Projector

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#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 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
 
virtual double projectionK (double x) const
 
virtual double projectionL (double x) const
 
virtual double radius () const
 

Static Protected Member Functions

static SkyPoint pointAt (double az)
 

Protected Attributes

QPolygonF m_clipPolygon
 
double m_cosY0 { 0 }
 
KStarsDatam_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 55 of file projector.h.

Constructor & Destructor Documentation

◆ Projector()

Projector::Projector ( const ViewParams p)
explicit

Constructor.

Parameters
pthe 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
ppointer 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 385 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.

Definition at line 281 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.

Definition at line 237 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 265 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
pthe screen pixel position to convert
LSTpointer to the local sidereal time, as a dms object.
latpointer to the current geographic laitude, as a dms object
onlyAltAzthe 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 406 of file projector.cpp.

◆ groundPoly()

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

Get the ground polygon.

Parameters
labelpointThis point will be set to something suitable for attaching a label
drawLabelthis tells whether to draw a label.
Returns
the ground polygon

Reimplemented in EquirectangularProjector.

Definition at line 270 of file projector.cpp.

◆ onScreen()

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 LambertProjector, AzimuthalEquidistantProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.

Definition at line 262 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 LambertProjector, AzimuthalEquidistantProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.

Definition at line 271 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 LambertProjector, AzimuthalEquidistantProjector, EquirectangularProjector, GnomonicProjector, OrthographicProjector, and StereographicProjector.

Definition at line 253 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
opointer to the SkyPoint for which to calculate x, y coordinates.
oRefracttrue = use Options::useRefraction() value. false = do not use refraction. This argument is only needed for the Horizon, which should never be refracted.
onVisibleHemispherepointer to a bool to indicate whether the point is on the visible part of the Celestial Sphere.

Reimplemented in EquirectangularProjector.

Definition at line 463 of file projector.cpp.

◆ type()

virtual Q_INVOKABLE Projection Projector::type ( ) const
pure virtual

◆ 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
pthe screen pixel position

Reimplemented in EquirectangularProjector.

Definition at line 390 of file projector.cpp.

◆ updateClipPoly()

void Projector::updateClipPoly ( )
virtual

updateClipPoly calculate the clipping polygen given the current FOV.

Reimplemented in EquirectangularProjector.

Definition at line 367 of file projector.cpp.


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