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# Learn the Shape Maker. Lines shaping.

Since most of the lines in Shape Maker form a wire frame on which to build surface patches, the shape of the lines is important for building smooth surface patches. Editing a control polygon of B-spline curves is a procedure described many times in various instructions. Therefore, we will analyze only some of the features and techniques inherent in Shape Maker. Example of complicated curve.

## Repositioning the endpoints of lines.

By default, all input lines are straight. The easiest way to modify a straight line is to change the position of its end points. Since the Shape Maker is always in edit mode, just left-click on the edited point and move it to a new position and once again click to fix the point in a new position, as shown below. Change endpoint position.

In this case, the editable point converges two topologically connected lines. Therefore, both lines followed the point when changing its coordinates.

## Editing a curve shape.

Very often, changing not only the position of its end points, but the shape of line itself is required. For this editing, just left-click on the line whose shape you want to change. Lines control polygon in edit mode.

The Shape Maker will show a control polygon for this line. Changing the shape of the control polygon will dynamically change the shape of the editable line. By default, a control polygon has two control points. The direction of the vector from the end point to the intermediate point of the polygon shows the angle of inclination of the curve to the end point, and the length of this vector indicates the degree of line fit to this vector at the end point. So if the vector is located horizontally or vertically, we will have a horizontal or vertical tangent at this point. Editing the points of the control polygon, you can try to achieve the desired shape of the curve. Changing curve shape by moving points of control polygon.

## Change the number of points of a control polygon.

Often ship curves are more complex than the curve shown above. Describing such curves requires more degrees of freedom. In our case, more control points are required.

There are several ways to add additional points to the control polygon. The easiest way is to click the left mouse button while holding down Ctrl on the line connecting the control points to each other. The system will add an additional control point to the control polygon. In this case, the shape of the curve does not change. If you need to reduce the number of points you need to right-click, while simultaneously pressing Ctrl, on the line between the control points. This method allows you to add a certain number of control points from the following series: 4,5,7,11,19,35,67. The reasons for using this series will be explained later.

You can also add and remove an arbitrary number of control points using the following command. Or from the Modify toolbar: In the dialog box, using the marked options, specify the required number of control points. An additional control point will provide more opportunities for changing the shape of the curve.Now we can change the shape of the curve while maintaining the slope angles of the start and end points. Extra point in control polygon. Lines shape changes with keeping tangency in endpoints.

## Defining tangents at the end points of a curve.

Quite often, it becomes necessary to establish tangents at the start and end points of the line strictly horizontally or vertically.To do this, just left-click with the pressed Ctrl button on the line between the end point and the first control point of the polygon.In this case, the tangent will be set horizontally or vertically depending on the initial angle of inclination of the tangent at this point.If the angle of inclination is less than 45 °, the tangent will be horizontal, if more - vertical. Orthogonal tangents in endpoints.

The same can be done by calling the appropriate command from the menu. Or from the Modify toolbar: