106 lines
3.2 KiB
C
106 lines
3.2 KiB
C
/**************************************************************************
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* polar.c -- routines to deal with polar math and transformations
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*
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* Written by Curtis Olson, started June 1997.
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*
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* Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* $Id$
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* (Log is kept at end of this file)
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**************************************************************************/
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#include <math.h>
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#include <stdio.h>
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#include "polar.h"
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#include "../constants.h"
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/* we can save these values between calls for efficiency */
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static double st, ct, sp, cp;
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/* Convert a geodetic coordinate to a cartesian coordinat on the unit
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* circle, scaled by the radius of the earth in meters. Ignores Altitude,
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* since this is just for translating points around on the surface. */
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struct fgCartesianPoint fgGeodetic2Cartesian(double lon, double lat) {
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struct fgCartesianPoint pnew;
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pnew.x = cos(lon) * cos(lat) * EARTH_RAD;
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pnew.y = sin(lon) * cos(lat) * EARTH_RAD;
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pnew.z = sin(lat) * EARTH_RAD;
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return(pnew);
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}
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/* Precalculate as much as possible so we can do a batch of transforms
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* through the same angles, will rotates a cartesian point about the
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* center of the earth by Theta (longitude axis) and Phi (latitude
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* axis) */
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/* Here are the unoptimized transformation equations
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x' = cos(Phi) * cos(Theta) * x + cos(Phi) * sin(Theta) * y +
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sin(Phi) * z
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y' = -sin(Theta) * x + cos(Theta) * y
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z' = -sin(Phi) * sin(Theta) * y - sin(Phi) * cos(Theta) * x +
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cos(Phi) * z;
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*/
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void fgRotateBatchInit(double Theta, double Phi) {
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printf("Theta = %.3f, Phi = %.3f\n", Theta, Phi);
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st = sin(Theta);
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ct = cos(Theta);
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sp = sin(-Phi);
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cp = cos(-Phi);
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}
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/* Rotates a cartesian point about the center of the earth by Theta
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* (longitude axis) and Phi (latitude axis) */
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struct fgCartesianPoint fgRotateCartesianPoint(struct fgCartesianPoint p) {
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struct fgCartesianPoint p1, p2;
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/* printf("start = %.3f %.3f %.3f\n", p.x, p.y, p.z); */
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/* rotate about the z axis */
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p1.x = ct * p.x - st * p.y;
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p1.y = st * p.x + ct * p.y;
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p1.z = p.z;
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/* printf("step 1 = %.3f %.3f %.3f\n", p1.x, p1.y, p1.z); */
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/* rotate new point about y axis */
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p2.x = cp * p1.x + sp * p1.z;
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p2.y = p1.y;
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p2.z = cp * p1.z - sp * p1.x;
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/* printf("cp = %.5f, sp = %.5f\n", cp, sp); */
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/* printf("(1) = %.5f, (2) = %.5f\n", cp * p1.z, sp * p1.x); */
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/* printf("step 2 = %.3f %.3f %.3f\n", p2.x, p2.y, p2.z); */
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return(p2);
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}
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/* $Log$
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/* Revision 1.1 1997/07/07 21:02:36 curt
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/* Initial revision.
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/* */
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