Extinction Class Reference

This class performs extinction computations, following literature from atmospheric optics and astronomy. More...

#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

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.