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Fix phase of moon calculation

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The reported phase was often one day early because calculations were
based on midnight. For full and new moon this is changed to noon. For
first and last quarter a direct check of the appearance of the half moon
during the selected day is performed.

Comments are relocated and expanded.

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>
This commit is contained in:
Lars Henriksen 2017-09-03 01:27:23 +02:00 committed by Lukas Fleischer
parent 3095bf4214
commit 90fe21af88
1 changed files with 31 additions and 28 deletions
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59
src/ui-calendar.c
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@ -842,9 +842,23 @@ static void adj360(double *deg)
break;
}
/*
* Phase of the Moon. Calculates the current phase of the moon.
* Based on routines from `Practical Astronomy with Your Calculator',
* by Duffett-Smith. Comments give the section from the book that
* particular piece of code was adapted from.
*
* -- Keith E. Brandt VIII 1984
*
* Updated to the Third Edition of Duffett-Smith's book, IX 1998
*
*/
/*
* potm --
* return phase of the moon
* given number of days since January 1st 1990, 00:00
* (incl. hours and minutes as a fraction of a day),
* return phase of the moon as a percentage.
*/
static double potm(double days)
{
@ -877,17 +891,6 @@ static double potm(double days)
return 50.0 * (1 - cos(dtor(D))); /* sec 67 #3 */
}
/*
* Phase of the Moon. Calculates the current phase of the moon.
* Based on routines from `Practical Astronomy with Your Calculator',
* by Duffett-Smith. Comments give the section from the book that
* particular piece of code was adapted from.
*
* -- Keith E. Brandt VIII 1984
*
* Updated to the Third Edition of Duffett-Smith's book, IX 1998
*
*/
static double pom(time_t tmpt)
{
struct tm *GMT;
@ -908,30 +911,30 @@ static double pom(time_t tmpt)
/*
* Return a pictogram representing the current phase of the moon.
* Careful: date is the selected day in calendar at 00:00, so it represents
* the phase of the moon for previous day.
* Careful: date is the selected day in calendar at 00:00,
* and so represents the phase of the moon at midnight.
*/
const char *ui_calendar_get_pom(time_t date)
{
const char *pom_pict[MOON_PHASES] =
{ " ", "|) ", "(|)", "(| ", " | " };
enum pom phase = NO_POM;
double pom_today, relative_pom, pom_yesterday, pom_tomorrow;
const double half = 50.0;
pom_yesterday = pom(date);
pom_today = pom(date + DAYINSEC);
relative_pom = abs(pom_today - half);
pom_tomorrow = pom(date + 2 * DAYINSEC);
if (pom_today > pom_yesterday && pom_today > pom_tomorrow)
phase = FULL_MOON;
else if (pom_today < pom_yesterday && pom_today < pom_tomorrow)
phase = NEW_MOON;
else if (relative_pom < abs(pom_yesterday - half)
&& relative_pom < abs(pom_tomorrow - half))
phase =
(pom_tomorrow >
pom_today) ? FIRST_QUARTER : LAST_QUARTER;
date += DAYINSEC / 2; /* adjust to noon */
double pom_n_b = pom(date - DAYINSEC); /* noon before */
double pom_m_b = pom(date - DAYINSEC / 2); /* midnight before */
double pom_n = pom(date); /* noon */
double pom_m_a = pom(date + DAYINSEC / 2); /* midnight after */
double pom_n_a = pom(date + DAYINSEC); /* noon after */
if (pom_n > pom_n_b && pom_n > pom_n_a)
phase = FULL_MOON;
else if (pom_n < pom_n_b && pom_n < pom_n_a)
phase = NEW_MOON;
else if (pom_m_b < half && half < pom_m_a)
phase = FIRST_QUARTER;
else if (pom_m_b > half && half > pom_m_a)
phase = LAST_QUARTER;
return pom_pict[phase];
}