# # Trigonometric functions, mostly inherited from Math::Complex. # -- Jarkko Hietaniemi, since April 1997 # -- Raphael Manfredi, September 1996 (indirectly: because of Math::Complex) # package Math::Trig; { use 5.006; } use strict; use Math::Complex 1.59; use Math::Complex qw(:trig :pi); require Exporter; our @ISA = qw(Exporter); our $VERSION = 1.23; my @angcnv = qw(rad2deg rad2grad deg2rad deg2grad grad2rad grad2deg); my @areal = qw(asin_real acos_real); our @EXPORT = (@{$Math::Complex::EXPORT_TAGS{'trig'}}, @angcnv, @areal); my @rdlcnv = qw(cartesian_to_cylindrical cartesian_to_spherical cylindrical_to_cartesian cylindrical_to_spherical spherical_to_cartesian spherical_to_cylindrical); my @greatcircle = qw( great_circle_distance great_circle_direction great_circle_bearing great_circle_waypoint great_circle_midpoint great_circle_destination ); my @pi = qw(pi pi2 pi4 pip2 pip4); our @EXPORT_OK = (@rdlcnv, @greatcircle, @pi, 'Inf'); # See e.g. the following pages: # http://www.movable-type.co.uk/scripts/LatLong.html # http://williams.best.vwh.net/avform.htm our %EXPORT_TAGS = ('radial' => [ @rdlcnv ], 'great_circle' => [ @greatcircle ], 'pi' => [ @pi ]); sub _DR () { pi2/360 } sub _RD () { 360/pi2 } sub _DG () { 400/360 } sub _GD () { 360/400 } sub _RG () { 400/pi2 } sub _GR () { pi2/400 } # # Truncating remainder. # sub _remt ($$) { # Oh yes, POSIX::fmod() would be faster. Possibly. If it is available. $_[0] - $_[1] * int($_[0] / $_[1]); } # # Angle conversions. # sub rad2rad($) { _remt($_[0], pi2) } sub deg2deg($) { _remt($_[0], 360) } sub grad2grad($) { _remt($_[0], 400) } sub rad2deg ($;$) { my $d = _RD * $_[0]; $_[1] ? $d : deg2deg($d) } sub deg2rad ($;$) { my $d = _DR * $_[0]; $_[1] ? $d : rad2rad($d) } sub grad2deg ($;$) { my $d = _GD * $_[0]; $_[1] ? $d : deg2deg($d) } sub deg2grad ($;$) { my $d = _DG * $_[0]; $_[1] ? $d : grad2grad($d) } sub rad2grad ($;$) { my $d = _RG * $_[0]; $_[1] ? $d : grad2grad($d) } sub grad2rad ($;$) { my $d = _GR * $_[0]; $_[1] ? $d : rad2rad($d) } # # acos and asin functions which always return a real number # sub acos_real { return 0 if $_[0] >= 1; return pi if $_[0] <= -1; return acos($_[0]); } sub asin_real { return &pip2 if $_[0] >= 1; return -&pip2 if $_[0] <= -1; return asin($_[0]); } sub cartesian_to_spherical { my ( $x, $y, $z ) = @_; my $rho = sqrt( $x * $x + $y * $y + $z * $z ); return ( $rho, atan2( $y, $x ), $rho ? acos_real( $z / $rho ) : 0 ); } sub spherical_to_cartesian { my ( $rho, $theta, $phi ) = @_; return ( $rho * cos( $theta ) * sin( $phi ), $rho * sin( $theta ) * sin( $phi ), $rho * cos( $phi ) ); } sub spherical_to_cylindrical { my ( $x, $y, $z ) = spherical_to_cartesian( @_ ); return ( sqrt( $x * $x + $y * $y ), $_[1], $z ); } sub cartesian_to_cylindrical { my ( $x, $y, $z ) = @_; return ( sqrt( $x * $x + $y * $y ), atan2( $y, $x ), $z ); } sub cylindrical_to_cartesian { my ( $rho, $theta, $z ) = @_; return ( $rho * cos( $theta ), $rho * sin( $theta ), $z ); } sub cylindrical_to_spherical { return ( cartesian_to_spherical( cylindrical_to_cartesian( @_ ) ) ); } sub great_circle_distance { my ( $theta0, $phi0, $theta1, $phi1, $rho ) = @_; $rho = 1 unless defined $rho; # Default to the unit sphere. my $lat0 = pip2 - $phi0; my $lat1 = pip2 - $phi1; return $rho * acos_real( cos( $lat0 ) * cos( $lat1 ) * cos( $theta0 - $theta1 ) + sin( $lat0 ) * sin( $lat1 ) ); } sub great_circle_direction { my ( $theta0, $phi0, $theta1, $phi1 ) = @_; my $lat0 = pip2 - $phi0; my $lat1 = pip2 - $phi1; return rad2rad(pi2 - atan2(sin($theta0-$theta1) * cos($lat1), cos($lat0) * sin($lat1) - sin($lat0) * cos($lat1) * cos($theta0-$theta1))); } *great_circle_bearing = \&great_circle_direction; sub great_circle_waypoint { my ( $theta0, $phi0, $theta1, $phi1, $point ) = @_; $point = 0.5 unless defined $point; my $d = great_circle_distance( $theta0, $phi0, $theta1, $phi1 ); return undef if $d == pi; my $sd = sin($d); return ($theta0, $phi0) if $sd == 0; my $A = sin((1 - $point) * $d) / $sd; my $B = sin( $point * $d) / $sd; my $lat0 = pip2 - $phi0; my $lat1 = pip2 - $phi1; my $x = $A * cos($lat0) * cos($theta0) + $B * cos($lat1) * cos($theta1); my $y = $A * cos($lat0) * sin($theta0) + $B * cos($lat1) * sin($theta1); my $z = $A * sin($lat0) + $B * sin($lat1); my $theta = atan2($y, $x); my $phi = acos_real($z); return ($theta, $phi); } sub great_circle_midpoint { great_circle_waypoint(@_[0..3], 0.5); } sub great_circle_destination { my ( $theta0, $phi0, $dir0, $dst ) = @_; my $lat0 = pip2 - $phi0; my $phi1 = asin_real(sin($lat0)*cos($dst) + cos($lat0)*sin($dst)*cos($dir0)); my $theta1 = $theta0 + atan2(sin($dir0)*sin($dst)*cos($lat0), cos($dst)-sin($lat0)*sin($phi1)); my $dir1 = great_circle_bearing($theta1, $phi1, $theta0, $phi0) + pi; $dir1 -= pi2 if $dir1 > pi2; return ($theta1, $phi1, $dir1); } 1; __END__ =pod =head1 NAME Math::Trig - trigonometric functions =head1 SYNOPSIS use Math::Trig; $x = tan(0.9); $y = acos(3.7); $z = asin(2.4); $halfpi = pi/2; $rad = deg2rad(120); # Import constants pi2, pip2, pip4 (2*pi, pi/2, pi/4). use Math::Trig ':pi'; # Import the conversions between cartesian/spherical/cylindrical. use Math::Trig ':radial'; # Import the great circle formulas. use Math::Trig ':great_circle'; =head1 DESCRIPTION C<Math::Trig> defines many trigonometric functions not defined by the core Perl which defines only the C<sin()> and C<cos()>. The constant B<pi> is also defined as are a few convenience functions for angle conversions, and I<great circle formulas> for spherical movement. =head1 TRIGONOMETRIC FUNCTIONS The tangent =over 4 =item B<tan> =back The cofunctions of the sine, cosine, and tangent (cosec/csc and cotan/cot are aliases) B<csc>, B<cosec>, B<sec>, B<sec>, B<cot>, B<cotan> The arcus (also known as the inverse) functions of the sine, cosine, and tangent B<asin>, B<acos>, B<atan> The principal value of the arc tangent of y/x B<atan2>(y, x) The arcus cofunctions of the sine, cosine, and tangent (acosec/acsc and acotan/acot are aliases). Note that atan2(0, 0) is not well-defined. B<acsc>, B<acosec>, B<asec>, B<acot>, B<acotan> The hyperbolic sine, cosine, and tangent B<sinh>, B<cosh>, B<tanh> The cofunctions of the hyperbolic sine, cosine, and tangent (cosech/csch and cotanh/coth are aliases) B<csch>, B<cosech>, B<sech>, B<coth>, B<cotanh> The area (also known as the inverse) functions of the hyperbolic sine, cosine, and tangent B<asinh>, B<acosh>, B<atanh> The area cofunctions of the hyperbolic sine, cosine, and tangent (acsch/acosech and acoth/acotanh are aliases) B<acsch>, B<acosech>, B<asech>, B<acoth>, B<acotanh> The trigonometric constant B<pi> and some of handy multiples of it are also defined. B<pi, pi2, pi4, pip2, pip4> =head2 ERRORS DUE TO DIVISION BY ZERO The following functions acoth acsc acsch asec asech atanh cot coth csc csch sec sech tan tanh cannot be computed for all arguments because that would mean dividing by zero or taking logarithm of zero. These situations cause fatal runtime errors looking like this cot(0): Division by zero. (Because in the definition of cot(0), the divisor sin(0) is 0) Died at ... or atanh(-1): Logarithm of zero. Died at... For the C<csc>, C<cot>, C<asec>, C<acsc>, C<acot>, C<csch>, C<coth>, C<asech>, C<acsch>, the argument cannot be C<0> (zero). For the C<atanh>, C<acoth>, the argument cannot be C<1> (one). For the C<atanh>, C<acoth>, the argument cannot be C<-1> (minus one). For the C<tan>, C<sec>, C<tanh>, C<sech>, the argument cannot be I<pi/2 + k * pi>, where I<k> is any integer. Note that atan2(0, 0) is not well-defined. =head2 SIMPLE (REAL) ARGUMENTS, COMPLEX RESULTS Please note that some of the trigonometric functions can break out from the B<real axis> into the B<complex plane>. For example C<asin(2)> has no definition for plain real numbers but it has definition for complex numbers. In Perl terms this means that supplying the usual Perl numbers (also known as scalars, please see L<perldata>) as input for the trigonometric functions might produce as output results that no more are simple real numbers: instead they are complex numbers. The C<Math::Trig> handles this by using the C<Math::Complex> package which knows how to handle complex numbers, please see L<Math::Complex> for more information. In practice you need not to worry about getting complex numbers as results because the C<Math::Complex> takes care of details like for example how to display complex numbers. For example: print asin(2), "\n"; should produce something like this (take or leave few last decimals): 1.5707963267949-1.31695789692482i That is, a complex number with the real part of approximately C<1.571> and the imaginary part of approximately C<-1.317>. =head1 PLANE ANGLE CONVERSIONS (Plane, 2-dimensional) angles may be converted with the following functions. =over =item deg2rad $radians = deg2rad($degrees); =item grad2rad $radians = grad2rad($gradians); =item rad2deg $degrees = rad2deg($radians); =item grad2deg $degrees = grad2deg($gradians); =item deg2grad $gradians = deg2grad($degrees); =item rad2grad $gradians = rad2grad($radians); =back The full circle is 2 I<pi> radians or I<360> degrees or I<400> gradians. The result is by default wrapped to be inside the [0, {2pi,360,400}[ circle. If you don't want this, supply a true second argument: $zillions_of_radians = deg2rad($zillions_of_degrees, 1); $negative_degrees = rad2deg($negative_radians, 1); You can also do the wrapping explicitly by rad2rad(), deg2deg(), and grad2grad(). =over 4 =item rad2rad $radians_wrapped_by_2pi = rad2rad($radians); =item deg2deg $degrees_wrapped_by_360 = deg2deg($degrees); =item grad2grad $gradians_wrapped_by_400 = grad2grad($gradians); =back =head1 RADIAL COORDINATE CONVERSIONS B<Radial coordinate systems> are the B<spherical> and the B<cylindrical> systems, explained shortly in more detail. You can import radial coordinate conversion functions by using the C<:radial> tag: use Math::Trig ':radial'; ($rho, $theta, $z) = cartesian_to_cylindrical($x, $y, $z); ($rho, $theta, $phi) = cartesian_to_spherical($x, $y, $z); ($x, $y, $z) = cylindrical_to_cartesian($rho, $theta, $z); ($rho_s, $theta, $phi) = cylindrical_to_spherical($rho_c, $theta, $z); ($x, $y, $z) = spherical_to_cartesian($rho, $theta, $phi); ($rho_c, $theta, $z) = spherical_to_cylindrical($rho_s, $theta, $phi); B<All angles are in radians>. =head2 COORDINATE SYSTEMS B<Cartesian> coordinates are the usual rectangular I<(x, y, z)>-coordinates. Spherical coordinates, I<(rho, theta, pi)>, are three-dimensional coordinates which define a point in three-dimensional space. They are based on a sphere surface. The radius of the sphere is B<rho>, also known as the I<radial> coordinate. The angle in the I<xy>-plane (around the I<z>-axis) is B<theta>, also known as the I<azimuthal> coordinate. The angle from the I<z>-axis is B<phi>, also known as the I<polar> coordinate. The North Pole is therefore I<0, 0, rho>, and the Gulf of Guinea (think of the missing big chunk of Africa) I<0, pi/2, rho>. In geographical terms I<phi> is latitude (northward positive, southward negative) and I<theta> is longitude (eastward positive, westward negative). B<BEWARE>: some texts define I<theta> and I<phi> the other way round, some texts define the I<phi> to start from the horizontal plane, some texts use I<r> in place of I<rho>. Cylindrical coordinates, I<(rho, theta, z)>, are three-dimensional coordinates which define a point in three-dimensional space. They are based on a cylinder surface. The radius of the cylinder is B<rho>, also known as the I<radial> coordinate. The angle in the I<xy>-plane (around the I<z>-axis) is B<theta>, also known as the I<azimuthal> coordinate. The third coordinate is the I<z>, pointing up from the B<theta>-plane. =head2 3-D ANGLE CONVERSIONS Conversions to and from spherical and cylindrical coordinates are available. Please notice that the conversions are not necessarily reversible because of the equalities like I<pi> angles being equal to I<-pi> angles. =over 4 =item cartesian_to_cylindrical ($rho, $theta, $z) = cartesian_to_cylindrical($x, $y, $z); =item cartesian_to_spherical ($rho, $theta, $phi) = cartesian_to_spherical($x, $y, $z); =item cylindrical_to_cartesian ($x, $y, $z) = cylindrical_to_cartesian($rho, $theta, $z); =item cylindrical_to_spherical ($rho_s, $theta, $phi) = cylindrical_to_spherical($rho_c, $theta, $z); Notice that when C<$z> is not 0 C<$rho_s> is not equal to C<$rho_c>. =item spherical_to_cartesian ($x, $y, $z) = spherical_to_cartesian($rho, $theta, $phi); =item spherical_to_cylindrical ($rho_c, $theta, $z) = spherical_to_cylindrical($rho_s, $theta, $phi); Notice that when C<$z> is not 0 C<$rho_c> is not equal to C<$rho_s>. =back =head1 GREAT CIRCLE DISTANCES AND DIRECTIONS A great circle is section of a circle that contains the circle diameter: the shortest distance between two (non-antipodal) points on the spherical surface goes along the great circle connecting those two points. =head2 great_circle_distance You can compute spherical distances, called B<great circle distances>, by importing the great_circle_distance() function: use Math::Trig 'great_circle_distance'; $distance = great_circle_distance($theta0, $phi0, $theta1, $phi1, [, $rho]); The I<great circle distance> is the shortest distance between two points on a sphere. The distance is in C<$rho> units. The C<$rho> is optional, it defaults to 1 (the unit sphere), therefore the distance defaults to radians. If you think geographically the I<theta> are longitudes: zero at the Greenwhich meridian, eastward positive, westward negative -- and the I<phi> are latitudes: zero at the North Pole, northward positive, southward negative. B<NOTE>: this formula thinks in mathematics, not geographically: the I<phi> zero is at the North Pole, not at the Equator on the west coast of Africa (Bay of Guinea). You need to subtract your geographical coordinates from I<pi/2> (also known as 90 degrees). $distance = great_circle_distance($lon0, pi/2 - $lat0, $lon1, pi/2 - $lat1, $rho); =head2 great_circle_direction The direction you must follow the great circle (also known as I<bearing>) can be computed by the great_circle_direction() function: use Math::Trig 'great_circle_direction'; $direction = great_circle_direction($theta0, $phi0, $theta1, $phi1); =head2 great_circle_bearing Alias 'great_circle_bearing' for 'great_circle_direction' is also available. use Math::Trig 'great_circle_bearing'; $direction = great_circle_bearing($theta0, $phi0, $theta1, $phi1); The result of great_circle_direction is in radians, zero indicating straight north, pi or -pi straight south, pi/2 straight west, and -pi/2 straight east. =head2 great_circle_destination You can inversely compute the destination if you know the starting point, direction, and distance: use Math::Trig 'great_circle_destination'; # $diro is the original direction, # for example from great_circle_bearing(). # $distance is the angular distance in radians, # for example from great_circle_distance(). # $thetad and $phid are the destination coordinates, # $dird is the final direction at the destination. ($thetad, $phid, $dird) = great_circle_destination($theta, $phi, $diro, $distance); or the midpoint if you know the end points: =head2 great_circle_midpoint use Math::Trig 'great_circle_midpoint'; ($thetam, $phim) = great_circle_midpoint($theta0, $phi0, $theta1, $phi1); The great_circle_midpoint() is just a special case of =head2 great_circle_waypoint use Math::Trig 'great_circle_waypoint'; ($thetai, $phii) = great_circle_waypoint($theta0, $phi0, $theta1, $phi1, $way); Where the $way is a value from zero ($theta0, $phi0) to one ($theta1, $phi1). Note that antipodal points (where their distance is I<pi> radians) do not have waypoints between them (they would have an an "equator" between them), and therefore C<undef> is returned for antipodal points. If the points are the same and the distance therefore zero and all waypoints therefore identical, the first point (either point) is returned. The thetas, phis, direction, and distance in the above are all in radians. You can import all the great circle formulas by use Math::Trig ':great_circle'; Notice that the resulting directions might be somewhat surprising if you are looking at a flat worldmap: in such map projections the great circles quite often do not look like the shortest routes -- but for example the shortest possible routes from Europe or North America to Asia do often cross the polar regions. (The common Mercator projection does B<not> show great circles as straight lines: straight lines in the Mercator projection are lines of constant bearing.) =head1 EXAMPLES To calculate the distance between London (51.3N 0.5W) and Tokyo (35.7N 139.8E) in kilometers: use Math::Trig qw(great_circle_distance deg2rad); # Notice the 90 - latitude: phi zero is at the North Pole. sub NESW { deg2rad($_[0]), deg2rad(90 - $_[1]) } my @L = NESW( -0.5, 51.3); my @T = NESW(139.8, 35.7); my $km = great_circle_distance(@L, @T, 6378); # About 9600 km. The direction you would have to go from London to Tokyo (in radians, straight north being zero, straight east being pi/2). use Math::Trig qw(great_circle_direction); my $rad = great_circle_direction(@L, @T); # About 0.547 or 0.174 pi. The midpoint between London and Tokyo being use Math::Trig qw(great_circle_midpoint); my @M = great_circle_midpoint(@L, @T); or about 69 N 89 E, in the frozen wastes of Siberia. B<NOTE>: you B<cannot> get from A to B like this: Dist = great_circle_distance(A, B) Dir = great_circle_direction(A, B) C = great_circle_destination(A, Dist, Dir) and expect C to be B, because the bearing constantly changes when going from A to B (except in some special case like the meridians or the circles of latitudes) and in great_circle_destination() one gives a B<constant> bearing to follow. =head2 CAVEAT FOR GREAT CIRCLE FORMULAS The answers may be off by few percentages because of the irregular (slightly aspherical) form of the Earth. The errors are at worst about 0.55%, but generally below 0.3%. =head2 Real-valued asin and acos For small inputs asin() and acos() may return complex numbers even when real numbers would be enough and correct, this happens because of floating-point inaccuracies. You can see these inaccuracies for example by trying theses: print cos(1e-6)**2+sin(1e-6)**2 - 1,"\n"; printf "%.20f", cos(1e-6)**2+sin(1e-6)**2,"\n"; which will print something like this -1.11022302462516e-16 0.99999999999999988898 even though the expected results are of course exactly zero and one. The formulas used to compute asin() and acos() are quite sensitive to this, and therefore they might accidentally slip into the complex plane even when they should not. To counter this there are two interfaces that are guaranteed to return a real-valued output. =over 4 =item asin_real use Math::Trig qw(asin_real); $real_angle = asin_real($input_sin); Return a real-valued arcus sine if the input is between [-1, 1], B<inclusive> the endpoints. For inputs greater than one, pi/2 is returned. For inputs less than minus one, -pi/2 is returned. =item acos_real use Math::Trig qw(acos_real); $real_angle = acos_real($input_cos); Return a real-valued arcus cosine if the input is between [-1, 1], B<inclusive> the endpoints. For inputs greater than one, zero is returned. For inputs less than minus one, pi is returned. =back =head1 BUGS Saying C<use Math::Trig;> exports many mathematical routines in the caller environment and even overrides some (C<sin>, C<cos>). This is construed as a feature by the Authors, actually... ;-) The code is not optimized for speed, especially because we use C<Math::Complex> and thus go quite near complex numbers while doing the computations even when the arguments are not. This, however, cannot be completely avoided if we want things like C<asin(2)> to give an answer instead of giving a fatal runtime error. Do not attempt navigation using these formulas. L<Math::Complex> =head1 AUTHORS Jarkko Hietaniemi <F<jhi!at!iki.fi>>, Raphael Manfredi <F<Raphael_Manfredi!at!pobox.com>>, Zefram <zefram@fysh.org> =head1 LICENSE This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. =cut # eof SIMPAN PERUBAHAN