The SKIRT project
advanced radiative transfer for astrophysics
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SphericalBackgroundSource Class Reference

#include <SphericalBackgroundSource.hpp>

Inheritance diagram for SphericalBackgroundSource:
Inheritance graph
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Public Member Functions

double backgroundRadius () const
 
int intrinsicDimension () const override
 
void launchSpecialty (PhotonPacket *pp, size_t historyIndex, double lambda, double Lw, VelocityInterface *bvi) const override
 
- Public Member Functions inherited from CenteredSource
double centerX () const
 
double centerY () const
 
double centerZ () const
 
int geometryDimension () const override
 
virtual int intrinsicDimension () const =0
 
- Public Member Functions inherited from SpecialtySource
int dimension () const override
 
virtual int geometryDimension () const =0
 
bool hasVelocity () const override
 
void launchNormalized (PhotonPacket *pp, size_t historyIndex, double lambda, double Lw) const override
 
virtual void launchSpecialty (PhotonPacket *pp, size_t historyIndex, double lambda, double Lw, VelocityInterface *bvi) const =0
 
Vec velocity () const override
 
double velocityX () const
 
double velocityY () const
 
double velocityZ () const
 
- Public Member Functions inherited from NormalizedSource
void launch (PhotonPacket *pp, size_t historyIndex, double L) const override
 
virtual void launchNormalized (PhotonPacket *pp, size_t historyIndex, double lambda, double Lw) const =0
 
double luminosity () const override
 
LuminosityNormalizationnormalization () const
 
SEDsed () const
 
double specificLuminosity (double wavelength) const override
 
Range wavelengthRange () const override
 
- Public Member Functions inherited from Source
virtual int dimension () const =0
 
virtual bool hasVelocity () const =0
 
virtual void launch (PhotonPacket *pp, size_t historyIndex, double L) const =0
 
virtual double luminosity () const =0
 
virtual void prepareForLaunch (double sourceBias, size_t firstIndex, size_t numIndices)
 
double sourceWeight () const
 
virtual double specificLuminosity (double wavelength) const =0
 
double wavelengthBias () const
 
WavelengthDistributionwavelengthBiasDistribution () const
 
- Public Member Functions inherited from SimulationItem
template<class T >
T * find (bool setup=true) const
 
template<class T >
T * interface (int levels=-999999, bool setup=true) const
 
virtual string itemName () const
 
void setup ()
 
string typeAndName () const
 
- Public Member Functions inherited from Item
 Item (const Item &)=delete
 
virtual ~Item ()
 
void addChild (Item *child)
 
const vector< Item * > & children () const
 
virtual void clearItemListProperty (const PropertyDef *property)
 
void destroyChild (Item *child)
 
virtual bool getBoolProperty (const PropertyDef *property) const
 
virtual vector< double > getDoubleListProperty (const PropertyDef *property) const
 
virtual double getDoubleProperty (const PropertyDef *property) const
 
virtual string getEnumProperty (const PropertyDef *property) const
 
virtual int getIntProperty (const PropertyDef *property) const
 
virtual vector< Item * > getItemListProperty (const PropertyDef *property) const
 
virtual ItemgetItemProperty (const PropertyDef *property) const
 
virtual string getStringProperty (const PropertyDef *property) const
 
int getUtilityProperty (string name) const
 
virtual void insertIntoItemListProperty (const PropertyDef *property, int index, Item *item)
 
Itemoperator= (const Item &)=delete
 
Itemparent () const
 
virtual void removeFromItemListProperty (const PropertyDef *property, int index)
 
virtual void setBoolProperty (const PropertyDef *property, bool value)
 
virtual void setDoubleListProperty (const PropertyDef *property, vector< double > value)
 
virtual void setDoubleProperty (const PropertyDef *property, double value)
 
virtual void setEnumProperty (const PropertyDef *property, string value)
 
virtual void setIntProperty (const PropertyDef *property, int value)
 
virtual void setItemProperty (const PropertyDef *property, Item *item)
 
virtual void setStringProperty (const PropertyDef *property, string value)
 
void setUtilityProperty (string name, int value)
 
virtual string type () const
 
- Public Member Functions inherited from WavelengthRangeInterface
virtual ~WavelengthRangeInterface ()
 
virtual Range wavelengthRange () const =0
 
- Public Member Functions inherited from VelocityInterface
virtual ~VelocityInterface ()
 
virtual Vec velocity () const =0
 

Protected Member Functions

 SphericalBackgroundSource ()
 
- Protected Member Functions inherited from CenteredSource
 CenteredSource ()
 
- Protected Member Functions inherited from SpecialtySource
 SpecialtySource ()
 
void setupSelfBefore () override
 
- Protected Member Functions inherited from NormalizedSource
 NormalizedSource ()
 
void setupSelfAfter () override
 
void setupSelfBefore () override
 
- Protected Member Functions inherited from Source
 Source ()
 
void informAvailableWavelengthRange (Range available, string itemType)
 
Randomrandom () const
 
void setupSelfBefore () override
 
- Protected Member Functions inherited from SimulationItem
 SimulationItem ()
 
virtual bool offersInterface (const std::type_info &interfaceTypeInfo) const
 
virtual void setupSelfAfter ()
 
virtual void setupSelfBefore ()
 
- Protected Member Functions inherited from Item
 Item ()
 
- Protected Member Functions inherited from SourceWavelengthRangeInterface
 SourceWavelengthRangeInterface ()
 
- Protected Member Functions inherited from WavelengthRangeInterface
 WavelengthRangeInterface ()
 
- Protected Member Functions inherited from VelocityInterface
 VelocityInterface ()
 

Private Types

using BaseType = CenteredSource
 
using ItemType = SphericalBackgroundSource
 

Private Attributes

double _backgroundRadius
 

Friends

class ItemRegistry
 

Detailed Description

The SphericalBackgroundSource class represents the surface of a sphere of radius \(r_{\text{bg}}\) from which radiation escapes in the inward direction. The emissivity of this source is anisotropic. There is no radiation outwards and the intensity is proportional to \(\cos\theta'\) in the inward hemisphere, where \(\theta'\) is the angle between the direction and the normal on the surface.

Constructor & Destructor Documentation

◆ SphericalBackgroundSource()

SphericalBackgroundSource::SphericalBackgroundSource ( )
inlineprotected

Default constructor for concrete Item subclass SphericalBackgroundSource : "a spherical background source with an anisotropic inward radiation field" .

Member Function Documentation

◆ backgroundRadius()

SphericalBackgroundSource::backgroundRadius ( ) const
inline

This function returns the value of the discoverable double property backgroundRadius : "the radius of the background sphere" .

This property represents a physical quantity of type "length" .

The minimum value for this property is "]0" .

◆ intrinsicDimension()

int SphericalBackgroundSource::intrinsicDimension ( ) const
overridevirtual

This function returns the intrinsic dimension of the geometry, which is 1 in this case: the geometry is spherically symmetric, even with the anisotropic emissivity.

Implements CenteredSource.

◆ launchSpecialty()

void SphericalBackgroundSource::launchSpecialty ( PhotonPacket pp,
size_t  historyIndex,
double  lambda,
double  Lw,
VelocityInterface bvi 
) const
overridevirtual

This function causes the photon packet pp to be launched from the source using the given history index, wavelength, weighted luminosity contribution, and redshift interface (corresponding to the bulk velocity of the source).

Firstly, the function generates a random inward launch position \({\bf{r}}\) on the background surface by drawing a random direction \({\bf{u}}\) on the unit sphere and transforming it to take into account the background radius and center position. The direction \({\bf{u}}\) actually corresponds to the outward normal to the background surface at the position \({\bf{r}}\).

Secondly, the function generates a random direction \({\bf{k}}\) appropriate for the anisotropic inward radiation field at the location \({\bf{r}}\), or equivalently, for the normal \({\bf{u}}\). In a spherical coordinate system with the Z' axis normal to the surface at the position \({\bf{r}}\), the probability distribution is given by

\[ p(\theta',\varphi')\, {\text{d}}\theta'\, {\text{d}}\varphi' = -\frac{1}{\pi}\cos\theta' \sin\theta'\,{\text{d}}\theta'\, {\text{d}}\varphi' \qquad \frac{\pi}{2} \leq \theta' < \pi. \]

Random angles \(\theta'\) and \(\varphi'\) can be determined by taking two uniform deviates \({\cal{X}}_1\) and \({\cal{X}}_2\) and solving the two equations

\[ \begin{split} {\cal{X}}_1 &= -\int_{\pi/2}^{\theta'} 2\sin\theta^{\prime\prime}\cos\theta^{\prime\prime}\,{\text{d}}\theta^{\prime\prime} \\ {\cal{X}}_2 &= \int_0^{\varphi'} \frac{{\text{d}}\varphi^{\prime\prime}}{2\pi} \end{split} \]

for \(\theta'\) and \(\varphi'\). The solution is readily found,

\[ \begin{split} \theta' &= \pi - \arccos \sqrt{{\cal{X}}_1} \\ \varphi' &= 2\pi\,{\cal{X}}_2. \end{split} \]

Once these values have been determined, we need to determine the coordinates of the vector \({\bf{k}}\) in the standard coordinate system. The link between the standard XYZ coordinate system and the one with the Z' axis determined by the normal \({\bf{u}}\) is a joint rotation over an angle \(\varphi\) along the Z-axis, followed by a rotation over an angle \(\theta\) over the Y'-axis, where \(\theta\) and \(\varphi\) are the polar angle and azimuth of the position vector \({\bf{r}}\). The connection is hence

\[ \begin{bmatrix} k'_x \\ k'_y \\ k'_z \end{bmatrix} = \begin{bmatrix} \cos\theta & 0 & -\sin\theta \\ 0 & 1 & 0 \\ \sin\theta & 0 & \cos\theta \end{bmatrix} \begin{bmatrix} \cos\phi & \sin\phi & 0 \\ -\sin\phi & \cos\phi & 0 \\ 0 & 0 & 1 \end{bmatrix} \begin{bmatrix} k_x \\ k_y \\ k_z \end{bmatrix} \]

or in the other direction

\[ \begin{bmatrix} k_x \\ k_y \\ k_z \end{bmatrix} = \begin{bmatrix} \cos\phi & -\sin\phi & 0 \\ \sin\phi & \cos\phi & 0 \\ 0 & 0 & 1 \end{bmatrix} \begin{bmatrix} \cos\theta & 0 & \sin\theta \\ 0 & 1 & 0 \\ -\sin\theta & 0 & \cos\theta \end{bmatrix} \begin{bmatrix} k'_x \\ k'_y \\ k'_z \end{bmatrix} \]

Thirdly, the function sets up a thread-local object that serves the angular distribution interface for a particular launch position. Configured with the appropriate launch position \({\bf{u}}\), this object is handed to the photon packet being launched so that peel-off photon packets can retrieve the appropriate bias factor for the instrument direction. This works even if there are multiple sources of this type because each thread handles a single photon packet at a time.

The local angular distribution object implements a function that returns the normalized probability for a direction \({\bf{k}}\), given that the point of emission is defined by the normal \({\bf{u}}\). The appropriate probability distribution is given by

\[ p({\bf{k}})\, {\text{d}}\Omega = \begin{cases} 0 & 0 \leq \theta' < \frac{\pi}{2} \\ -4\cos\theta'\, {\text{d}}\Omega & \frac{\pi}{2} \leq \theta' < \pi \end{cases} \]

Here \(\theta'\) is the angle between the direction \({\bf{k}}\) and the outward normal \({\bf{u}}\) on the stellar surface, i.e.

\[ \cos\theta' = {\bf{k} \cdot \bf{r}}. \]

This distribution is correctly normalized in the sense that

\[ \frac{1}{4\pi} \iint p({\bf{k}})\, {\text{d}}\Omega = 1. \]

Finally, the function launches the photon packet, passing it all of the above information.

Implements SpecialtySource.


The documentation for this class was generated from the following file: