MapCircle QML Type

The MapCircle type displays a geographic circle on a Map. More...

• List of all members, including inherited members

Properties

• border
  • border.width : int
  • border.color : color
• center : coordinate
• color : color
• opacity : real
• radius : real

Detailed Description

The MapCircle type displays a geographic circle on a Map, which consists of all points that are within a set distance from one central point. Depending on map projection, a geographic circle may not always be a perfect circle on the screen: for instance, in the Mercator projection, circles become ovoid in shape as they near the poles. To display a perfect screen circle around a point, use a MapQuickItem containing a relevant Qt Quick type instead.

By default, the circle is displayed as a 1 pixel black border with no fill. To change its appearance, use the color, border.color and border.width properties.

Internally, a MapCircle is implemented as a many-sided polygon. To calculate the radius points it uses a spherical model of the Earth, similar to the atDistanceAndAzimuth method of the coordinate type. These two things can occasionally have implications for the accuracy of the circle's shape, depending on position and map projection.

Note: Dragging a MapCircle (through the use of MouseArea) causes new points to be generated at the same distance (in meters) from the center. This is in contrast to other map items which store their dimensions in terms of latitude and longitude differences between vertices.

Performance

MapCircle performance is almost equivalent to that of a MapPolygon with 125 vertices. There is a small amount of additional overhead with respect to calculating the vertices first.

Like the other map objects, MapCircle is normally drawn without a smooth appearance. Setting the opacity property will force the object to be blended, which decreases performance considerably depending on the graphics hardware in use.

Example Usage

The following snippet shows a map containing a MapCircle, centered at the coordinate (-27, 153) with a radius of 5km. The circle is filled in green, with a 3 pixel black border.

Map {
    MapCircle {
        center {
            latitude: -27.5
            longitude: 153.0
        }
        radius: 5000.0
        color: 'green'
        border.width: 3
    }
}

Property Documentation