. When you start the adjustment, Columbus will create the missing station records (with default coordinates) and perform the adjustment.
So why would you ever want to uncheck the Create Station option? There is one possible side-effect of always enabling this field: When setting up your observations, you may have misspelled a station name. For example, if you have a zenith angle pointing to station BBb, but you really intended to name the station BBB, you would end up with two different station names representing the same point on the ground (BBb and BBB). With Create Station enabled, Columbus will ensure that both stations are created during adjustment. This will lead to adjustment problems that could be time-consuming to solve (especially for a network with dozens of stations).
In summary, using this option means you don’t need to explicitly define all your stations with station records. While this is very convenient, just be careful that all your observations reference the correct station names.
Here you select the adjustment type. The options are:
- 1D Hgt: Used for traditional leveling and trig leveling surveys. Stations fixed in 1D should be provided with their known hgt.
- 2D Local N, E: 2D adjustment using local plane coordinates. These projects should be limited to one square kilometer. Stations fixed in 2D require known local north and east values.
- 2D Grid N, E: 2D Grid (State Plane) project. Stations fixed in 2D require known grid north and grid east values.
- 2D Lat, Lon: 2D geodetic project based on latitude and longitude. Stations fixed in 2D require known latitude and longitude.
- 3D Local N, E, Hgt: 3D adjustment using local plane coordinates. These projects should be limited to one square kilometer. Stations fixed in 3D require known local north, east and hgt.
- 3D Grid N, E, Hgt: 3D Grid (State Plane) project. Stations fixed in 3D require known grid north, grid east and hgt.
- 3D Lat, Lon, Hgt: 3D geodetic project based on latitude, longitude and hgt. Stations fixed in 3D require known latitude, longitude and hgt.
When you select an adjustment type, data in the Right Grid will be updated to reflect only observations applicable to that adjustment type (for example, GPS observations will not appear if the 1D Hgt adjustment is selected).
There are two different height values for each station record (see Data page, Stations tab). You can either use the Orthometric height during adjustment or the Ellipsoidal height. When the adjustment begins, any station fixed in height will be assigned the corresponding known height value from the station record (ortho height or ellipsoidal height).
2D Station Height
Select this checkbox to perform a 2D adjustment where you wish to hold the height of each station fixed at its estimated value. The estimated or known value must be defined in the station record (see Data page, Stations tab). This option is often used when you are performing a 2D adjustment in an area in which the terrain (heights) vary considerably and using a simple mean project height may not be sufficient.
This is an "all-or-nothing" proposition. If you choose to use this option, you will need to provide an approximate height for every station in the network. Scaling from a topographical map will usually be sufficient to get estimates within +/- 5 to 50 meters. Be sure to enter these approximate heights in either the Orthometric or Ellipsoidal height field (depending on the Height Type selected above) of the station record.
2D Mean Height
Enter a value in this field when you intend to perform a 2D adjustment at an average project height. You must also uncheck the 2D Station Height checkbox. This 2D option is more commonly used than the 2D Station Height option above. It simplifies adjustment setup and can deliver excellent 2D results in areas in which the terrain does not vary much. Try adjustments at several different mean heights to compare results.
After an adjustment is completed, you can view the adjustment summary and individual results in the Result tabs. You can sort grids by columns, generate reports, and keep adjusted coordinate values into project memory.