Extinction Class Reference

#include <RefractionExtinction.hpp>

Public Types
enum	UndergroundExtinctionMode { UndergroundExtinctionZero = 0, UndergroundExtinctionMax = 1, UndergroundExtinctionMirror = 2 }
	Define the extinction strategy for rendering underground objects (useful when ground is not rendered) More...

Public Member Functions
void	forward (const Vec3d &altAzPos, float *mag) const
	Compute extinction effect for given position vector and magnitude. More...
void	forward (const Vec3f &altAzPos, float *mag) const
void	backward (const Vec3d &altAzPos, float *mag) const
	Compute inverse extinction effect for given position vector and magnitude. More...
void	backward (const Vec3f &altAzPos, float *mag) const
void	setExtinctionCoefficient (float k)
	Set visual extinction coefficient (mag/airmass), influences extinction computation. More...
float	getExtinctionCoefficient () const
void	setUndergroundExtinctionMode (UndergroundExtinctionMode mode)
UndergroundExtinctionMode	getUndergroundExtinctionMode () const
float	airmass (float cosZ, const bool apparent_z=true) const
	airmass computation for More...

Detailed Description

This class performs extinction computations, following literature from atmospheric optics and astronomy. Airmass computations are limited to meaningful altitudes. The solution provided here will [hopefully!] result in a visible "zone of avoidance" near the horizon down to altitude -2, and may show stars in their full brightness below -2 degrees. Typical horizons do not go down below -1, so all natural sites should be covered. Note that forward/backward are no absolute reverse operations! All the computations should be in effect (1) only if atmosphere effects are true (2) only for terrestrial locations, not on Moon/Mars/Saturn etc config.ini:astro/flag_extinction_below_horizon=true|false controls if extinction kills objects below -2 degrees altitude by setting airmass to 42.

Member Enumeration Documentation

UndergroundExtinctionMode

enum Extinction::UndergroundExtinctionMode

Enumerator
UndergroundExtinctionZero	Zero extinction: stars visible in full brightness.
UndergroundExtinctionMax	Maximum extinction: coef 42, i.e practically invisible.
UndergroundExtinctionMirror	Mirror the extinction for the same altutide above the ground.

Member Function Documentation

airmass()

float Extinction::airmass	(	float	cosZ,
		const bool	apparent_z = true
	)		const

Parameters

cosZ	= cosine of zenith angle z (=sin(altitude)!). The default (
apparent_z	= true) is computing airmass from observed altitude, following Rozenberg (1966) [X(90)~40]. if (
apparent_z	= false), we have geometrical altitude and compute airmass from that, following Young: Air mass and refraction. Applied Optics 33(6), pp.1108-1110, 1994. [X(90)~32]. A problem is that refraction depends on air pressure and temperature, but Young's formula assumes T=15C, p=1013.25mbar. So, it seems better to compute refraction first, and then use the Rozenberg formula here. Rozenberg is infinite at Z=92.17 deg, Young at Z=93.6 deg, so this function RETURNS SUBHORIZONTAL_AIRMASS BELOW -2 DEGREES!

backward()

void Extinction::backward ( const Vec3d &  altAzPos, float *  mag  ) const

inline

Parameters

altAzPos

is the NORMALIZED (!!) (geometrical) star position vector, and its z component is therefore sin(geometric_altitude). This call must therefore be done after application of Refraction effects if atmospheric effects are on. Note that forward/backward are no absolute reverse operations!

forward()

void Extinction::forward ( const Vec3d &  altAzPos, float *  mag  ) const

inline

Parameters

altAzPos

is the NORMALIZED (!!) (geometrical) star position vectors, and its z component is therefore sin(geometric_altitude). This call must therefore be done before application of Refraction if atmospheric effects are on. Note that forward/backward are no absolute reverse operations!

setExtinctionCoefficient()

void Extinction::setExtinctionCoefficient ( float  k )

inline

Parameters

k=	0.1 for highest mountains, 0.2 for very good lowland locations, 0.35 for typical lowland, 0.5 in humid climates.