Curve Tab

Select the Curve tab.

Figure 4:102. Edit Dialog - Curve Tab.

Adjust the vertices of the spline via the cursor

1. Select the Cursor Radio button then click the Offset Vertex button.

2. To adjust by a specified increment, select Coord, enter the increments in the U and V edit boxes and click Offset Vertex.

Insert knots in the current spline

3. Select Cursor and click the Insert button, then indicate the required position with the cursor

   OR select U or V and enter the appropriate value then click Insert.

Remove a particular knot interactively (using the cursor) from a curve

4. Select the Manual Radio button and click the Remove button.

Note: In general the removal of a knot will change the shape of the curve. However if Auto to Tol is selected and a tolerance entered in the edit box, on clicking Remove all possible knots will be removed from the spline so that it does not move more that the specified tolerance. This is especially useful for thinning out waterlines.

Align vertices can be used to straighten a curve by adjusting the coefficients of the B-Spline so they become co-linear. The user is prompted to select a start point and then an end point along the current curve, a window re-display will show the change. To achieve a straight line segment within a curve, two intermediate vertex points need to be between the two selected vertices.

An automatic fairing algorithm (based on the Eck and Hadenfield method) can be used to fair the current curve, by clicking the Auto Fair button. When automatic fairing takes place, vertices are moved such that energy in the curve is reduced. As a result, the size and irregularity of curvature tufts will also be reduced.

Both 2D and 3D curves can be faired using this method. Either the full curve can be faired or a region can be specified whereby the curve outside the specified region will not be changed. The region can be specified by giving lower and upper X, Y or Z values or by picking two positions on the curve with the cursor.

A tolerance must also be specified or the modified curve will not deviate from the original by more than the specified tolerance.