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author | Mattias Andrée <m@maandree.se> | 2024-10-20 17:28:46 +0200 |
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committer | Mattias Andrée <m@maandree.se> | 2024-10-20 17:28:46 +0200 |
commit | 09e6857ae73249bc7433f2971dcf291c70e4c766 (patch) | |
tree | f07ef152c6372083ab87e2e4289c7ab8b1f2c1ad /libtellurian_elevated_gravity.3 | |
parent | Third commit (diff) | |
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Fourth commit
Signed-off-by: Mattias Andrée <m@maandree.se>
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-rw-r--r-- | libtellurian_elevated_gravity.3 | 96 |
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diff --git a/libtellurian_elevated_gravity.3 b/libtellurian_elevated_gravity.3 new file mode 100644 index 0000000..fb728b9 --- /dev/null +++ b/libtellurian_elevated_gravity.3 @@ -0,0 +1,96 @@ +.TH LIBTELLURIAN_ELEVATED_GRAVITY 3 libtellurian +.SH NAME +libtellurian_elevated_gravity \- Calculate gravity at some altitude + +.SH SYNPOSIS +.nf +#include <libtellurian.h> + +double libtellurian_elevated_gravity(double \fIgravity\fP, double \fIlatitude\fP, double \fIaltitude\fP); + +double libtellurian_elevated_gravity_radians(double \fIgravity\fP, double \fIlatitude\fP, double \fIaltitude\fP); +.fi +.PP +Link with +.I -ltellurian +.IR -lm . + +.SH DESCRIPTION +The +.BR libtellurian_elevated_gravity () +function models the Earth as a spheroid and calculates +the gravity at a given +.I altitude +and +.IR latitude , +given the +.I gravity +at zero-altitude on the same +.IR latitude . +.PP +The +.I latitude +shall be specified according to GPS and in degrees +and the +.I gravity +shall be specified in meters per square second. +However the +.I altitude +shall be the number of metres above a reference datum +for which the input +.I gravity +applies. For the normal gravity, this would be the +geocentric radius as calculated by the +.BR libtellurian_sea_level (3) +function, and so the +.I altitude +would be the altitude reported in raw GPS measurements, +howver, for real world gravity, this would typically +be the orthometric altitude. +.PP +The +.BR libtellurian_elevated_gravity_radians () +function is identical to the +.BR libtellurian_elevated_gravity () +function except that +.I latitude +shall be specified in radians. + +.SH RETURN VALUE +The +.BR libtellurian_elevated_gravity () +and +.BR libtellurian_elevated_gravity_radians () +functions return the normal gravity, at the specified +latitude, measured in meters per square second. + +.SH ERRORS +None. + +.SH NOTES +Some GPS systems, espcially those for hiking, surveying, +and aviation, report orthometric height (height above +sea level), rather than ellipsoidal height to make it +easier for the user to interpret. +.PP +The +.BR libtellurian_normal_gravity (3) +function does not account for the Earth's rotation, +however, the +.BR libtellurian_elevated_gravity () +function does account for the Earth's rotation. +Given a normal gravity, it should for first be corrected +for the rotation of the Earth, using the +.BR libtellurian_effective_gravity (3) +function, before it is input to the +.BR libtellurian_elevated_gravity () +function. +.PP +The adjustment this function creates is useful for +common heights in aviation, does not work for outer +space. + +.SH SEE ALSO +.BR libtellurian (7), +.BR libtellurian_effective_gravity (3), +.BR libtellurian_normal_gravity (3) |