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37084a156d
Implemented the C function Astronomy_ObserverGravity. It implements the WGS 84 Ellipsoidal Gravity Formula, yielding the effective observed gravitational acceleration at a location on or above the Earth's surface. Wrote a demo program that also serves as a unit test. I verified a few of the calculations, so the file demo/c/test/gravity_correct.txt also serves as correct unit test output.
52 lines
1.5 KiB
C
52 lines
1.5 KiB
C
/*
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gravity.c - Don Cross - 2021-07-19
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Example C program for Astronomy Engine:
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https://github.com/cosinekitty/astronomy
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*/
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#include <stdio.h>
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#include <math.h>
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#include "astronomy.h"
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const char * const UsageText =
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"\n"
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" USAGE:\n"
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"\n"
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" gravity latitude height\n"
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"\n"
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" Calculates the gravitational acceleration experienced\n"
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" by an observer on the surface of the Earth at the specified\n"
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" latitude (degrees north of the equator) and height\n"
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" (meters above sea level).\n"
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" The output is the gravitational acceleration in m/s^2.\n"
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"\n";
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int main(int argc, const char *argv[])
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{
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const double MAX_HEIGHT_METERS = 100000.0;
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double latitude, height, gravity;
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if (argc != 3)
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{
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fprintf(stderr, "%s", UsageText);
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return 1;
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}
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if (1 != sscanf(argv[1], "%lf", &latitude) || !isfinite(latitude) || latitude < -90.0 || latitude > +90.0)
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{
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fprintf(stderr, "ERROR: Invalid latitude '%s'. Must be a number between -90 and +90.\n", argv[1]);
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return 1;
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}
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if (1 != sscanf(argv[2], "%lf", &height) || !isfinite(height) || height < 0.0 || height > MAX_HEIGHT_METERS)
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{
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fprintf(stderr, "ERROR: Invalid height '%s'. Must be a number of meters between 0 and %0.0lf.\n", argv[2], MAX_HEIGHT_METERS);
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return 1;
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}
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gravity = Astronomy_ObserverGravity(latitude, height);
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printf("latitude = %8.4lf, height = %6.0lf, gravity = %8.6lf\n", latitude, height, gravity);
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return 0;
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}
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