1 // constants.h -- various constant definitions
2 //
3 // Written by Curtis Olson, started February 2000.
4 // Last change by Eric van den Berg, Feb 2013
5 //
6 // Copyright (C) 2000  Curtis L. Olson - http://www.flightgear.org/~curt/
7 //
8 // This library is free software; you can redistribute it and/or
9 // modify it under the terms of the GNU Library General Public
10 // License as published by the Free Software Foundation; either
11 // version 2 of the License, or (at your option) any later version.
12 //
13 // This library is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
16 // Library General Public License for more details.
17 //
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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
21 //
22 // $Id$
23 
24 /** \file constants.h
25  * Various constant definitions.
26  */
27 
28 
29 #ifndef _SG_CONSTANTS_H
30 #define _SG_CONSTANTS_H
31 
32 
33 #include <simgear/compiler.h>
34 
35 #include <cmath>
36 
37 
38 // Make sure PI is defined in its various forms
39 
40 #ifndef SGD_PI // remove me once FlightGear no longer uses PLIB
41 
42 #ifdef M_PI
43 const double SGD_PI = M_PI;
44 const float SG_PI = M_PI;
45 #else
46 const float SG_PI = 3.1415926535f;
47 const double SGD_PI = 3.1415926535;
48 #endif
49 
50 #endif // of PLIB-SG guard
51 
52 /** 2 * PI */
53 const double SGD_2PI = SGD_PI * 2.0;
54 
55 /** PI / 2 */
56 #ifdef M_PI_2
57 #  define  SGD_PI_2  M_PI_2
58 #else
59 #  define  SGD_PI_2  1.57079632679489661923
60 #endif
61 
62 /** PI / 4 */
63 const double SGD_PI_4 = 0.78539816339744830961;
64 
65 #ifndef SGD_DEGREES_TO_RADIANS // // remove me once FlightGear no longer uses PLIB
66 
67 const double SGD_DEGREES_TO_RADIANS = SGD_PI / 180.0;
68 const double SGD_RADIANS_TO_DEGREES = 180.0 / SGD_PI;
69 
70 const float SG_DEGREES_TO_RADIANS = SG_PI / 180.0f;
71 const float SG_RADIANS_TO_DEGREES = 180.0f / SG_PI;
72 
73 #endif // of PLIB-SG guard
74 
75 /** \def SG_E "e" */
76 #ifdef M_E
77 #  define SG_E     M_E
78 #else
79 #  define SG_E     2.7182818284590452354
80 #endif
81 
82 /** pi/180/60/60, or about 100 feet at earths' equator */
83 #define SG_ONE_SECOND 4.848136811E-6
84 
85 
86 /** Radius of Earth in kilometers at the equator.  Another source had
87  *  6378.165 but this is probably close enough */
88 #define SG_EARTH_RAD 6378.155
89 
90 // Maximum terrain elevation from sea level
91 #define SG_MAX_ELEVATION_M 9000.0
92 
93 // Earth parameters for WGS 84, taken from LaRCsim/ls_constants.h
94 
95 /** Value of earth radius from LaRCsim (ft) */
96 #define SG_EQUATORIAL_RADIUS_FT  20925650.
97 
98 /** Value of equatorial earth radius from LaRCsim (meter) */
99 #define SG_EQUATORIAL_RADIUS_M   6378138.12
100 
101 /** Radius squared (ft) */
102 #define SG_EQ_RAD_SQUARE_FT 437882827922500.
103 
104 /** Radius squared (meter) */
105 #define SG_EQ_RAD_SQUARE_M   40680645877797.1344
106 
107 /** Value of WGS84 polar earth radius (meter) */
108 #define SG_POLAR_RADIUS_M   6356752.3142451794975639668
109 
110 // Physical Constants, SI
111 
112 /**mean gravity on earth */
113 #define SG_g0_m_p_s2          9.80665   // m/s2
114 
115 /**standard pressure at SL */
116 #define SG_p0_Pa              101325.0 // Pa
117 
118 /**standard density at SL */
119 #define SG_rho0_kg_p_m3       1.225 // kg/m3
120 
121 /**standard temperature at SL */
122 #define SG_T0_K               288.15   // K (=15degC)
123 
124 /**specific gas constant of air*/
125 #define SG_R_m2_p_s2_p_K      287.05   // m2/s2/K
126 
127 /**specific heat constant at constant pressure*/
128 #define SG_cp_m2_p_s2_p_K 1004.68      // m2/s2/K
129 
130 /**ratio of specific heats of air*/
131 #define SG_gamma              1.4         // =cp/cv (cp = 1004.68 m2/s2 K , cv = 717.63 m2/s2 K)
132 
133 /**constant beta used to calculate dynamic viscosity */
134 #define SG_beta_kg_p_sm_sqrK  1.458e-06   // kg/s/m/SQRT(K)
135 
136 /** Sutherland constant */
137 #define SG_S_K                110.4       // K
138 
139 
140 // Conversions
141 
142 /** Arc seconds to radians.  (arcsec*pi)/(3600*180) = rad */
143 #define SG_ARCSEC_TO_RAD    4.84813681109535993589e-06
144 
145 /** Radians to arc seconds.  (rad*3600*180)/pi = arcsec */
146 #define SG_RAD_TO_ARCSEC    206264.806247096355156
147 
148 /** Feet to Meters */
149 #define SG_FEET_TO_METER    0.3048
150 
151 /** Meters to Feet */
152 #define SG_METER_TO_FEET    3.28083989501312335958
153 
154 /** Meters to Nautical Miles.  1 nm = 6076.11549 feet */
155 #define SG_METER_TO_NM      0.0005399568034557235
156 
157 /** Nautical Miles to Meters */
158 #define SG_NM_TO_METER      1852.0000
159 
160 /** Meters to Statute Miles. */
161 #define SG_METER_TO_SM      0.0006213699494949496
162 
163 /** Statute Miles to Meters. */
164 #define SG_SM_TO_METER      1609.3412196
165 
166 /** Radians to Nautical Miles.  1 nm = 1/60 of a degree */
167 #define SG_NM_TO_RAD        0.00029088820866572159
168 
169 /** Nautical Miles to Radians */
170 #define SG_RAD_TO_NM        3437.7467707849392526
171 
172 /** meters per second to Knots */
173 #define SG_MPS_TO_KT        1.9438444924406046432
174 
175 /** Knots to meters per second */
176 #define SG_KT_TO_MPS        0.5144444444444444444
177 
178 /** Feet per second to Knots */
179 #define SG_FPS_TO_KT        0.5924838012958962841
180 
181 /** Knots to Feet per second */
182 #define SG_KT_TO_FPS        1.6878098571011956874
183 
184 /** meters per second to Miles per hour */
185 #define SG_MPS_TO_MPH       2.2369362920544020312
186 
187 /** meetrs per hour to Miles per second */
188 #define SG_MPH_TO_MPS       0.44704
189 
190 /** Meters per second to Kilometers per hour */
191 #define SG_MPS_TO_KMH       3.6
192 
193 /** Kilometers per hour to meters per second */
194 #define SG_KMH_TO_MPS       0.2777777777777777778
195 
196 /** Pascal to Inch Mercury */
197 #define SG_PA_TO_INHG       0.0002952998330101010
198 
199 /** Inch Mercury to Pascal */
200 #define SG_INHG_TO_PA       3386.388640341
201 
202 /** slug/ft3 to kg/m3 */
203 #define SG_SLUGFT3_TO_KGPM3   515.379
204 
205 
206 /** For divide by zero avoidance, this will be close enough to zero */
207 #define SG_EPSILON 0.0000001
208 
209 /** Highest binobj format version we know how to read/write.  This starts at
210  *  0 and can go up to 65535 */
211 #define SG_BINOBJ_VERSION 6
212 
213 /** for backwards compatibility */
214 #define SG_SCENERY_FILE_FORMAT "0.4"
215 
216 /** Default object ranges.  Overridden by /sim/rendering/static-lod/[bare|rough|detailed] **/
217 #define SG_OBJECT_RANGE_BARE     30000.0
218 #define SG_OBJECT_RANGE_ROUGH     9000.0
219 #define SG_OBJECT_RANGE_DETAILED  1500.0
220 
221 /** Minimum expiry time of PagedLOD within the Tile.  Overridden by /sim/rendering/plod-minimum-expiry-time-secs **/
222 #define SG_TILE_MIN_EXPIRY 180.0
223 
224 /** Radius of scenery tiles in m **/
225 #define SG_TILE_RADIUS      14000.0
226 
227 #endif // _SG_CONSTANTS_H
228