Projector Class Reference

#include <projector.h>

Inheritance diagram for Projector:

Public Types
enum	Projection {   Lambert , AzimuthalEquidistant , Orthographic , Equirectangular ,   Stereographic , Gnomonic , UnknownProjection }

Public Member Functions
	Projector (const ViewParams &p)
bool	checkVisibility (const SkyPoint *p) const
QPointF	clipLine (SkyPoint *p1, SkyPoint *p2) const
Eigen::Vector2f	clipLineVec (SkyPoint *p1, SkyPoint *p2) const
virtual QPolygonF	clipPoly () const
double	findNorthPA (const SkyPoint *o, float x, float y) const
double	findPA (const SkyObject *o, float x, float y) const
double	findZenithPA (const SkyPoint *o, float x, float y) const
double	fov () const
virtual SkyPoint	fromScreen (const QPointF &p, dms *LST, const dms *lat, bool onlyAltAz=false) const
virtual QVector< Eigen::Vector2f >	groundPoly (SkyPoint *labelpoint=nullptr, bool *drawLabel=nullptr) const
bool	onScreen (const Eigen::Vector2f &p) const
bool	onScreen (const QPointF &p) const
void	setViewParams (const ViewParams &p)
QPointF	toScreen (const SkyPoint *o, bool oRefract=true, bool *onVisibleHemisphere=nullptr) const
virtual Eigen::Vector2f	toScreenVec (const SkyPoint *o, bool oRefract=true, bool *onVisibleHemisphere=nullptr) const
virtual Q_INVOKABLE Projection	type () const =0
virtual bool	unusablePoint (const QPointF &p) const
virtual void	updateClipPoly ()
ViewParams	viewParams () const

Protected Member Functions
virtual double	cosMaxFieldAngle () const
Eigen::Vector2f	derst (double x, double y) const
virtual double	projectionK (double x) const
virtual double	projectionL (double x) const
virtual double	radius () const
Eigen::Vector2f	rst (double x, double y) const

Static Protected Member Functions
static SkyPoint	pointAt (double az)

Protected Attributes
QPolygonF	m_clipPolygon
double	m_cosY0 { 0 }
KStarsData *	m_data { nullptr }
double	m_fov { 0 }
double	m_sinY0 { 0 }
ViewParams	m_vp

Detailed Description

The Projector class is the primary class that serves as an interface to handle projections.

Definition at line 57 of file projector.h.

Member Enumeration Documentation

Projection

enum Projector::Projection

Definition at line 77 of file projector.h.

Constructor & Destructor Documentation

Projector()

Projector::Projector ( const ViewParams & p )

explicit

Constructor.

Parameters

p	the ViewParams for this projection

Definition at line 38 of file projector.cpp.

Member Function Documentation

checkVisibility()

bool Projector::checkVisibility

(

const SkyPoint *

p

)

const

Determine if the skypoint p is likely to be visible in the display window.

checkVisibility() is an optimization function. It determines whether an object appears within the bounds of the skymap window, and therefore should be drawn. The idea is to save time by skipping objects which are off-screen, so it is absolutely essential that checkVisibility() is significantly faster than the computations required to draw the object to the screen.

If the ground is to be filled, the function first checks whether the point is below the horizon, because they will be covered by the ground anyways. Importantly, it does not call the expensive EquatorialToHorizontal function. This means that the horizontal coordinates MUST BE CORRECT! The vast majority of points are already synchronized, so recomputing the horizontal coordinates is a waste.

The function then checks the difference between the Declination/Altitude coordinate of the Focus position, and that of the point p. If the absolute value of this difference is larger than fov, then the function returns false. For most configurations of the sky map window, this simple check is enough to exclude a large number of objects.

Next, it determines if one of the poles of the current Coordinate System (Equatorial or Horizontal) is currently inside the sky map window. This is stored in the member variable 'bool SkyMap::isPoleVisible, and is set by the function SkyMap::setMapGeometry(), which is called by SkyMap::paintEvent(). If a Pole is visible, then it will return true immediately. The idea is that when a pole is on-screen it is computationally expensive to determine whether a particular position is on-screen or not: for many valid Dec/Alt values, all values of RA/Az will indeed be onscreen, but for other valid Dec/Alt values, only most RA/Az values are onscreen. It is cheaper to simply accept all "horizontal" RA/Az values, since we have already determined that they are on-screen in the "vertical" Dec/Alt coordinate.

Finally, if no Pole is onscreen, it checks the difference between the Focus position's RA/Az coordinate and that of the point p. If the absolute value of this difference is larger than XMax, the function returns false. Otherwise, it returns true.

Parameters

p	pointer to the skypoint to be checked.

Returns

true if the point p was found to be inside the Sky map window.

See also

SkyMap::setMapGeometry()

SkyMap::fov()

Note

If you are creating skypoints using equatorial coordinates, then YOU MUST CALL EQUATORIALTOHORIZONTAL BEFORE THIS FUNCTION!

To avoid calculating refraction, we just use the unrefracted altitude and add a 2-degree 'safety factor'

Definition at line 183 of file projector.cpp.

clipLine()

QPointF Projector::clipLine	(	SkyPoint *	p1,
		SkyPoint *	p2 ) const

ASSUMES *p1 did not clip but *p2 did.

Returns the QPointF on the line between *p1 and *p2 that just clips.

Definition at line 108 of file projector.cpp.

clipLineVec()

Eigen::Vector2f Projector::clipLineVec	(	SkyPoint *	p1,
		SkyPoint *	p2 ) const

ASSUMES *p1 did not clip but *p2 did.

Returns the Eigen::Vector2f on the line between *p1 and *p2 that just clips.

Definition at line 113 of file projector.cpp.

clipPoly()

QPolygonF Projector::clipPoly ( ) const

virtual

Returns

the clipping polygen covering the visible sky area. Anything outside this polygon is clipped by QPainter.

Definition at line 435 of file projector.cpp.

cosMaxFieldAngle()

virtual double Projector::cosMaxFieldAngle ( ) const

inlineprotectedvirtual

This function returns the cosine of the maximum field angle, i.e., the maximum angular distance from the focus for which a point should be projected.

Default is 0, i.e., 90 degrees.

Reimplemented in GnomonicProjector, and StereographicProjector.

Definition at line 299 of file projector.h.

derst()

Eigen::Vector2f Projector::derst ( double x, double y ) const

inlineprotected

Transform screen (x, y) to projector (x, y) accounting for scale, rotation.

Transforms the Cartesian position on the screen to the Cartesian position accepted by the projector algorithm by applying th escale factor, rotation and shift from SkyMap origin

rst stands for rotate-scale-translate

See also

rst

Definition at line 336 of file projector.h.

findNorthPA()

double Projector::findNorthPA	(	const SkyPoint *	o,
		float	x,
		float	y ) const

Determine the on-screen position angle of a SkyPont with recept with NCP.

This is the object's sky position angle (w.r.t. North). of "North" at the position of the object (w.r.t. the screen Y-axis). The latter is determined by constructing a test point with the same RA but a slightly increased Dec as the object, and calculating the angle w.r.t. the Y-axis of the line connecting the object to its test point.

Note

This method assumes that o->pa() returns a clockwise sense angle @fixme We seem to use different conventions across KStars

Definition at line 236 of file projector.cpp.

findPA()

double Projector::findPA	(	const SkyObject *	o,
		float	x,
		float	y ) const

Determine the on-screen position angle of a SkyObject.

This is the sum of the object's sky position angle (w.r.t. North), and the position angle of "North" at the position of the object (w.r.t. the screen Y-axis). The latter is determined by constructing a test point with the same RA but a slightly increased Dec as the object, and calculating the angle w.r.t. the Y-axis of the line connecting the object to its test point.

Definition at line 271 of file projector.cpp.

findZenithPA()

double Projector::findZenithPA	(	const SkyPoint *	o,
		float	x,
		float	y ) const

Determine the on-screen angle of a SkyPoint with respect to Zenith.

Note

Similar to

See also

findNorthPA

Note

It is assumed that EquatorialToHorizontal has been called on o

@description This is determined by constructing a test point with the same Azimuth but a slightly increased Altitude, and calculating the angle w.r.t. the Y-axis of the line connecting the object to its test point.

Definition at line 276 of file projector.cpp.

fov()

double Projector::fov

(

)

const

Return the FOV of this projection.

Definition at line 88 of file projector.cpp.

fromScreen()

SkyPoint Projector::fromScreen ( const QPointF & p, dms * LST, const dms * lat, bool onlyAltAz = false ) const

virtual

Determine RA, Dec coordinates of the pixel at (dx, dy), which are the screen pixel coordinate offsets from the center of the Sky pixmap.

Parameters

p	the screen pixel position to convert
LST	pointer to the local sidereal time, as a dms object.
lat	pointer to the current geographic laitude, as a dms object
onlyAltAz	the returned SkyPoint's RA & DEC are not computed, only Alt/Az.

N.B. We don't cache these sin/cos values in the inverse projection because it causes 'shaking' when moving the sky.

Reimplemented in EquirectangularProjector.

Definition at line 460 of file projector.cpp.

groundPoly()

QVector< Eigen::Vector2f > Projector::groundPoly ( SkyPoint * labelpoint = nullptr, bool * drawLabel = nullptr ) const

virtual

Get the ground polygon.

Parameters

labelpoint	This point will be set to something suitable for attaching a label
drawLabel	this tells whether to draw a label.

Returns

the ground polygon

Reimplemented in EquirectangularProjector.

Definition at line 313 of file projector.cpp.

onScreen() [1/2]

bool Projector::onScreen

(

const Eigen::Vector2f &

p

)

const

Definition at line 103 of file projector.cpp.

onScreen() [2/2]

bool Projector::onScreen

(

const QPointF &

p

)

const

Check whether the projected point is on-screen.

Definition at line 98 of file projector.cpp.

pointAt()

SkyPoint Projector::pointAt ( double az )

staticprotected

Helper function for drawing ground.

Returns

the point with Alt = 0, az = az

Definition at line 29 of file projector.cpp.

projectionK()

virtual double Projector::projectionK ( double x ) const

inlineprotectedvirtual

This function handles some of the projection-specific code.

See also

toScreen()

Reimplemented in AzimuthalEquidistantProjector, GnomonicProjector, LambertProjector, OrthographicProjector, and StereographicProjector.

Definition at line 280 of file projector.h.

projectionL()

virtual double Projector::projectionL ( double x ) const

inlineprotectedvirtual

This function handles some of the projection-specific code.

See also

toScreen()

Reimplemented in AzimuthalEquidistantProjector, GnomonicProjector, LambertProjector, OrthographicProjector, and StereographicProjector.

Definition at line 289 of file projector.h.

radius()

virtual double Projector::radius ( ) const

inlineprotectedvirtual

Get the radius of this projection's sky circle.

Returns

the radius in radians

Reimplemented in AzimuthalEquidistantProjector, EquirectangularProjector, GnomonicProjector, LambertProjector, OrthographicProjector, and StereographicProjector.

Definition at line 271 of file projector.h.

rst()

Eigen::Vector2f Projector::rst ( double x, double y ) const

inlineprotected

Transform proj (x, y) to screen (x, y) accounting for scale and rotation.

Transforms the Cartesian position given by the projector algorithm into the screen coordinate by applying the scale factor, rotation and shift from SkyMap origin

rst stands for rotate-scale-translate

Definition at line 314 of file projector.h.

setViewParams()

void Projector::setViewParams

(

const ViewParams &

p

)

Update cached values for projector.

Precompute cached values

Definition at line 46 of file projector.cpp.

toScreen()

QPointF Projector::toScreen	(	const SkyPoint *	o,
		bool	oRefract = true,
		bool *	onVisibleHemisphere = nullptr ) const

This is exactly the same as toScreenVec but it returns a QPointF.

It just calls toScreenVec and converts the result.

See also

toScreenVec()

Definition at line 93 of file projector.cpp.

toScreenVec()

Eigen::Vector2f Projector::toScreenVec ( const SkyPoint * o, bool oRefract = true, bool * onVisibleHemisphere = nullptr ) const

virtual

Given the coordinates of the SkyPoint argument, determine the pixel coordinates in the SkyMap.

Since most of the projections used by KStars are very similar, if this function were to be reimplemented in each projection subclass we would end up changing maybe 5 or 6 lines out of 150. Instead, we have a default implementation that uses the projectionK and projectionL functions to take care of the differences between e.g. Orthographic and Stereographic. There is also the cosMaxFieldAngle function, which is used for testing whether a point is on the visible part of the projection, and the radius function which gives the radius of the projection in screen coordinates.

While this seems ugly, it is less ugly than duplicating 150 loc to change 5.

Returns

Eigen::Vector2f containing screen pixel x, y coordinates of SkyPoint.

Parameters

o	pointer to the SkyPoint for which to calculate x, y coordinates.
oRefract	true = use Options::useRefraction() value. false = do not use refraction. This argument is only needed for the Horizon, which should never be refracted.
onVisibleHemisphere	pointer to a bool to indicate whether the point is on the visible part of the Celestial Sphere.

Reimplemented in EquirectangularProjector.

Definition at line 517 of file projector.cpp.

type()

virtual Q_INVOKABLE Projection Projector::type ( ) const

pure virtual

Return the type of this projection.

Implemented in AzimuthalEquidistantProjector, EquirectangularProjector, GnomonicProjector, LambertProjector, OrthographicProjector, and StereographicProjector.

unusablePoint()

bool Projector::unusablePoint ( const QPointF & p ) const

virtual

Check if the current point on screen is a valid point on the sky.

This is needed to avoid a crash of the program if the user clicks on a point outside the sky (the corners of the sky map at the lowest zoom level are the invalid points).

Parameters

p	the screen pixel position

Reimplemented in EquirectangularProjector.

Definition at line 440 of file projector.cpp.

updateClipPoly()

void Projector::updateClipPoly ( )

virtual

updateClipPoly calculate the clipping polygen given the current FOV.

Reimplemented in EquirectangularProjector.

Definition at line 417 of file projector.cpp.

viewParams()

ViewParams Projector::viewParams ( ) const

inline

Definition at line 72 of file projector.h.

Member Data Documentation

m_clipPolygon

QPolygonF Projector::m_clipPolygon

protected

Definition at line 359 of file projector.h.

m_cosY0

double Projector::m_cosY0 { 0 }

protected

Definition at line 357 of file projector.h.

m_data

KStarsData* Projector::m_data { nullptr }

protected

Definition at line 354 of file projector.h.

m_fov

double Projector::m_fov { 0 }

protected

Definition at line 358 of file projector.h.

m_sinY0

double Projector::m_sinY0 { 0 }

protected

Definition at line 356 of file projector.h.

m_vp

ViewParams Projector::m_vp

protected

Definition at line 355 of file projector.h.

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

• projector.h
• projector.cpp