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When you calibrate survey data, you change the coordinates of the survey data from one coordinate system to another.
Survey CRS
As a rule, you calibrate data to get it onto your survey's CRS (Coordinate Reference System). You want everything on the same grid, so to speak.
•If your survey uses a State Plane projection, like NAD83, you want all the coordinates in your survey to be on that State Plane grid. You then use the appropriate Distance Type to display ground distances in COGO routines, drawings and traverses.
•If your survey doesn't use any kind of projection, it is considered to be a Local or Local Site CRS, using Cartesian coordinate computations. These coordinates inverse directly to distances measured on the ground at the site.
Example - Record Data
Let's say that you have entered all the record data for adjoining properties of a boundary survey using some basis of bearing (Uncalibrated coordinate system). But your survey uses a different basis of bearing (calibrated coordinate system).
•make duplicates of the record data traverses if you want to retain the original record bearings for future reference
•use the Calibrate command and select all the record traverses or their duplicates for the calibration
•tell TPC you want to create a new calibration and name it Record Data
•select point pairs where the record data and your survey refer to the same monuments
TPC will calibrate the selected traverses to your new basis of bearing. Depending on the calibration type you selected, record distances will also be scaled to fit your survey's CRS.
Example - Geodetic and Local Site
You can easily combine geodetic positions (Uncalibrated coordinate system) with local site coordinates (calibrated coordinate system) in TPC. This allows you to work with GPS / GNSS data in a familiar local site coordinates like 5,000 / 5,000.
To accomplish this, the survey's CRS still needs to be set to a State Plane or UTM type projection that converts between geodetic positions (LLh) and CRS coordinates (YXZ). These are your Uncalibrated coordinates. Then you apply a calibration to those CRS coordinates to change them to Local Site coordinates (calibrated coordinate system).
Working with Calibrated Survey Data
The survey data that just got calibrated, now acts as if it had been created at its new, calibrated position. In other words, it now works like any other calibrated data.
If you inverse between two calibrated survey points, you will get their calibrated inverse. If you compute a new point from them, you will get a new calibrated survey point. As a result, you will often calibrate once, then never think about it again.
Checking a Survey Points Calibration
By default, TPC underlines the coordinates of calibrated points in the Points Manager and Traverse View. You can then check to see which calibration is being used via the Survey Point Properties dialog or by turn on the Calibration column in the Points Manager.
Calibrating Survey Lines
If both endpoints of a survey are calibrated, TPC will also calibrate any distances stored with that line using the calibration's horizontal scale factor.
For example, if a curved line with a radius is calibrated, TPC will scale the radius of that line accordingly. For spiral lines, radii and spiral lengths will be calibrated.
Calibrating Points of Intersection
TPC stores curve data for Points of Intersection (PI's) in the traverses where the PI's are located. PI data can be a radius, tangent length or arc length, all of which are scaled by the calibration.
Protecting Calibrated Points
TPC will not calibrate protected survey points. Instead, it will list any protected points in the calibration report and let you know that they were not calibrated.
When TPC calibrates survey points, it does not protect them. However, you can then manually protect them via the Protect button in the Manage Calibrations dialog or sorting points by calibration in the Points Manager, then selecting the calibrated points and protecting them.
You can unprotect them later with the UnProtect button in the Manage Calibrations dialog.
Related Topics
Calibrating Data
Editions
Premium, Professional
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