I'm trying to translate a library written in Javascript in order to implement it in Objective C for my iOS application.
The link to the JavaScript library : https://github.com/mourner/suncalc
I got different values for Moonrise and Moonset.
The Javascript library returns :
moonrise = Mon Nov 28 2016 06:43:49 GMT+0100 (CET)
moonset = Mon Nov 28 2016 17:10:33 GMT+0100 (CET)
My Objective C implementation returns :
moonrise : 2016-11-28 02:00:00 +0000
moonset : 2016-11-28 01:00:00 +0000
I'm facing an issue with this functions :
// date/time constants and conversions
var dayMs = 1000 * 60 * 60 * 24,
J1970 = 2440588,
J2000 = 2451545;
function toJulian(date) { return date.valueOf() / dayMs - 0.5 + J1970; }
function toDays(date) { return toJulian(date) - J2000; }
function hoursLater(date, h) {
return new Date(date.valueOf() + h * dayMs / 24);
}
My Objective C implementation :
// date/time constants and conversions
#define dayMS 1000 * 60 * 60 * 24
#define J1970 2440588
#define J2000 2451545
-(double)toJulian:(NSDate *) date
{
return ([date timeIntervalSince1970] * 1000) / dayMS - 0.5 + J1970;
}
-(double)toDays:(NSDate *) date
{
double tj = [self toJulian:date];
return tj - J2000;
}
-(NSDate *)hoursLater:(NSDate *) date :(int) h
{
double d = ([date timeIntervalSince1970] * 1000) + h * dayMS / 24;
NSTimeInterval seconds = d / 1000;
NSDate *newDate = [NSDate dateWithTimeIntervalSince1970:seconds];
return newDate;
}
I can't see any mistakes, but my values are false.
Test Example :
Javascript Test
var date = new Date();
var d = toDays(date);
console.log("d = " + d);
d = 6175.947204432916
Objective C Test
NSDate *today = [NSDate date];
double d = [self toDays:today];
NSLog(@"d = %f", d);
d = 127900386826537.265625
If you find something, please let me know.
The issue is on the #define
definition.
#define dayMS 1000 * 60 * 60 * 24
#define J1970 2440588
#define J2000 2451545
-(double)toJulian:(NSDate *) date
{
return ([date timeIntervalSince1970] * 1000) / dayMS - 0.5 + J1970;
}
This is translated with:
-(double)toJulian:(NSDate *) date
{
return ([date timeIntervalSince1970] * 1000) / 1000 * 60 * 60 * 24 - 0.5 + 2440588;
}
It simply replace exactly the values.
But ([date timeIntervalSince1970] * 1000) / 1000 * 60 * 60 * 24
is different of ([date timeIntervalSince1970] * 1000) / (1000 * 60 * 60 * 24)
.
A quick solution:
return ([date timeIntervalSince1970] * 1000) / (dayMS) - 0.5 + J1970;`
Or you can put the parenthesis in the #define
:
#define dayMS (1000 * 60 * 60 * 24)
Another solution (I don't really like #define) and you don't need the parenthesis anymore:
const double dayMS = 1000 * 60 * 60 * 24;