Drawing Curves

Function Description

The application supports various curves, including Bezier curve, B-spline curve, Cardinal curve, free curve, and geodesic.

Function Entry

  • Features tab -> Objects group -> Line drop-down list -> Curve.

Operating Instructions

Drawing Bezier Curve

A Bezier curve is controlled by two start nodes and two end nodes not lying on the curve, which determine the curve's direction, while other control points on the curve are used to fit the intermediate points of the curve. At least six control points are required to complete the drawing of a Bezier curve segment.

  1. In the Objects group of the Features tab, click the Line drop-down button and select the Bezier Curve option. The Bezier curve cursor appears.
  2. Move the cursor to the map. You can see that as the mouse moves, the coordinate values of the current mouse position are displayed in real-time in the following parameter input boxes. Enter the coordinate values of the first control point of the Bezier curve in the parameter input box (you can switch between the two parameter input boxes by pressing the Tab key) and press Enter to confirm.
  3. Input the coordinates of the second to fourth control points in the same way. The coordinates of the first four control points determine the direction of the Bezier curve.
  4. Input the coordinates of the fifth control point on the curve. At this point, a blue dashed line will appear between the third and fourth control points, which is the first fitted segment of the Bezier curve.
  5. Continue to input the coordinates of the sixth control point to draw the second segment of the Bezier curve.
  6. Repeat the previous step to continue drawing other segments of the Bezier curve.
  7. Right-click to end the current drawing.

B-spline Curve

A B-spline curve is drawn using the first and last control points on the curve, along with other intermediate control points that are not on the curve. All other points on the curve are fitted based on the intermediate control points on the curve. At least four control points are required to complete the drawing of a B-spline curve segment.

  1. In the Objects group of the Features tab, click the Line drop-down button and select the B-spline Curve option. The B-spline curve cursor appears.
  2. Move the cursor to the map. You can see that as the mouse moves, the coordinate values of the current mouse position are displayed in real-time in the following parameter input boxes. Enter the coordinate values of the first control point of the curve in the parameter input box (you can switch between the two parameter input boxes by pressing the Tab key) and press Enter to confirm.
  3. Enter the coordinates of the second control point on the curve.
  4. Enter the coordinates of the third control point on the curve. At this point, a blue dashed line will appear between the first and third control points, representing the first segment of the B-spline curve.
  5. Enter the coordinates of the fourth control point on the curve. At this point, a blue dashed line will appear between the third and fourth control points, representing the second segment of the B-spline curve.
  6. Repeat the previous step to continue drawing other segments of the B-spline curve.
  7. Right-click to end the current drawing.

Cardinal Curve

A Cardinal curve is drawn by determining the control points on the curve, and the other points of the curve are fitted based on all control points. At least three control points are required to complete the drawing of a Cardinal curve segment.

  1. In the Objects group of the Features tab, click the Line drop-down button and select the Cardinal Curve option. The Cardinal curve cursor appears.
  2. Move the cursor to the map. You can see that as the mouse moves, the coordinate values of the current mouse position are displayed in real-time in the following parameter input boxes. Enter the coordinate values of the first control point of the curve in the parameter input box (you can switch between the two parameter input boxes by pressing the Tab key) and press Enter to confirm.
  3. Enter the coordinates of the second control point in the same way. You will see a blue dashed line appear between these two points.
  4. Move the mouse and enter the coordinates of the third control point. You will see a second blue dashed line appear between the second and third control points.
  5. Right-click to end the current drawing.

Free Curve

A free curve is a segment of curve obtained by freehand dragging. Drawing a free curve is very useful for creating irregular boundaries or when tracing with a digitizer.

  1. In the Objects group of the Features tab, click the Line drop-down button and select the Free Curve option. The free curve cursor appears.
  2. Move the cursor to the location where you want to create the free curve. Click and hold the left mouse button, then move the mouse to draw a curve on the map that matches the cursor's movement trajectory.
  3. After completing the drawing, right-click to end the operation.

Geodesic

A geodesic is a curve that follows the curvature of the Earth's surface and can most accurately represent the shortest distance between any two points on the Earth's surface. It is commonly used for drawing global maritime or aviation routes. Global Pan must be enabled to perform geodesic drawing operations.

The following example of drawing an aviation route details the operational steps of this function:

  1. Open the "World.smwu" workspace in the sample data, open the "world map_Day" in the map, add the route line dataset to the map, and enable editing for the line data.
  2. In the Objects group of the Features tab, click the Line drop-down button and select the Geodesic option. Move the mouse to the map to start drawing.
  3. Click the left mouse button at the starting point and ending point of the route. After drawing is complete, right-click to end the current line object. After drawing, set the layer style to obtain the following result:
Figure: Route Map