Projector
#include <projector.h>
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 56 of file projector.h.
Constructor & Destructor Documentation
◆ Projector()

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 offscreen, 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 onscreen it is computationally expensive to determine whether a particular position is onscreen 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 onscreen 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 2degree 'safety factor'
Definition at line 183 of file projector.cpp.
◆ clipLine()
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()
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()

virtual 
 Returns
 the clipping polygen covering the visible sky area. Anything outside this polygon is clipped by QPainter.
Definition at line 424 of file projector.cpp.
◆ cosMaxFieldAngle()

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.
Definition at line 295 of file projector.h.
◆ derst()

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 rotatescaletranslate
 See also
 rst
Definition at line 331 of file projector.h.
◆ findNorthPA()
double Projector::findNorthPA  (  const SkyPoint *  o, 
float  x,  
float  y  
)  const 
Determine the onscreen 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 Yaxis). 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 Yaxis of the line connecting the object to its test point.
Definition at line 237 of file projector.cpp.
◆ findPA()
double Projector::findPA  (  const SkyObject *  o, 
float  x,  
float  y  
)  const 
Determine the onscreen 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 Yaxis). 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 Yaxis of the line connecting the object to its test point.
Definition at line 267 of file projector.cpp.
◆ findZenithPA()
double Projector::findZenithPA  (  const SkyPoint *  o, 
float  x,  
float  y  
)  const 
Determine the onscreen 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 Yaxis of the line connecting the object to its test point.
Definition at line 273 of file projector.cpp.
◆ fov()
double Projector::fov  (  )  const 
Return the FOV of this projection.
Definition at line 88 of file projector.cpp.
◆ fromScreen()

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 449 of file projector.cpp.
◆ groundPoly()

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 305 of file projector.cpp.
◆ onScreen()
bool Projector::onScreen  (  const QPointF &  p  )  const 
Check whether the projected point is onscreen.
Definition at line 98 of file projector.cpp.
◆ pointAt()

staticprotected 
Helper function for drawing ground.
 Returns
 the point with Alt = 0, az =
az
Definition at line 29 of file projector.cpp.
◆ projectionK()

inlineprotectedvirtual 
This function handles some of the projectionspecific code.
 See also
 toScreen()
Reimplemented in LambertProjector, AzimuthalEquidistantProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.
Definition at line 276 of file projector.h.
◆ projectionL()

inlineprotectedvirtual 
This function handles some of the projectionspecific code.
 See also
 toScreen()
Reimplemented in LambertProjector, AzimuthalEquidistantProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.
Definition at line 285 of file projector.h.
◆ radius()

inlineprotectedvirtual 
Get the radius of this projection's sky circle.
 Returns
 the radius in radians
Reimplemented in LambertProjector, AzimuthalEquidistantProjector, EquirectangularProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.
Definition at line 267 of file projector.h.
◆ rst()

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 rotatescaletranslate
Definition at line 310 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()

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 506 of file projector.cpp.
◆ type()

pure virtual 
Return the type of this projection.
Implemented in LambertProjector, AzimuthalEquidistantProjector, EquirectangularProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.
◆ unusablePoint()

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 429 of file projector.cpp.
◆ updateClipPoly()

virtual 
updateClipPoly calculate the clipping polygen given the current FOV.
Reimplemented in EquirectangularProjector.
Definition at line 406 of file projector.cpp.
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