Add sun and moon labels

[pjcozzi]

As mentioned in #1189

[pjcozzi]

No one has asked for this except me and this can be done at the app level so I am OK with closing this. Anyone feel otherwise?

[emackey]

Can we post a sample of app code that does this?

[mramato]

@emackey, here's a quick 2 minute example I whipped up using the Entity API. In 3D the near/far plane kicks in so you don't see them, but they do work in 2D.

var viewer = new Cesium.Viewer('cesiumContainer');

var sunPositionProperty = new Cesium.CallbackProperty(function(time, result){
    Cesium.Simon1994PlanetaryPositions.computeSunPositionInEarthInertialFrame(time, result);
     return Cesium.PositionProperty.convertToReferenceFrame(
        time,
        result,
        Cesium.ReferenceFrame.INERTIAL,
        Cesium.ReferenceFrame.FIXED,
        result);
}, false);

var moonPositionProperty = new Cesium.CallbackProperty(function(time, result){
    Cesium.Simon1994PlanetaryPositions.computeMoonPositionInEarthInertialFrame(time, result);
     return Cesium.PositionProperty.convertToReferenceFrame(
        time,
        result,
        Cesium.ReferenceFrame.INERTIAL,
        Cesium.ReferenceFrame.FIXED,
        result);
}, false);

viewer.entities.add({
    position :  sunPositionProperty,
    label : {
        text : 'Sun'
    }
});

viewer.entities.add({
    position :  moonPositionProperty,
    label : {
        text : 'Moon'
    }
});