Balancing coordinates is also referred to as Adjusting coordinates.
•From the Closure View, choose Tools | Balance Coordinates. TPC displays the Adjust Coordinates dialog.
•Select the options you want and choose OK.
When you balance a traverse, you force the mathematical closure of the traverse through the control points in the traverse, starting with the Initial point (From) and ending with the Closing point (To). Some amount of adjustment is systematically applied to each control point being balanced so that the Closing point ends up at a predetermined position.
In the case of a closed loop, this is the Beginning point. In the case of a closed point-to-point traverse, this can be any known point or coordinate.
Only the points between the Beginning and Closing points will be adjusted. These are referred to as the Closing Points. . The Initial point itself is not adjusted, but the Closing point is.
Once the control points are adjusted, any side shots originating from them are recomputed using the raw data. The side shots are not adjusted; they are simply recomputed from the adjusted control point using the raw data.
Note: If the traverse you are adjusting includes sideshots that are not computed via raw data in that travese, these sideshots will not be updated based on their adjusted control points.
Viewing Balanced Coordinates
Coordinates are balanced from the Closure View. If you balance coordinates in the Closure View and then return to its Traverse View, you will see the adjusted coordinates and the inversed angles, bearings and distances displayed in the view.
Methods
We strongly encourage you to become familiar with both the strengths and weaknesses of these adjustment methods before putting any of them to use.
Compass Rule
The Compass Rule states that the correction to be applied to the lat/dep of any course is to the total correction in lat/dep as the length of the course is to the length of the traverse.
It assumes that the errors in traversing are accidental and vary with the square root of the lengths of the sides. It also assumes that the effects of errors in angular measurements are equal to the effects of errors in distance measurements.
Transit Rule
The Transit Rule states that the correction to be applied to the lat/dep of any course is to the total correction in lat/dep as the lat/dep of that course is to the arithmetical sum of all the lat/dep of the traverse.
It assumes that errors in traversing are accidental and that the effects of errors in distance measurement are greater than the effects of errors in angular measurements.
Crandall Rule
The Crandall Rule approximates a least squares adjustment to the length of each course. It assumes that the effects of errors in angular measurements are negligible or have already been adjusted out of the traverse. It further assumes that any adjustment should be applied only to the lengths of the courses.
Restoration of Lost Corners - PLSS
Professional Edition Only
The following adjustments (Irregular Boundary, Grant Boundary and Angle Points of Meander Lines) pertain to restoring lost corners in the Public Lands Survey System (PLSS). They involve adjustment to record data based on retracement data.
In TPC, you will enter the record data into a traverse (record traverse) and adjust it as a closed point to point where the correct closing point is the retraced position of the final point of record.
Example: 'Record' traverse with points R1, R2, R3, R4 & R5. 'Retrace' traverse with points T1, T2, T3, T4 & T5. Where T5 is the retraced position of R5.
You will adjust the 'Record' traverse so that it's closing point, R5, ends up at the same position as T5 after the adjustment. To accomplish this, T5 is recalled as the correct closing point in the point to point adjustment of the Record traverse.
Adjustment Details
If you turn on Adjustment Details, TPC will display the appropriate parameters and individual course adjustments as if you had done the adjustment manually. This will allow you to compare TPC results with similar adjustments from CMM or other methods.
Irregular Boundary Adjustment
TPC implements this adjustment as described in Manual of Surveying Instruction 2009, page 174, section 7-51. Figure 7-8 gives the wrong formula for this adjustment, so you will want to check for the appropriate addenda to the manual. See Irregular Boundary.
Grant Boundary Adjustment
TPC implements this adjustment as described in Manual of Surveying Instruction 2009, page 176, section 7-54. See Grant Boundary.
Angle Points of Meander Lines
TPC implements this via the Compass Rule adjustment as described in Manual of Surveying Instruction 2009, page 176, section 7-53.
Summary of Methods of Balancing a Survey
The discussion relating to methods of balancing a survey may be summarized by the following statements:
•In many cases a careful, arbitrary distribution of errors on the basis of a knowledge of the field conditions is the best that can be made.
•If systematic errors are believed to be present in the linear measurements, they can be eliminated only by applying the proper computed corrections to the field measurements before any rules for balancing the survey can be applied, since systematic errors are not subject to distribution by any general rule.
•If the error of closure is subject to accidental errors affecting angular and linear measurements equally, the Compass Rule is valid.
•In most cases, the Transit Rule cannot properly be used.
•If accidental errors in linear measurements are assumed to be much larger than those in angles, the Crandall Method is Valid.
Davis & Foote, Surveying, Fourth Edition
You cannot adjust coordinates if raw data does not exist. For more information on raw data refer to the Update Raw Data command in the Traverse View.
Balancing Elevations
TPC assumes that the correction to be applied to the elevation of any point is to the total correction in elevation as the distance along the traverse to the point is to the length of the traverse.
Precision
Warning!! You can get different results (adjusted coordinates and closure) depending on whether you apply precision before or after adjusting coordinates. If precision is applied before coordinates are adjusted, the adjustments are based on the rounded raw data values and so the closure error will probably not be zero. If precision is applied after adjustment, the adjustment is based on the raw data and the resulting inverses are then rounded based on the precision.
Scale Factor
If you plan on apply a scale factor adjustment, you will want to apply the scale factor first. This allows TPC to adjust the scaled positions properly.
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