1 /**************************************************************************
2 * polar.c -- routines to deal with polar math and transformations
4 * Written by Curtis Olson, started June 1997.
6 * Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2 of the
11 * License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
23 * (Log is kept at end of this file)
24 **************************************************************************/
31 #include "../constants.h"
34 /* we can save these values between calls for efficiency */
35 static double st, ct, sp, cp;
38 /* Convert a geodetic coordinate to a cartesian coordinat on the unit
39 * circle, scaled by the radius of the earth in meters. Ignores Altitude,
40 * since this is just for translating points around on the surface. */
41 struct fgCartesianPoint fgGeodetic2Cartesian(double lon, double lat) {
42 struct fgCartesianPoint pnew;
44 pnew.x = cos(lon) * cos(lat) * EARTH_RAD;
45 pnew.y = sin(lon) * cos(lat) * EARTH_RAD;
46 pnew.z = sin(lat) * EARTH_RAD;
52 /* Precalculate as much as possible so we can do a batch of transforms
53 * through the same angles, will rotates a cartesian point about the
54 * center of the earth by Theta (longitude axis) and Phi (latitude
57 /* Here are the unoptimized transformation equations
59 x' = cos(Phi) * cos(Theta) * x + cos(Phi) * sin(Theta) * y +
61 y' = -sin(Theta) * x + cos(Theta) * y
62 z' = -sin(Phi) * sin(Theta) * y - sin(Phi) * cos(Theta) * x +
66 void fgRotateBatchInit(double Theta, double Phi) {
67 printf("Theta = %.3f, Phi = %.3f\n", Theta, Phi);
75 /* Rotates a cartesian point about the center of the earth by Theta
76 * (longitude axis) and Phi (latitude axis) */
77 struct fgCartesianPoint fgRotateCartesianPoint(struct fgCartesianPoint p) {
78 struct fgCartesianPoint p1, p2;
80 /* printf("start = %.3f %.3f %.3f\n", p.x, p.y, p.z); */
82 /* rotate about the z axis */
83 p1.x = ct * p.x - st * p.y;
84 p1.y = st * p.x + ct * p.y;
87 /* printf("step 1 = %.3f %.3f %.3f\n", p1.x, p1.y, p1.z); */
89 /* rotate new point about y axis */
90 p2.x = cp * p1.x + sp * p1.z;
92 p2.z = cp * p1.z - sp * p1.x;
94 /* printf("cp = %.5f, sp = %.5f\n", cp, sp); */
95 /* printf("(1) = %.5f, (2) = %.5f\n", cp * p1.z, sp * p1.x); */
97 /* printf("step 2 = %.3f %.3f %.3f\n", p2.x, p2.y, p2.z); */
104 /* Revision 1.1 1997/07/07 21:02:36 curt