Selects a control file, which identifies the known transformation points. It is possible to either key in the file or select a file by clicking the browse button. Warp control files are generated using the Control Points dialog (see Define Control Points).

Selects which optional conditions control the transformation. The following are selectable:

• Transformation option.

• Weighting option.

• Number of control points option.

• Master file elements option.

Affine — Selects the affine transformation. The affine transformation uses the following set of normal equations to approximate x',y' given x and y:

A(x,y) = x' = c1 * x + c2 * y + c3

B(x,y) = y' = c4 * x + c5 * y + c6

The 6 coefficients are calculated by solving a system of 6 linear equations of the partial derivatives with respect to each of these coefficients and using the control points to substitute for x,y and x',y'.

The drawback to the Affine transformation is that though it minimizes the distance in x and the distance in y, it does a poor job in the overall distance minimization.

Conformal — Selects the conformal transformation. The conformal transformation uses the following set of normal equations to approximate x',y' given x and y:

A(x,y) = x' = c1 * x - c2 * y + c3

B(x,y) = y' = c2 * x + c1 * y + c4

The 4 coefficients are calculated by solving a system of 4 linear equations of the partial derivatives with respect to each of these coefficients and using the control points to substitute for x,y and x',y'.

The Conformal transformation does a slightly better job of minimizing distances than the Affine, but may produce results with irregularly spaced control points.

Uniform Least Squares Fit — Minimizes the distance between target points and transformed source points using Least Squares. This is the default and the most rapid transformation if the Use All Control Points option is also specified. A drawback to this method is that all elements within the fence are transformed with the same parameters, regardless of control point density or spacing. This method may provide poor results with irregularly spaced control points.

Apply Inverse Distance Weights — Minimizes the distance between target points and transformed source points using Inverse Distance Weights. This option ensures that control points nearest an element weigh more heavily in the transformation than control points in the distance. This method is significantly slower than the uniform method since transformation parameters must be recalculated for each point being transformed. The error residual between target control points and transformed source points is zero. This method may actually transform a set of collinear lines into a set that resembles a curve.

Use all Control Points (default) — Specifies that all control points are used to determine transformation parameters.

Specify Number of Control Points — Specifies the number (four or fewer) of closest control points to use in determining transformation parameters. Selecting this option may slow down processing time, but it ensures that control points nearest an element will weigh more heavily in a transformation than points in the distance. This option is most useful when there are a large number of evenly spaced control points.

Copy — Makes a copy of each transformed feature.

Move — Moves each transformed feature. If the elements being transformed are in a reference file then the effect will be to copy and move those elements to the active file.

Stretch — Provides an analog to MicroStation's Fence Stretch command. Only the vertices inside the fence (or outside of a void fence) are transformed. This allows the application of the transformation to only part of an element.

Previews a transformation prior to changing a design file. If on, the transformed elements are display-only and are not actually transformed.

Used to specify the number of control points, when Specify Number of Control Points is selected as above. This box will not accept a number less than 4. When Specify Number of Control Points is not selected, this box is greyed.

Opens the Control Points dialog. See Define Control Points.

Executes the geometric transformation specified in the Warp Projection dialog.