More accurate solution for planet diameter

Author: gzotti

src/core/modules/Planet.cpp

@@ -2567,7 +2567,7 @@ float Planet::getVMagnitude(const StelCore* core) const
 double Planet::getAngularSize(const StelCore* core) const
 {
 	const double rad = (rings ? rings->getSize() : equatorialRadius);
-	return std::atan2(rad*sphereScale,getJ2000EquatorialPos(core).length()) * M_180_PI;
+	return std::asin(rad*sphereScale/getJ2000EquatorialPos(core).length()) * M_180_PI;
 }
 
 

src/core/modules/StarMgr.cpp

@@ -1278,7 +1278,7 @@ void StarMgr::draw(StelCore* core)
 	PlanetP moon = GETSTELMODULE(SolarSystem)->getMoon();
 	Vec3d moonPos=moon->getJ2000EquatorialPos(core);
 	const double moonRadius = moon->getEquatorialRadius() * moon->getSphereScale();
-	double angularSize = atan2(moonRadius, moonPos.length());
+	double angularSize = asin(moonRadius / moonPos.length());
 	moonPos.normalize();
 	SphericalCap moonCap(moonPos, cos(angularSize));
 	for (auto  cap : viewportCaps)