This command allows you to calculate coordinates of an unknown instrument setup point given the angles and distances from up to twenty distinct reference points. The reference points are recalled from your working job file. If a control file is active in Job Settings, and the entered point ID is not found in the current working coordinate file, then the point will be recalled from the control file automatically. You can also access points from the control file by using the from list icon.
Direct and Reverse measurements can be activated within the Configure screen in Resection. The options within Configure expand (eg. for "Auto Turn" capability) if you are using motorized or robotic total stations versus conventional total stations. If you choose Direct & Reverse, then the reverse measurements count as part of the 20 allowable measurements, so the maximum number of reference points becomes 10. As long as you have at least two distinct points, you can shoot the same point twice or more with a direct or D&R measurement.
Elevations can be ignored on any measurement. Angle Only Readings can be mixed in as well. This is useful when sighting radio towers and church steeples with known coordinates. In fact, all of your resection points can be measured by angle only, in which case 3 or more points are necessary for an accurate calculation. Sometimes if the 3 angle only points are in the same quadrant of view, a solution won't be found, requiring additional points. When elevations are used, measurements will contribute to the calculation of the setup point elevation. After entering the routine, the first screen appears as follows:
The points can also be selected from the point list or directly from the map screen by pressing either the list or map icons. You will also be prompted for the Instrument Height and a Target Height. On reading #1, you will be asked if you want to Set Zero on the first resection point (optional).
If you press Configure, you can set standard errors for the measurements, as shown below. These settings allow you to take advantage of network least squares and weighting in the calculation performed by SurvCE. The default values are shown. You can also enable Direct & Reverse measurements here, in addition to using EQUIP, Configure.
Press Read when you are ready to take a measurement. The angle right, zenith angle, and slope distance are recorded.
Repeat this process for all measurements of the resection. After the second measurement, there is enough information to conduct the resection calculation, so the Calculate button at the top of the dialog becomes active and can be selected. If you select Calculate, you can review the data, then return to taking more shots by hitting Cancel rather than OK, which would prompt to store the point.
Any time Calculate is selected, the Review Resection screen appears. The input data is displayed in a list structure, and you have the ability to turn certain measurements on/off and recalculate the solution, without the necessity of re-measurement. You can also edit point numbers, instrument and rod heights, and more here. When satisfied with your edits and the solution, you can store the results of the resection.
Since there is redundant data, the final calculated coordinate differs slightly from the individual measurements. The command reports the calculated coordinate’s northing, easting, and elevation, and the difference between the calculated coordinate and the individual solutions as residuals, which indicate the quality of the data. High residuals suggest a problem with the input data. If you select the red X in the Review Resection Screen, you are returned to the Read screen in case you want to collect more shots. Here in the Read screen you can truly Cancel if that is your intention. Shown here is a resection to 2 points using D&R (direct and reverse), with angle only in the reverse face. Note that even in a 2-point resection, a closure calculation is presented.
In the “Store this Point?” dialog box shown below, you are prompted for the point number and description of the calculated point (the occupied station/setup point). With three or more resection points, residuals are presented showing the accuracy of the calculation. When you press OK from the "Store this Point?" dialog, you will be setup on the calculated point backsighting the first point shot in the resection.