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Step 1 – Analyze
Overview : Step 1 - Analyze -----> Step 2 - Solve -----> Step 3 - Report -----> Step 4 - Update
In this step, you build the Least Squares data which will be used when solving the network, then edit it to make sure it contains the points and observations you want.
When you open this dialog, TPC first searches for existing Least Squares data. This data is stored in a file with the extension .LSA. If found, TPC loads the file and recreates your last analysis, complete with raw coordinates and observations. The most recent analysis will appear in the "Review Current Analysis" box. If no data has been analyzed for this survey, the box will display "No data available".
A typical sequence in analyzing a survey would be
•Select the options you want from the pull down What list, like Entire Survey, Selected Traverses, or Tagged Traverses.
•Edit the Points, specifying the appropriate precisions and including just the points you want.
•Edit the Observations, specifying the appropriate precisions and including just the observations you want.
•Press the Analyze button to ensure you're working with your most-recent selections.
Once you are satisfied with the data that is included in the analysis, proceed to Step 2 – Solve.
Analyzing a Survey
TPC analyzes the selected traverses in your survey to create a Least Squares network with the appropriate point and observation records. You can analyze all the traverses in the survey, creating a network for the whole survey or you can analyze selected traverses, creating a partial network.
Each survey can have only one Least Squares network associated with it. This Least Squares data is stored in a separate ASCII text file with the extension .LSA. So the survey JOB1.TRV would have a JOB1.LSA network file. See Least Squares Files.
Analyzing a Traverse
When you adjust a traverse using Least Squares, TPC analyzes just that traverse. TPC considers the closing points and angles you entered in the Closure View along with all the control points in the traverse. If you included the closing point and closing angle as the last two points in the Traverse View, TPC will use this data instead of the closing angle you enter in the Closure View.
Each traverse can have only one Least Squares adjustment associated with it. The Least Squares data is stored in a separate ASCII text file using the traverse name as the filename and the extension .LSA.
Standard Error Estimates (default)
When generating observations from survey data, TPC uses the estimates of standard error established for this analysis in the Miscellaneous tab.
You will want to select estimates of standard error that are appropriate for the equipment and methods used in your survey.
Standard Error Estimates by Traverse
You can also assign aPriori values to a traverse. When TPC generates observations from that traverse, it will use the estimates of standard error of the traverse instead of survey's.
•To generate aPriori values for a traverse, go to the Traverse View for a traverse and choose Tools | Least Squares Standard Errors...
•To generate aPriori values for multiple traverses, go to the Traverses Manager, select the traverse you want to set and choose Tools | Least Squares Standard Errors...
In steps 1 and 2, you can also remove the aPriori values for a traverse(s), in which case TPC will revert back to the aPriori values for the least squares analysis for these traverse observations.
Including Survey Points
When TPC searches a selected traverse, it looks for control points that are being computed. These are automatically included in the analysis. TPC also looks for control points that are needed to compute points that have been included. If an observation that includes a horizontal angle references a backsight point that has not yet been included, TPC adds that backsight point. The Least Squares solution requires that observed data be compared to inversed data, so the reference points must be present in the analysis.
TPC allows you to specify the standard error of their coordinates values, to accommodate varying levels of control.
Including Protected Points
If a protected survey point is included, TPC must determine whether or not this point should be ‘fixed’. Remember, a fixed point is not allowed to move in the Least Squares solution. TPC relies on the ‘Fix Protected Points’ option in the Analyze dialog. to determine whether or not to fix protected points.
Computed vs Coordinate Points
When analyzing survey points for Least Squares, TPC determines if the related points have been computed by the observations being analyzed or if those points were given coordinates.
Computed Points
TPC sets the standard error estimate of these points to 0.0, meaning they are free to be computed by the Least Squares solution. You can also think of these computed points a being unweighted.
Of course, you can assign a precision to any point prior to solving, but as TPC analyzes the survey, it will set them to 0.0.
Coordinate Points
Coordinate points, points that are not being computed by the Least Squares solution, have their standard error estimates set by the aPriori values in the Standard Errors dialog.
These aPriori estimates allow you to easily weight points who coordinates may have errors you want to account for. An example of this would be RTK points collected using GNSS. If you collect RTK points that are near to their base station or virtual reference station, you will probably expect them to be weighted higher (more accurate) than RTK points that are collected farther away form their base station or virtual reference station.
Including Observations
TPC adds observations based on the raw data stored in the selected traverses. A foresight observation in a traverse, will create a horizontal angle record and a horizontal distance record. If the 3D option is selected, a vertical angle or vertical distance record will also be added.
If you traversed to the same point more than once (it is included as a foresight in more than one selected traverse), TPC will create additional observation records each time it is encountered. The point itself is only included once, so the extra observations create what is called ‘Redundancy’.
Including Redundant Observations
TPC allows you to recall an existing point into a traverse then enter observed data like a distance or angle to that point. In this special situation, the observed data does not recompute the observed point. It simply creates what is called ‘Redundancy’. Your traverse or survey can include any number of redundant observations. As a rule, the more redundant observations you include, the stronger (more accurate) the solution.
Side Shot Points are Not Included
Side shot points are not included. Instead, TPC provides an option to re-compute them when you update the survey or traverse with the adjusted (computed) coordinates. This option is available in the Update page.
Related Topics
Least Squares
Least Squares Network Adjustment
Redundant Data
Editions
Premium, Professional
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