Index
Previous
Next

AspEdit manual      Adding / subtracting shapes

Purpose

It can be useful to be able to add shapes together or to subtract a shape from another shape.
Examples:
  • In a soaring contest the rules say some airspace areas can not be entered.  If these area are adjacent, you can transform them in a single contiguous area.
  • A glider airfield located in a CTR a has an exempted area in it. You can subtract the area from the CTR. This will show the CTR excluding the area.
  • In country A airways are embedded in controlled airspace, but in country B airspace is class G outside the airways. You'll need to define the airways in country B, but at the borders portions of the airways will also be drawn in country A. This will clutter the map.  The solution is to subtract country A from the airways.

General rules

  • Both Airspace areas and countries can be used.
  • Shapes must be closed.
  • In order to function in a logical way, all shapes should be rotating clockwise, see also below (adding or subtracting?).
  • Added / subtracted shapes must always be placed at the end of a shape.  All points / circles / borders after a shape will be ignored.
  • More than one shape can be added or subtracted.
  • You can add (subtract) a shape to an empty shape.  This will place an (inverted) copy of the shape in the area. After that you can add / subtract other shapes.

Adding / subtracting a shape

  • For all airspace areas except airways:
  1. In the Area dialog box, press the add or insert button.  Use the Insert button only to insert before another shape.
  2. The Add element dialog box will open.
  3. Select "Shape", the Add shape dialog box will open.
  4. Select the desired shape, specify add or subtract.
  • For airways:
  1. In the Area dialog box, press the add or insert button. Use Insert only to insert before another shape.
  2. The Add fix dialog box will open.
  3. Press the "Add shape" button.
  4. Select the desired shape, specify add or subtract.

Adding or subtracting?

In most geographical software, shapes are turning clockwise as standard. This means that when viewed from the center, the points of the shape are sequenced clockwise.  If both the source shape and the shape from which to insert a segment are clockwise, adding and subtracting will be in the logical way .
However, if one shape is counterclockwise, adding / subtracted will be inverted.
In any case, check the results on the map display.  If the result is not as expected, invert the selection.

Modifying an added / subtracted shape line

In the list of the Area dialog box, double-click on the line defining the shape operation, the Add shape dialog box will open for the selected segment

Exporting

Any area that contains an added / subtracted shape will be expanded.  This means that all circles will be defined by points, rather than the OpenAir DC / DB records.
The resolution of the circles will be as selected in the Map Settings dialog box.