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.TH LIBRED_SOLAR_ELEVATION 3 LIBRED
.SH NAME
libred_solar_elevation \- Calculate the Sun's apparent elevation
.SH SYNOPSIS
.nf
#include <libred.h>
double \fBlibred_solar_elevation\fP(double \fIlatitude\fP, double \fIlongitude\fP);
.fi
.PP
Link with
.IR -lred .
.SH DESCRIPTION
.B libred_solar_elevation
calculates the Sun's elevation as apparent from a select geographical position.
Namely from
.I latitude
degrees north of GPS's equator and
.I longitude
degrees east of GPS's prime meridian. The function is only explicitly defined for
values between -90 and +90 for
.I latitude
and values between -180 and +180 for and
.IR longitude .
Other values may or may not work, no error is thrown if used.
.SH "RETURN VALUE"
Upon successful completion, the function sets
.B errno
to 0 and returns the Sun's current apparent elevation, measured in
degrees above the horizon. On failure, the function returns an
arbitrary value (happens to always be 0.0) and sets
.B errno
an a non-zero value.
.SH ERRORS
The function may fail for any reason specified for
.BR clock_gettime (3),
and set the value of
.B errno
to the same values.
.B errno
is always set to 0 on success.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.BR libred.h (0),
.BR libred (7),
.BR libred_check_timetravel (3),
.BR libred_init_colour (3)
.SH LICENSE
Copyright \(co 2016 Mattias Andrée
.br
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
.br
This is free software: you are free to change and redistribute it.
.br
There is NO WARRANTY, to the extent permitted by law.
.PP
Copying and distribution of this manual, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved. This file is offered as-is,
without any warranty.
.SH BUGS
Please report bugs to <https://github.com/maandree/libred/issues>
or to <maandree@member.fsf.org>.
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