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LSST Data Management Base Package
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constants.h
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1/*
2 * This file is part of sphgeom.
3 *
4 * Developed for the LSST Data Management System.
5 * This product includes software developed by the LSST Project
6 * (http://www.lsst.org).
7 * See the COPYRIGHT file at the top-level directory of this distribution
8 * for details of code ownership.
9 *
10 * This software is dual licensed under the GNU General Public License and also
11 * under a 3-clause BSD license. Recipients may choose which of these licenses
12 * to use; please see the files gpl-3.0.txt and/or bsd_license.txt,
13 * respectively. If you choose the GPL option then the following text applies
14 * (but note that there is still no warranty even if you opt for BSD instead):
15 *
16 * This program is free software: you can redistribute it and/or modify
17 * it under the terms of the GNU General Public License as published by
18 * the Free Software Foundation, either version 3 of the License, or
19 * (at your option) any later version.
20 *
21 * This program is distributed in the hope that it will be useful,
22 * but WITHOUT ANY WARRANTY; without even the implied warranty of
23 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
24 * GNU General Public License for more details.
25 *
26 * You should have received a copy of the GNU General Public License
27 * along with this program. If not, see <http://www.gnu.org/licenses/>.
28 */
29
30#ifndef LSST_SPHGEOM_CONSTANTS_H_
31#define LSST_SPHGEOM_CONSTANTS_H_
32
35
36
37namespace lsst {
38namespace sphgeom {
39
40// Note: given a compiler that does correctly rounded decimal to
41// binary floating point conversions, PI = 0x1.921fb54442d18p1 in
42// IEEE double precision format. This is less than π.
43constexpr double PI = 3.1415926535897932384626433832795;
44constexpr double ONE_OVER_PI = 0.318309886183790671537767526745;
45constexpr double RAD_PER_DEG = 0.0174532925199432957692369076849;
46constexpr double DEG_PER_RAD = 57.2957795130823208767981548141;
47
48// The maximum error of std::asin in IEEE double precision arithmetic,
49// assuming 1 ulp of error in its argument, is about
50// π/2 - arcsin (1 - 2⁻⁵³), or a little less than 1.5e-8 radians
51// (3.1 milliarcsec).
52constexpr double MAX_ASIN_ERROR = 1.5e-8;
53
54// The computation of squared chord length between two unit vectors
55// involves 8 elementary operations on numbers with magnitude ≤ 4. Its
56// maximum error can be shown to be < 2.5e-15.
57constexpr double MAX_SQUARED_CHORD_LENGTH_ERROR = 2.5e-15;
58
59// The largest value ε such that 1 + ε rounds to 1 in IEEE double
60// precision, assuming round-to-nearest-ties-to-even rounding.
61constexpr double EPSILON = 1.1102230246251565e-16;
62
63}} // namespace lsst::sphgeom
64
65#endif // LSST_SPHGEOM_CONSTANTS_H_
constexpr double MAX_ASIN_ERROR
Definition constants.h:52
constexpr double DEG_PER_RAD
Definition constants.h:46
constexpr double MAX_SQUARED_CHORD_LENGTH_ERROR
Definition constants.h:57
constexpr double ONE_OVER_PI
Definition constants.h:44
constexpr double RAD_PER_DEG
Definition constants.h:45
constexpr double EPSILON
Definition constants.h:61
constexpr double PI
Definition constants.h:43