Application: gvSIG desktop

import org.gvsig.fmap.geom.operation.GeometryOperationException;

import org.gvsig.fmap.geom.operation.GeometryOperationNotSupportedException;

 * This interface is equivalent to the GM_Arc specified in <a href=

 * "http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=26012"

 * >ISO 19107</a>. A Arc is defined by 3 points, and consists of the arc of the

 * circle determined by the 3 points, starting at the first, passing through the

 * second and terminating at the third. If the 3 points are co-linear, then the

 * arc shall be a 3-point line string, and will not be able to return values for

 * center, radius, start angle and end angle.

 *

 * @see <a

 *      href="http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=26012">ISO

 *      19107</a>

    /**

     * Sets the three points to define an arc.

     * These are three ordered points that belong to the arc

     * (none of them is the center of the ellipse/circle). Therefore

     * they must not be aligned.

     *

     * @param startPoint

     *            The start point of an arc.

     *            The middle point of an arc.

     * @param endPoint

     *            The end point of an arc.

     * @exception IllegalArgumentException

     *                if the three points are aligned or

     *                there is a repeated point.

     *

     */

    void setPoints(Point startPoint, Point midPoint, Point endPoint);

    /**

     * Sets the values to define an arc.

     *

     * @param center

     *            The center of the arc.

     * @param radius

     *            The radius.

     * @param startAngle

     *            The start angle of the arc (in radians)

     * @param angleExt

     *            The angular extent of the arc (in radians).

     *

     *            The sign convention is:

     *

     *            startAngle = 0 is "3 o'clock";

     *            startAngle = (PI / 3) is "1 o'clock";

     *            angleExt > 0 means "advancing clockwise";

     *            angleExt < 0 means "advancing counterclockwise".

     */

    void setPoints(Point center, double radius, double startAngle, double angleExt);

     * @param center

     *            The center of the arc.

     * @param radius

     *            The radius.

     * @param startAngle

     *            The start angle of the arc (in radians)

     * @param angleExt

     *            The angular extent of the arc (in radians).

     *            The sign convention is:

     *

     *            startAngle = 0 is "3 o'clock";

     *            startAngle = (PI / 3) is "1 o'clock";

     *            angleExt > 0 means "advancing clockwise";

     *            angleExt < 0 means "advancing counterclockwise".

    void setPointsStartExt(Point center, double radius, double startAngle, double angleExt);

     * @param center

     *            The center of the arc.

     * @param radius

     *            The radius.

     * @param startAngle

     *            The start angle of the arc (in radians)

     * @param endAngle

     *            The end angle of the arc (in radians).

    void setPointsStartEnd(Point center, double radius, double startAngle, double endAngle);

    /**

     * Return the first point that has been used to create the arc.

     *

     * @return

     *         The first point of the arc.

     */

    Point getInitPoint();

    /**

     * Return the end point that has been used to create the arc.

     *

     * @return

     *         The end point of the arc.

     */

    Point getEndPoint();

    /**

     * Return the center of the arc, that is, the center of the ellipse/circle

     * in which the arc is based.

     *

     * @return The center of the arc.

     */

    Point getCenterPoint();

    /**

    /**

     * Returns the counterclockwise angle formed by the horizontal line passing

     * through the center, the center itself and the starting point.

     *

     * @return

     * @throws GeometryOperationNotSupportedException

     * @throws GeometryOperationException

     */

    double getStartAngle() throws GeometryOperationNotSupportedException, GeometryOperationException;

    /**

     * Returns the counterclockwise angle formed by the horizontal line passing

     * through the center, the center itself and the ending point.

     *

     * @return

     * @throws GeometryOperationNotSupportedException

     * @throws GeometryOperationException

     */

    double getEndAngle() throws GeometryOperationNotSupportedException, GeometryOperationException;

    /* (non-Javadoc)

     * @see org.gvsig.fmap.geom.primitive.Arc#getStartAngle()

     */

    public double getStartAngle() throws GeometryOperationNotSupportedException, GeometryOperationException {

        return getAngle(getCenterPoint(), getInitPoint());

    }

    /* (non-Javadoc)

     * @see org.gvsig.fmap.geom.primitive.Arc#getEndAngle()

     */

    public double getEndAngle() throws GeometryOperationNotSupportedException, GeometryOperationException {

        return getAngle(getCenterPoint(), getEndPoint());

    }

    private double getAngle(Point start, Point end) throws GeometryOperationNotSupportedException, GeometryOperationException {

        double angle = Math.acos((end.getX() - start.getX()) / start.distance(end));

        if (start.getY() > end.getY()) {

            angle = -angle;

        }

        if (angle < 0) {

            angle += (2 * Math.PI);

        }

        return angle;

    }