What is the process for creating a circle using osgEarth::CircleNode?

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Here is an example code snippet for creating a circle using osgEarth::CircleNode:

#include <osgEarth/CircleNode>
#include <osgEarth/GeoData>

// create a GeoPoint as the center of the circle
osgEarth::GeoPoint center(osgEarth::SpatialReference::get("wgs84"), -105.2207, 40.0239, 0.0, osgEarth::ALTMODE_ABSOLUTE);

// create a CircleNode with a radius of 500 meters, 360 segments, and a red fill color
osgEarth::CircleNode* circle = new osgEarth::CircleNode(center, 500.0, 360, osgEarth::Color::Red);

// add the circle to a parent node or scene graph
parent->addChild(circle);

First, you need to create a GeoPoint to define the center of the circle. The GeoPoint includes a spatial reference (such as "wgs84"), latitude and longitude in degrees, and an altitude in meters (use 0.0 for 2D circles).

Next, create a CircleNode with the GeoPoint center, radius in meters, number of segments (for the circle's shape), and a fill color (optional).

Finally, add the CircleNode to a parent node or scene graph to visualize the circle.