lsst::ap::Point Struct Reference

A point on the unit sphere (sky), specified in spherical polar coordinates. More...

#include <Point.h>

Public Member Functions
	Point ()
	Point (double const ra, double const dec)
Point &	perturb (lsst::afw::math::Random &rng, double const sigma)
Point &	perturb (lsst::afw::math::Random &rng, double const sigma, double pa)
double	distance (Point const &p) const

Static Public Member Functions
static Point const	random (lsst::afw::math::Random &rng)
static Point const	random (lsst::afw::math::Random &rng, double const decMin, double const decMax)
static Point const	random (lsst::afw::math::Random &rng, double const raMin, double const raMax, double const decMin, double const decMax)

Public Attributes
double	_ra
double	_dec

Detailed Description

A point on the unit sphere (sky), specified in spherical polar coordinates.

The units of all angles (stored or passed to member functions) are degrees.

Definition at line 46 of file Point.h.

Constructor & Destructor Documentation

lsst::ap::Point::Point ( )

inline

Definition at line 51 of file Point.h.

: _ra(0.0), _dec(0.0) {}

lsst::ap::Point::Point ( double const  ra, double const  dec  )

inline

Definition at line 52 of file Point.h.

: _ra(ra), _dec(dec) {}

Member Function Documentation

double lsst::ap::Point::distance

(

Point const &

p

)

const

Returns the angular distance to the given point (in degrees).

Definition at line 138 of file Point.cc.

                                                  {

    double sra  = std::sin(afwGeom::degToRad(_ra));
    double cra  = std::cos(afwGeom::degToRad(_ra));
    double sdec = std::sin(afwGeom::degToRad(_dec));
    double cdec = std::cos(afwGeom::degToRad(_dec));

    double x = cra*cdec;
    double y = sra*cdec;
    double z = sdec;

    sra  = std::sin(afwGeom::degToRad(p._ra));
    cra  = std::cos(afwGeom::degToRad(p._ra));
    sdec = std::sin(afwGeom::degToRad(p._dec));
    cdec = std::cos(afwGeom::degToRad(p._dec));

    x *= cra*cdec;
    y *= sra*cdec;
    z *= sdec;

    return afwGeom::radToDeg(std::acos(x + y + z));
}

lsst::ap::Point & lsst::ap::Point::perturb	(	lsst::afw::math::Random &	rng,
		double const	sigma
	)

Randomly perturbs the point such that the results are distributed according to a normal distribution centered on the original point and having a standard deviation of sigma degrees.

Definition at line 73 of file Point.cc.

                                                                   {
    return perturb(rng, sigma, rng.uniform()*360.0);
}

lsst::ap::Point & lsst::ap::Point::perturb	(	lsst::afw::math::Random &	rng,
		double const	sigma,
		double	pa
	)

Randomly perturbs the point in the direction given by the specified position angle so that the distance to the original point is normally distributed with a standard deviation of sigma degrees.

Definition at line 82 of file Point.cc.

                                                                                    {

    double sra  = std::sin(afwGeom::degToRad(_ra));
    double cra  = std::cos(afwGeom::degToRad(_ra));
    double sdec = std::sin(afwGeom::degToRad(_dec));
    double cdec = std::cos(afwGeom::degToRad(_dec));

    // original position p
    double x = cra*cdec;
    double y = sra*cdec;
    double z = sdec;

    double spa = std::sin(afwGeom::degToRad(pa));
    double cpa = std::cos(afwGeom::degToRad(pa));

    // north vector tangential to p
    double nx = - cra*sdec;
    double ny = - sra*sdec;
    double nz =   cdec;

    // east vector tangential to p
    double ex = - sra;
    double ey =   cra;
    double ez =   0.0;

    // rotate north vector at V by minus position angle
    double tx = spa*ex + cpa*nx;
    double ty = spa*ey + cpa*ny;
    double tz = spa*ez + cpa*nz;

    // perturb in this direction by a random angle that is normally
    // distributed with a standard deviation of sigma degrees
    double mag  = afwGeom::degToRad(rng.gaussian()*sigma);
    double smag = std::sin(mag);
    double cmag = std::cos(mag);

    // obtain the perturbed position
    x = x*cmag + tx*smag;
    y = y*cmag + ty*smag;
    z = z*cmag + tz*smag;
    // finally, convert back to spherical coordinates (in degrees)
    _ra = afwGeom::radToDeg(std::atan2(y, x));
    if (_ra < 0.0) {
        _ra += 360.0;
    }
    _dec = afwGeom::radToDeg(std::asin(z));
    if (_dec <= -90.0) {
        _dec = -90.0;
    } else if (_dec >= 90.0) {
        _dec = 90.0;
    }
    return *this;
}

lsst::ap::Point const lsst::ap::Point::random ( lsst::afw::math::Random &  rng )

static

Picks a point uniformly at random on the unit sphere.

Definition at line 163 of file Point.cc.

                                                  {
    double z = rng.flat(-1.0, 1.0);
    return Point(rng.flat(0.0, 360.0), afwGeom::radToDeg(std::asin(z)));
}

lsst::ap::Point const lsst::ap::Point::random ( lsst::afw::math::Random &  rng, double const  decMin, double const  decMax  )

static

Picks a point uniformly at random in the specified dec band.

Definition at line 170 of file Point.cc.

  {
    return Point(rng.flat(0.0, 360.0), randomDec(rng, decMin, decMax));
}

lsst::ap::Point const lsst::ap::Point::random ( lsst::afw::math::Random &  rng, double const  raMin, double const  raMax, double const  decMin, double const  decMax  )

static

Picks a point uniformly at random in the specified box.

Definition at line 180 of file Point.cc.

  {
    assert(raMin >= 0.0 && raMin <= 360.0);
    assert(raMax >= 0.0 && raMax <= 360.0);

    double ra;
    if (raMin < raMax) {
        ra = rng.flat(raMin, raMin);
        if (ra > raMax) {
            ra = raMax;
        }
    } else {
        // wrap-around
        double m = raMin - 360.0;
        ra = rng.flat(m, raMax);
        if (ra < 0) {
            ra += 360.0;
        }
    }
    return Point(ra, randomDec(rng, decMin, decMax));
}

Member Data Documentation

double lsst::ap::Point::_dec

Definition at line 49 of file Point.h.

double lsst::ap::Point::_ra

Definition at line 48 of file Point.h.

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

• /lsst/home/lsstsw/stack/Linux64/ap/master-g60f1e072bb+1/include/lsst/ap/Point.h
• /lsst/home/lsstsw/stack/Linux64/ap/master-g60f1e072bb+1/src/Point.cc