Grids: accurate ecliptic calendar marks

guide/ch_astronomical_concepts.tex

@@ -270,6 +270,7 @@ \subsection{Ecliptical Coordinates}
 
 The Earth's orbit around the Sun, i.e., the \indexterm{ecliptic},
 defines the ``equatorial line'' of this coordinate system, which is traditionally used when computing the coordinates for planets because of their close proximity to this line.
+Mirroring Earth's motion, the Sun is seen to move along the ecliptic. 
 
 The zero point of \indexterm{ecliptical longitude} $\lambda$ is the
 same as for equatorial coordinates (\Aries), and the \indexterm{ecliptical
@@ -286,11 +287,12 @@ \subsection{Ecliptical Coordinates}
 In addition, \indexterm[obliquity, ecliptic]{ecliptic obliquity} against the equatorial coordinates,
 which mirrors the Earth's axial tilt, slowly changes.
 
-Therefore, also for ecliptical coordinates is is required to specify
+Therefore, also for ecliptical coordinates it is required to specify
 which date (epoch) the coordinates refer to.  Stellarium can draw grids
 for two epochs. Use the \key{,} key to draw the \indexterm{ecliptic}
 for the simulation time. The Markings dialog
-(\ref{sec:gui:view:markings}) allows you to also show a line for epoch
+(\ref{sec:gui:view:markings}) allows you to add date marks to the ecliptic 
+line \newFeature{23.1} and also show a line for epoch
 J2000.0 and grids for the ecliptical coordinates for current epoch and
 epoch J2000.0. You can assign your own shortcut keys
 (section~\ref{sec:gui:help:hotkeys}) if you frequently operate with
@@ -309,7 +311,7 @@ \subsection{Ecliptical Coordinates}
 ecliptic \indexterm[obliquity, ecliptic]{obliquity}. The real track of where Earth's axis is pointing forms an open helical loop.
 
 The inner planets are best observed when their apparent distance from
-the Sun, or \indexterm{elongation} reaches a maximum. Unfortunately
+the Sun, or \indexterm{elongation}, reaches a maximum. Unfortunately
 there are two definitions for elongation, though:
 \begin{description}
 \item[$\psi$] angular distance on the sphere. This is today the most widely used definition.

guide/ch_interface.tex

@@ -696,7 +696,7 @@ \subsection{The Solar System Objects (SSO) Tab}
 \end{figure}
 
 \begin{figure}[p]
-\centering\includegraphics[width=0.75\textwidth]{view_dialog_markings_tab.png}
+\centering\includegraphics[width=0.75\textwidth]{view_dialog_markings_tab.jpg}
 \caption{View Settings Window: Markings Tab}
 \label{fig:gui:view:markings}
 \end{figure}
@@ -732,13 +732,13 @@ \subsection{The Markings Tab}
 \label{sec:gui:view:markings}
 
 \noindent The Markings tab of the View window
-(Fig.~\ref{fig:gui:view:markings}) controls plot various grids and
-lines on celestial sphere. Colors for grids, lines and points can be
+(Fig.~\ref{fig:gui:view:markings}) controls plotting various grids and
+lines on the celestial sphere. Colors for grids, lines and points can be
 adjusted by clicking on the corresponding colored square.  The central
 column governs lines like equator, ecliptic, meridian etc., where each
 can optionally be fine-tuned to \newFeature{0.20.0} show partition
 marks and labels. Color settings are stored immediately, all other
-flags need an explicit saving of the settings (see section
+flags need explicit saving of the settings (see section
 \ref{sec:gui:configuration:main}).
 
 \subsection{The Landscape Tab}

src/core/StelCore.hpp

@@ -811,7 +811,7 @@ public slots:
 	//! This signal is emitted when the date has changed for a month.
 	void dateChangedForMonth();
 	//! This signal is emitted when the date has changed by one year.
-	void dateChangedByYear();
+	void dateChangedByYear(const int year);
 	//! This signal indicates a horizontal display flip
 	void flipHorzChanged(bool b);
 	//! This signal indicates a vertical display flip

src/core/StelMovementMgr.cpp

@@ -537,11 +537,12 @@ void StelMovementMgr::handleMouseWheel(QWheelEvent* event)
 			double jdNow=core->getJD();
 			int year, month, day, hour, min, sec, millis;
 			StelUtils::getDateTimeFromJulianDay(jdNow, &year, &month, &day, &hour, &min, &sec, &millis);
+			year+=qRound(numSteps);
 			double jdNew;
-			StelUtils::getJDFromDate(&jdNew, year+qRound(numSteps), month, day, hour, min, static_cast<float>(sec));
+			StelUtils::getJDFromDate(&jdNew, year, month, day, hour, min, static_cast<float>(sec));
 			core->setJD(jdNew);
 			emit core->dateChanged();			
-			emit core->dateChangedByYear();
+			emit core->dateChangedByYear(year);
 		}
 		else if (event->modifiers() & Qt::AltModifier)
 		{

src/core/StelUtils.cpp

@@ -1147,10 +1147,21 @@ bool isLeapYear(const int year)
 // Meeus, AA 2nd, 1998, ch.7 p.65
 int dayInYear(const int year, const int month, const int day)
 {
-	int k=(isLeapYear(year) ? 1:2);
+	const int k=(isLeapYear(year) ? 1:2);
 	return static_cast<int>(275*month/9) - k*static_cast<int>((month+9)/12) + day -30;
 }
 
+// Find date from day number within year and the year.
+// Meeus, AA 2nd, 1998, ch.7 p.66
+Vec3i dateFromDayYear(const int day, const int year)
+{
+	const int k=(isLeapYear(year) ? 1:2);
+	int month = day<32 ? 1 : static_cast<int>(9.f*(k+day)/275.f+0.98f);
+
+	int monthDay = day - static_cast<int>(275.f*month/9.f) + k*static_cast<int>((month+9)/12.f) + 30;
+	return {year, month, monthDay};
+}
+
 // Return a fractional year like YYYY.ddddd. For negative years, the year number is of course decrease. E.g. -500.5 occurs in -501.
 double yearFraction(const int year, const int month, const double day)
 {

src/core/StelUtils.hpp

@@ -539,6 +539,10 @@ namespace StelUtils
 	//! Find day number for date in year.
 	//! Meeus, Astronomical Algorithms 2nd ed., 1998, ch.7, p.65
 	int dayInYear(const int year, const int month, const int day);
+	//! Find date from day number within year and the year.
+	//! Meeus, AA 2nd, 1998, ch.7 p.66
+	//! @returns Vec3i(year, month, day)
+	Vec3i dateFromDayYear(const int day, const int year);
 	//! Return a fractional year like YYYY.ddddd. For negative years, the year number is decreased. E.g. -500.5 occurs in -501.
 	double yearFraction(const int year, const int month, const double day);