lsst::gauss2d::Covariance Class Reference

A representation of a 2D Gaussian with x and y standard deviations and a covariance value. More...

#include <ellipse.h>

Inheritance diagram for lsst::gauss2d::Covariance:

Public Member Functions
	Covariance (double sigma_x_sq=0, double sigma_y_sq=0, double cov_xy=0)
	Construct a new Covariance object.
	Covariance (const Ellipse &ell)
	Construct a covariance using values from an ellipse instance.
void	convolve (const Covariance &cov)
	Convolve with another covariance, adding the values of each parameter to this.
double	get_sigma_x_sq () const
	Get the square of sigma_x.
double	get_sigma_y_sq () const
	Get the square of sigma_y.
double	get_cov_xy () const
	Get the covariance.
std::array< double, 3 >	get_xyc () const
	Get the array of sigma_x^2, sigma_y^2, covariance.
std::shared_ptr< Covariance >	make_convolution (const Covariance &cov) const
	Return the convolution of this with another covariance.
std::unique_ptr< Covariance >	make_convolution_uniq (const Covariance &cov) const
	Same as make_convolution(), but returning a unique_ptr.
void	set (const Ellipse &ellipse)
	Set values from an ellipse instance.
void	set (double sigma_x_sq=0, double sigma_y_sq=0, double cov_xy=0)
	Set all values at once.
void	set_sigma_x_sq (double sigma_x_sq)
	Set the square of sigma_x.
void	set_sigma_y_sq (double sigma_y_sq)
	Set the square of sigma_y.
void	set_cov_xy (double cov_xy)
	Set the off-diagonal (covariance) term.
void	set_xyc (const std::array< double, 3 > &xyc)
	Set sigma_x_sq, sigma_y_sq and cov_xy from an array ref.
std::string	repr (bool name_keywords=false, std::string_view namespace_separator=Object::CC_NAMESPACE_SEPARATOR) const override
	Return a full, callable string representation of this.
std::string	str () const override
	Return a brief, human-readable string representation of this.
bool	operator== (const Covariance &other) const
bool	operator!= (const Covariance &other) const

Static Public Member Functions
static void	check (double sigma_x_sq, double sigma_y_sq, double cov_xy)
	Check whether the supplied values are valid, throwing if not.
static std::string_view	null_str (const std::string_view &namespace_separator)

Static Public Attributes
static constexpr std::string_view	CC_NAMESPACE_SEPARATOR = "::"
	The C++ namespace separator.
static constexpr std::string_view	NULL_STR_GENERAL = "None"
static constexpr std::string_view	PY_NAMESPACE_SEPARATOR = "."

Friends
std::ostream &	operator<< (std::ostream &out, const Covariance &obj)

Detailed Description

A representation of a 2D Gaussian with x and y standard deviations and a covariance value.

This ellipse representation is intended for intermediate calculations and does not use an abstract Data class.

Note

The covariance is equal to sigma_x*sigma_y*rho, where -1 < rho < 1. Covariance values implying rho values outside this range are invalid.

Definition at line 57 of file ellipse.h.

Constructor & Destructor Documentation

Covariance() [1/2]

lsst::gauss2d::Covariance::Covariance ( double sigma_x_sq = 0, double sigma_y_sq = 0, double cov_xy = 0 )

explicit

Construct a new Covariance object.

Parameters

sigma_x_sq	The value of sigma_x^2
sigma_y_sq	The value of sigma_y^2
cov_xy	The value of the covariance

Definition at line 40 of file ellipse.cc.

                                                                          {
    set(sigma_x_sq, sigma_y_sq, cov_xy);
}

Covariance() [2/2]

lsst::gauss2d::Covariance::Covariance ( const Ellipse & ell )

explicit

Construct a covariance using values from an ellipse instance.

Definition at line 44 of file ellipse.cc.

{ set(ell); }

Member Function Documentation

check()

void lsst::gauss2d::Covariance::check ( double sigma_x_sq, double sigma_y_sq, double cov_xy )

static

Check whether the supplied values are valid, throwing if not.

Definition at line 46 of file ellipse.cc.

                                                                          {
    double offdiag_max = sqrt(sigma_x_sq) * sqrt(sigma_y_sq);
    // Define implied rho as -1 for negative cov and +1 for positive cov if zero size
    // This enforces cov_xy == 0 if sigma_x_sq == sigma_y_sq == 0
    double rho = offdiag_max > 0 ? cov_xy / offdiag_max : (cov_xy > 0) - (cov_xy < 0);
    if (!(sigma_x_sq >= 0) || !(sigma_y_sq >= 0) || !(rho >= -1 && rho <= 1)) {
        throw std::invalid_argument("Invalid sigma_x_sq, sigma_y_sq, cov_xy=" + to_string_float(sigma_x_sq)
                                    + "," + to_string_float(sigma_y_sq) + "," + to_string_float(cov_xy)
                                    + " with implied rho=" + to_string_float(rho)
                                    + "; sigma_x,y_sq >= 0 and -1 < rho < 1 required.");
    }
}

convolve()

void lsst::gauss2d::Covariance::convolve

(

const Covariance &

cov

)

Convolve with another covariance, adding the values of each parameter to this.

Definition at line 59 of file ellipse.cc.

                                               {
    double sigma_x_sq = this->get_sigma_x_sq() + cov.get_sigma_x_sq();
    double sigma_y_sq = this->get_sigma_y_sq() + cov.get_sigma_y_sq();
    double cov_xy = this->get_cov_xy() + cov.get_cov_xy();
    this->set(sigma_x_sq, sigma_y_sq, cov_xy);
}

get_cov_xy()

double lsst::gauss2d::Covariance::get_cov_xy ( ) const

inline

Get the covariance.

Definition at line 79 of file ellipse.h.

{ return _cov_xy; };

get_sigma_x_sq()

double lsst::gauss2d::Covariance::get_sigma_x_sq ( ) const

inline

Get the square of sigma_x.

Definition at line 75 of file ellipse.h.

{ return _sigma_x_sq; };

get_sigma_y_sq()

double lsst::gauss2d::Covariance::get_sigma_y_sq ( ) const

inline

Get the square of sigma_y.

Definition at line 77 of file ellipse.h.

{ return _sigma_y_sq; };

get_xyc()

std::array< double, 3 > lsst::gauss2d::Covariance::get_xyc ( ) const

inline

Get the array of sigma_x^2, sigma_y^2, covariance.

Definition at line 81 of file ellipse.h.

{ return {_sigma_x_sq, _sigma_y_sq, _cov_xy}; }

make_convolution()

std::shared_ptr< Covariance > lsst::gauss2d::Covariance::make_convolution

(

const Covariance &

cov

)

const

Return the convolution of this with another covariance.

Convolution simply sums the values of each respective parameter.

Parameters

cov	The covariance to convolve with.

Returns

A new covariance with values set to the convolution.

Definition at line 66 of file ellipse.cc.

                                                                                  {
    std::shared_ptr<Covariance> cov_ret = std::make_shared<Covariance>(
            this->get_sigma_x_sq(), this->get_sigma_y_sq(), this->get_cov_xy());
    cov_ret->convolve(cov);
    return cov_ret;
}

make_convolution_uniq()

std::unique_ptr< Covariance > lsst::gauss2d::Covariance::make_convolution_uniq

(

const Covariance &

cov

)

const

Same as make_convolution(), but returning a unique_ptr.

null_str()

static std::string_view lsst::gauss2d::Object::null_str ( const std::string_view & namespace_separator )

inlinestaticinherited

Definition at line 49 of file object.h.

                                                                              {
        return namespace_separator == CC_NAMESPACE_SEPARATOR ? "nullptr" : NULL_STR_GENERAL;
    }

operator!=()

bool lsst::gauss2d::Covariance::operator!=

(

const Covariance &

other

)

const

Definition at line 135 of file ellipse.cc.

{ return !(*this == other); }

operator==()

bool lsst::gauss2d::Covariance::operator==

(

const Covariance &

other

)

const

Definition at line 134 of file ellipse.cc.

{ return get_xyc() == other.get_xyc(); }

repr()

std::string lsst::gauss2d::Covariance::repr ( bool name_keywords = false, std::string_view namespace_separator = Object::CC_NAMESPACE_SEPARATOR ) const

overridevirtual

Return a full, callable string representation of this.

Parameters

name_keywords	Whether to prefix arguments with "{name}=", where name is the arg name in the header (as with keyword arguments in Python).
namespace_separator	The string to use to delimit namespaces, i.e. :: in C++ and . in Python.

Returns

A callable string representation of this, which should return an an identical object to this.

Note

The representation with name_keywords=false must be callable in C++. The representation with name_keywords=true should be callable in Python, if there are any bindings.

Implements lsst::gauss2d::Object.

Definition at line 122 of file ellipse.cc.

                                                                                       {
    return type_name_str<Covariance>(false, namespace_separator) + "(" + (name_keywords ? "sigma_x_sq=" : "")
           + to_string_float(_sigma_x_sq) + ", " + (name_keywords ? "sigma_y_sq=" : "")
           + to_string_float(_sigma_y_sq) + ", " + (name_keywords ? "cov_xy=" : "") + to_string_float(_cov_xy)
           + ")";
}

set() [1/2]

void lsst::gauss2d::Covariance::set

(

const Ellipse &

ellipse

)

Set values from an ellipse instance.

Definition at line 73 of file ellipse.cc.

                                           {
    double sigma_x = ellipse.get_sigma_x();
    double sigma_y = ellipse.get_sigma_y();
    double rho = ellipse.get_rho();
    this->_sigma_x_sq = sigma_x * sigma_x;
    this->_sigma_y_sq = sigma_y * sigma_y;
    // Must be done like so in case sigma_x/y^2 round to zero, and check after
    this->set_cov_xy(sigma_x * sigma_y * (_sigma_x_sq > 0) * (_sigma_y_sq > 0) * rho);
}

set() [2/2]

void lsst::gauss2d::Covariance::set	(	double	sigma_x_sq = 0,
		double	sigma_y_sq = 0,
		double	cov_xy = 0 )

Set all values at once.

Definition at line 83 of file ellipse.cc.

                                                                        {
    set_sigma_x_sq(sigma_x_sq);
    set_sigma_y_sq(sigma_y_sq);
    set_cov_xy(cov_xy);
}

set_cov_xy()

void lsst::gauss2d::Covariance::set_cov_xy

(

double

cov_xy

)

Set the off-diagonal (covariance) term.

Definition at line 105 of file ellipse.cc.

                                         {
    // Take individual sqrt just to be safe and avoid potential overflow
    double offdiag_max = sqrt(_sigma_x_sq) * sqrt(_sigma_y_sq);
    // If offdiag_max is zero, we can only accept cov_xy exactly zero
    double rho = offdiag_max > 0 ? cov_xy / offdiag_max : -!(cov_xy >= 0) + !(cov_xy <= 0);
    if (!(rho > -1 && rho < 1)) {
        throw std::invalid_argument(this->str() + "can't set invalid cov_xy=" + to_string_float(cov_xy)
                                    + " (>0=" + to_string_float(cov_xy > 0)
                                    + ", <0=" + to_string_float(cov_xy < 0)
                                    + ", offdiag_max=" + to_string_float(offdiag_max) + " with implied rho="
                                    + to_string_float(rho) + "; -1 < rho < 1 required.");
    }
    _cov_xy = cov_xy;
}

set_sigma_x_sq()

void lsst::gauss2d::Covariance::set_sigma_x_sq

(

double

sigma_x_sq

)

Set the square of sigma_x.

Definition at line 89 of file ellipse.cc.

                                                 {
    if (!(sigma_x_sq >= 0)) {
        throw std::invalid_argument(this->str() + " can't set invalid sigma_x_sq="
                                    + to_string_float(sigma_x_sq) + "; sigma_x_sq >= 0 required.");
    }
    _sigma_x_sq = sigma_x_sq;
}

set_sigma_y_sq()

void lsst::gauss2d::Covariance::set_sigma_y_sq

(

double

sigma_y_sq

)

Set the square of sigma_y.

Definition at line 97 of file ellipse.cc.

                                                 {
    if (!(sigma_y_sq >= 0)) {
        throw std::invalid_argument(this->str() + " can't set invalid sigma_y_sq="
                                    + to_string_float(sigma_y_sq) + "; sigma_y_sq >= 0 required.");
    }
    _sigma_y_sq = sigma_y_sq;
}

set_xyc()

void lsst::gauss2d::Covariance::set_xyc

(

const std::array< double, 3 > &

xyc

)

Set sigma_x_sq, sigma_y_sq and cov_xy from an array ref.

Definition at line 120 of file ellipse.cc.

{ this->set(xyc[0], xyc[1], xyc[2]); }

str()

std::string lsst::gauss2d::Covariance::str ( ) const

overridevirtual

Return a brief, human-readable string representation of this.

Implements lsst::gauss2d::Object.

Definition at line 129 of file ellipse.cc.

                                {
    return type_name_str<Covariance>(true) + "(sigma_x_sq=" + to_string_float(_sigma_x_sq)
           + ", sigma_y_sq=" + to_string_float(_sigma_y_sq) + ", cov_xy=" + to_string_float(_cov_xy) + ")";
}

Friends And Related Symbol Documentation

operator<<

std::ostream & operator<< ( std::ostream & out, const Covariance & obj )

friend

Definition at line 137 of file ellipse.cc.

                                                               {
    out << obj.str();
    return out;
}

Member Data Documentation

CC_NAMESPACE_SEPARATOR

std::string_view lsst::gauss2d::Object::CC_NAMESPACE_SEPARATOR = "::"

staticconstexprinherited

The C++ namespace separator.

Definition at line 45 of file object.h.

NULL_STR_GENERAL

std::string_view lsst::gauss2d::Object::NULL_STR_GENERAL = "None"

staticconstexprinherited

Definition at line 46 of file object.h.

PY_NAMESPACE_SEPARATOR

std::string_view lsst::gauss2d::Object::PY_NAMESPACE_SEPARATOR = "."

staticconstexprinherited

Definition at line 47 of file object.h.

---

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

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-10.1.0/Linux/gauss2d/g9125e01d80+fcb1d3bbc8/include/lsst/gauss2d/ellipse.h
• /j/snowflake/release/lsstsw/stack/lsst-scipipe-10.1.0/Linux/gauss2d/g9125e01d80+fcb1d3bbc8/src/ellipse.cc