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Calibration types are based on the type of coordinate transformation used.
Changing Calibration Types
You can change the type of a calibration in the Results tab of the Calibration Properties dialog.
This dialog displays the calibration types listed here without the 2D or 3D qualifier. Instead, TPC selects the appropriate 2D or 3D calibration based on your corresponding Vertical calibration type (None, Shift Only or Shift + Plane).
Vertical Calibration Types
The Vertical calibration type determines whether TPC does a 2D or 3D calibration. The difference is that for a 3D calibration, positions can be modified about all three axes (X, Y and Z) whereas for a 2D calibration, positions are modified only in the X/Y plane with the elevation being modified independently, if at all.
None
Elevations will not be calibrated.
Shift Only
TPC will compute the average change in elevation and apply it to each calibrated point.
Shift + Plane
TPC will switch from a 2D calibration of the type you selected to a 3D calibration of that same type.
3D calibrations rotate about all three axes (X, Y and Z), creating a 3D plane to which elevations are calibrated.
2D Conformal
In this calibration, TPC scales, rotates and translates X/Y coordinates only, using a single horizontal scale and rotation about the Z-axis. Elevations are not calibrated.
Because it is conformal, the shape (relationship of the coordinates to each other) of the coordinates does not change.
Elevations are modified based on the Vertical type only.
3D Conformal
In this calibration, TPC scales, rotates and translates X, Y and Z.
TPC uses the 3D Conformal instead of the 2D Conformal when you change the Vertical calibration type to Shift + Plane.
Because it is conformal, the shape (relationship of the points to each other) of the points being calibrated does not change.
Because the calibration involves rotation about all three axes, the result can be thought of in terms of a 3D plane. So this is a good calibration to use for 3D point cloud or photogrametric data.
2D/3D Translate Only
Translate Only performs an average translation based on the number of control (target) points. No scale or rotation are applied.
This is the only calibration that can be computed from a single Uncalibrated/control point pair.
2D translates only the X/Y values, while 3D translates X/Y/Z values.
2D/3D Scale Only
Scale Only computes the scale per the associated 2D/3D Conformal calibration type, then sets the rotation and translation to zero. You might compute this calibration type just to get the scale factor for another use.
A 2D Scale Only is the kind of calibration TPC does in the Convert Coordinates and grid<=>ground routines. This conversion always requires a base point about which everything is scaled toward or away from. Because of this, TPC computes the average position of the Uncalibrated points and uses it as the base point in this calibration. You can think of this as scaling survey objects in place. Once scaled, you can still rotate and translate it as needed.
2D/3D Scale and Rotate
TPC uses this calibration internally when it creates block references in a drawing. The original block is scaled and rotated to produce a block reference.
Like the scale only calibration type, think of this as doing an in place calibration on the selected objects where the base point is the average position of those objects. So when applied, the calibrated objects will appear to scale and rotate in place and can then be translated if needed.
2D Affine
In this calibration, TPC scales, rotates and translates X/Y coordinates only, using separate X and Y scales and rotation about the Z-axis. Elevations are not calibrated.
It is not conformal, so the shape (relationship of the points to each other) of the points is allowed to change.
3D Affine
In this calibration, TPC scales, rotates and translates X/Y/Z coordinates, using both a horizontal and vertical scale.
TPC choose uses 3D Affine instead of the 3D Affine when you set the Vertical calibration type to Shift + Plane.
It is not conformal, so the shape (relationship of the coordinates to each other) of the coordinates is allowed to change.
Reference
Although coordinate transformation are covered widely in academics, TPC has relied heavily on the book adjustment computations Spatial Data Analysis fifth edition by Charles D. Ghilani, copyright 2010 John Wiley & Sons, Inc.
Related Topics
Calibrating Data
Editions
Premium, Professional
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