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/*
NASA/TRMM, Code 910.1.
This is the TRMM Office Radar Software Library.
Copyright (C) 1996, 1997
John H. Merritt
Space Applications Corporation
Vienna, Virginia
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free
Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <stdio.h>
#include <math.h>
#include "rsl.h"
# define M_PI 3.14159265358979323846
# define M_PI_2 1.57079632679489661923
/* Earth radius in km. */
double Re = (6374.0*4.0/3.0);
/********************************************************************/
/* */
/* RSL_set_earth_rad(double new_Re) */
/* */
/* By: Dennis Flanigan */
/* Applied Research Corporation */
/* August 26, 1994 */
/********************************************************************/
void RSL_set_earth_radius(double new_Re)
{
Re = new_Re;
}
/*********************************************************************/
/* */
/* void RSL_get_gr_slantr_h */
/* *gr - ground range in KM. */
/* *slantr - slant range in KM. */
/* *h - height in KM. */
/* */
/* By: John Merritt */
/* June 7, 1995 */
/*********************************************************************/
void RSL_get_gr_slantr_h(Ray *ray, int i, float *gr, float *slantr, float *h)
{
*gr = *slantr = *h = 0.0;
if (ray == NULL) return;
*slantr = i * ray->h.gate_size + ray->h.range_bin1;
*slantr /= 1000; /* meters to km */
RSL_get_groundr_and_h(*slantr, ray->h.elev, gr, h);
return;
}
/*********************************************************************/
/* */
/* RSL_get_groundr_and_h(sr, elev, &gr, &h) */
/* */
/* By: John Merritt */
/* Space Applications Corporation */
/* July 23, 1994 */
/*********************************************************************/
void RSL_get_groundr_and_h(float slant_r, float elev, float *gr, float *h)
{
/* Input:
* slant_r - slant range, along the beam, in km.
* elev - elevation angle, in degrees.
*
* Output:
* gr - Ground range in km.
* h - Height of data point above earth, in km.
*/
double GR;
double H;
if (slant_r == 0.0) {*h = 0; *gr = 0; return;}
elev += 90;
H = sqrt( pow(Re,2.0) + pow(slant_r,2.0) - 2*Re*slant_r*cos(elev*M_PI/180.0));
if (H != 0.0) {
GR = Re * acos( ( pow(Re,2.0) + pow(H,2.0) - pow(slant_r,2.0)) / (2 * Re * H));
} else {
GR = slant_r;
H = Re;
}
H -= Re;
*h = H;
*gr = GR;
}
/*********************************************************************/
/* */
/* RSL_get_slantr_and_elev(gr, h, &r, &e) */
/* */
/* By: John Merritt */
/* Space Applications Corporation */
/* July 23, 1994 */
/* */
/*********************************************************************/
void RSL_get_slantr_and_elev(float gr, float h, float *slant_r, float *elev)
{
/* Input:
* gr - Ground range in km.
* h - Height of data point above earth, in km.
*
* Output:
* slant_r - slant range, along the beam, in km.
* elev - elevation angle, in degrees.
*/
/* This equation lifted from Dennis Flanigan's rsph.c code. */
double slant_r_2; /* Slant range squared. */
double ELEV;
double SLANTR;
if (gr == 0) {*slant_r = 0; *elev = 0; return;}
h += Re;
slant_r_2 = pow(Re,2.0) + pow(h,2.0) - (2*Re*h*cos(gr/Re));
SLANTR = sqrt(slant_r_2);
ELEV = acos( (pow(Re,2.0) + slant_r_2 - pow(h,2.0)) / (2*Re*(SLANTR)));
ELEV *= 180.0/M_PI;
ELEV -= 90.0;
*slant_r = SLANTR;
*elev = ELEV;
}
/*********************************************************************/
/* */
/* RSL_get_slantr_and_h(gr, elev, &sr, &h) */
/* */
/* By: John Merritt */
/* Space Applications Corporation */
/* July 23, 1994 */
/* */
/*********************************************************************/
void RSL_get_slantr_and_h(float gr, float elev, float *slant_r, float *h)
{
/* Input:
* gr - Ground range in km.
* elev - elevation angle, in degrees.
*
* Output:
* slant_r - slant range, along the beam, in km.
* h - Height of data point above earth, in km.
*/
double ELEV;
double SLANTR;
double ALPHA;
double BETA;
double GAMMA;
double A;
if (gr == 0) {*slant_r = 0; *h = 0; return;}
ELEV = elev*M_PI/180.0;
ALPHA = ELEV + M_PI_2; /* Elev angle + 90 */
GAMMA = gr/Re;
BETA = M_PI - (ALPHA + GAMMA); /* Angle made by Re+h and slant */
SLANTR = Re*(sin(GAMMA)/sin(BETA));
A = Re*sin(ALPHA)/sin(BETA);
*h = (float) (A - Re);
*slant_r = (float)SLANTR;
}
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