Arc: 3 Points

Tool to create an arc that goes through 3 points. Click Create > Arc and choose from these available options in the drop-down menu.

 

3 Points constructs an arc beginning at the first point , passing through the second, and ending on the third point. As you construct the arc, you will see it "rubber-banding" on the screen.

  1. Select 3 Points.
  2. Click the position where the arc is to start.
  3. Click a position anywhere on the arc.
  4. Click the end position for the arc.

This diagram shows arcs constructed using 3 Points. In all cases, points 1 (start of arc) and 2 (point on the arc) are the same. Point 3 (end of arc) then fixes the radius and length of the arc:

Angle, Centre, Point constructs an arc through a given angle around a known centre point.

  1. Select Angle, Centre, Point.
  2. The Arc angle dialog will be displayed. Type in the angle of the arc.
  3. A positive number draws an arc anticlockwise; a negative number will draw in a clockwise direction. Click OK.
  4. Click the position for the centre of the arc (point 1 in the diagram below). Now you will see an arc of the specified length rotating around this centre point as you move the cursor.
  5. Click the point at which the arc starts (point 2 in the diagram below). This fixes the location and radius of the arc.

This diagram shows four arcs, each with the same angle (90 degrees) and centre:

Angle, Point, Point constructs an arc through a given angle by placing its start and end points on the circumference.

  1. Select Angle, Point, Point.
  2. The Arc angle dialog will be displayed:

    Type in the angle of the arc. A positive number will draw an arc anticlockwise; a negative number will draw in a clockwise direction. Click OK.
  1. Click the position for the start of the arc (point 1 in the diagram).
  2. Click the position for the end of the arc (point 2 in the diagram).



Centre, Point, Point constructs a linestring from a circular arc of maximum 180 degrees with a known centre point, start point and end point.

  1. Select Centre, Point, Point.
  2. Click a point for the centre of the arc.
  3. Click a point for the end of the arc (point 2 in the diagram below). The arc is drawn using the shortest route between both points and has a maximum angle of 180 degrees.
    The position of the end point relative to the start therefore governs whether the arc is drawn clockwise or anti-clockwise:

Radius, Centre, Point, Point constructs a LineString item from an arc in a similar way to Centre, Point, Point, except that you are required to enter a specific radius before giving the centre, then two points on the circumference.

  1. Select Radius, Centre, Point, Point.
  2. The Radius of arc dialog will be displayed:

  3. Type in the radius of the arc and click OK.
  4. Click a position on screen where the arc will start.
  5. Click a position near the end of the arc. The end position is in fact determined by the radius you have entered; this point is used to indicate the direction in which the end point lies from the first point.