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trigonometry.scad
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trigonometry.scad
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//////////////////////////////////////////////////////////////////////
// LibFile: trigonometry.scad
// Trigonometry shortcuts for people who can't be bothered to remember
// all the function relations, or silly acronyms like SOHCAHTOA.
// Includes:
// include <BOSL2/std.scad>
// FileGroup: Math
// FileSummary: Trigonometry shortcuts for when you can't recall the mnemonic SOHCAHTOA.
// FileFootnotes: STD=Included in std.scad
//////////////////////////////////////////////////////////////////////
// Section: 2D General Triangle Functions
// Function: law_of_cosines()
// Usage:
// C = law_of_cosines(a, b, c);
// c = law_of_cosines(a, b, C=);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Applies the Law of Cosines for an arbitrary triangle. Given three side lengths, returns the
// angle in degrees for the corner opposite of the third side. Given two side lengths, and the
// angle between them, returns the length of the third side.
// Figure(2D):
// stroke([[-50,0], [10,60], [50,0]], closed=true);
// color("black") {
// translate([ 33,35]) text(text="a", size=8, halign="center", valign="center");
// translate([ 0,-6]) text(text="b", size=8, halign="center", valign="center");
// translate([-22,35]) text(text="c", size=8, halign="center", valign="center");
// }
// color("blue") {
// translate([-37, 6]) text(text="A", size=8, halign="center", valign="center");
// translate([ 9,51]) text(text="B", size=8, halign="center", valign="center");
// translate([ 38, 6]) text(text="C", size=8, halign="center", valign="center");
// }
// Arguments:
// a = The length of the first side.
// b = The length of the second side.
// c = The length of the third side.
// ---
// C = The angle in degrees of the corner opposite of the third side.
// See Also: law_of_sines()
function law_of_cosines(a, b, c, C) =
// Triangle Law of Cosines:
// c^2 = a^2 + b^2 - 2*a*b*cos(C)
assert(num_defined([c,C]) == 1, "Must give exactly one of c= or C=.")
is_undef(c) ? sqrt(a*a + b*b - 2*a*b*cos(C)) :
acos(constrain((a*a + b*b - c*c) / (2*a*b), -1, 1));
// Function: law_of_sines()
// Usage:
// B = law_of_sines(a, A, b);
// b = law_of_sines(a, A, B=);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Applies the Law of Sines for an arbitrary triangle. Given two triangle side lengths and the
// angle between them, returns the angle of the corner opposite of the second side. Given a side
// length, the opposing angle, and a second angle, returns the length of the side opposite of the
// second angle.
// Figure(2D):
// stroke([[-50,0], [10,60], [50,0]], closed=true);
// color("black") {
// translate([ 33,35]) text(text="a", size=8, halign="center", valign="center");
// translate([ 0,-6]) text(text="b", size=8, halign="center", valign="center");
// translate([-22,35]) text(text="c", size=8, halign="center", valign="center");
// }
// color("blue") {
// translate([-37, 6]) text(text="A", size=8, halign="center", valign="center");
// translate([ 9,51]) text(text="B", size=8, halign="center", valign="center");
// translate([ 38, 6]) text(text="C", size=8, halign="center", valign="center");
// }
// Arguments:
// a = The length of the first side.
// A = The angle in degrees of the corner opposite of the first side.
// b = The length of the second side.
// ---
// B = The angle in degrees of the corner opposite of the second side.
// See Also: law_of_cosines()
function law_of_sines(a, A, b, B) =
// Triangle Law of Sines:
// a/sin(A) = b/sin(B) = c/sin(C)
assert(num_defined([b,B]) == 1, "Must give exactly one of b= or B=.")
let( r = a/sin(A) )
is_undef(b) ? r*sin(B) :
asin(constrain(b/r, -1, 1));
// Section: 2D Right Triangle Functions
// This is a set of functions to make it easier to perform trig calculations on right triangles.
// In general, all these functions are named using these abbreviations:
// - **hyp**: The length of the Hypotenuse.
// - **adj**: The length of the side adjacent to the angle.
// - **opp**: The length of the side opposite to the angle.
// - **ang**: The angle size in degrees.
// .
// If you know two of those, and want to know the value of a third, you will need to call a
// function named like `AAA_BBB_to_CCC()`. For example, if you know the length of the hypotenuse,
// and the length of the side adjacent to the angle, and want to learn the length of the side
// opposite to the angle, you will call `opp = hyp_adj_to_opp(hyp,adj);`.
// Figure(2D):
// color("brown") {
// stroke([[40,0], [40,10], [50,10]]);
// left(50) stroke(arc(r=37,angle=30));
// }
// color("lightgreen") stroke([[-50,0], [50,60], [50,0]], closed=true);
// color("black") {
// translate([ 62,25]) text(text="opp", size=8, halign="center", valign="center");
// translate([ 0,-6]) text(text="adj", size=8, halign="center", valign="center");
// translate([ 0,40]) text(text="hyp", size=8, halign="center", valign="center");
// translate([-25, 5]) text(text="ang", size=7, halign="center", valign="center");
// }
// Function: hyp_opp_to_adj()
// Alias: opp_hyp_to_adj()
// Usage:
// adj = hyp_opp_to_adj(hyp,opp);
// adj = opp_hyp_to_adj(opp,hyp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the lengths of the hypotenuse and opposite side of a right triangle, returns the length
// of the adjacent side.
// Arguments:
// hyp = The length of the hypotenuse of the right triangle.
// opp = The length of the side of the right triangle that is opposite from the primary angle.
// Example:
// hyp = hyp_opp_to_adj(5,3); // Returns: 4
function hyp_opp_to_adj(hyp,opp) =
assert(is_finite(hyp+opp) && hyp>=0 && opp>=0,
"Triangle side lengths should be a positive numbers." )
sqrt(hyp*hyp-opp*opp);
function opp_hyp_to_adj(opp,hyp) = hyp_opp_to_adj(hyp,opp);
// Function: hyp_ang_to_adj()
// Alias: ang_hyp_to_adj()
// Usage:
// adj = hyp_ang_to_adj(hyp,ang);
// adj = ang_hyp_to_adj(ang,hyp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the length of the hypotenuse and the angle of the primary corner of a right triangle,
// returns the length of the adjacent side.
// Arguments:
// hyp = The length of the hypotenuse of the right triangle.
// ang = The angle in degrees of the primary corner of the right triangle.
// Example:
// adj = hyp_ang_to_adj(8,60); // Returns: 4
function hyp_ang_to_adj(hyp,ang) =
assert(is_finite(hyp) && hyp>=0, "Triangle side length should be a positive number." )
assert(is_finite(ang) && ang>-90 && ang<90, "The angle should be an acute angle." )
hyp*cos(ang);
function ang_hyp_to_adj(ang,hyp) = hyp_ang_to_adj(hyp, ang);
// Function: opp_ang_to_adj()
// Alias: ang_opp_to_adj()
// Usage:
// adj = opp_ang_to_adj(opp,ang);
// adj = ang_opp_to_adj(ang,opp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the angle of the primary corner of a right triangle, and the length of the side opposite of it,
// returns the length of the adjacent side.
// Arguments:
// opp = The length of the side of the right triangle that is opposite from the primary angle.
// ang = The angle in degrees of the primary corner of the right triangle.
// Example:
// adj = opp_ang_to_adj(8,30); // Returns: 4
function opp_ang_to_adj(opp,ang) =
assert(is_finite(opp) && opp>=0, "Triangle side length should be a positive number." )
assert(is_finite(ang) && ang>-90 && ang<90, "The angle should be an acute angle." )
opp/tan(ang);
function ang_opp_to_adj(ang,opp) = opp_ang_to_adj(opp,ang);
// Function: hyp_adj_to_opp()
// Alias: adj_hyp_to_opp()
// Usage:
// opp = hyp_adj_to_opp(hyp,adj);
// opp = adj_hyp_to_opp(adj,hyp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the length of the hypotenuse and the adjacent side, returns the length of the opposite side.
// Arguments:
// hyp = The length of the hypotenuse of the right triangle.
// adj = The length of the side of the right triangle that is adjacent to the primary angle.
// Example:
// opp = hyp_adj_to_opp(5,4); // Returns: 3
function hyp_adj_to_opp(hyp,adj) =
assert(is_finite(hyp) && hyp>=0 && is_finite(adj) && adj>=0,
"Triangle side lengths should be a positive numbers." )
sqrt(hyp*hyp-adj*adj);
function adj_hyp_to_opp(adj,hyp) = hyp_adj_to_opp(hyp,adj);
// Function: hyp_ang_to_opp()
// Alias: ang_hyp_to_opp()
// Usage:
// opp = hyp_ang_to_opp(hyp,ang);
// opp = ang_hyp_to_opp(ang,hyp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the length of the hypotenuse of a right triangle, and the angle of the corner, returns the length of the opposite side.
// Arguments:
// hyp = The length of the hypotenuse of the right triangle.
// ang = The angle in degrees of the primary corner of the right triangle.
// Example:
// opp = hyp_ang_to_opp(8,30); // Returns: 4
function hyp_ang_to_opp(hyp,ang) =
assert(is_finite(hyp)&&hyp>=0, "Triangle side length should be a positive number." )
assert(is_finite(ang) && ang>-90 && ang<90, "The angle should be an acute angle." )
hyp*sin(ang);
function ang_hyp_to_opp(ang,hyp) = hyp_ang_to_opp(hyp,ang);
// Function: adj_ang_to_opp()
// Alias: ang_adj_to_opp()
// Usage:
// opp = adj_ang_to_opp(adj,ang);
// opp = ang_adj_to_opp(ang,adj);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the length of the adjacent side of a right triangle, and the angle of the corner, returns the length of the opposite side.
// Arguments:
// adj = The length of the side of the right triangle that is adjacent to the primary angle.
// ang = The angle in degrees of the primary corner of the right triangle.
// Example:
// opp = adj_ang_to_opp(8,45); // Returns: 8
function adj_ang_to_opp(adj,ang) =
assert(is_finite(adj)&&adj>=0, "Triangle side length should be a positive number." )
assert(is_finite(ang) && ang>-90 && ang<90, "The angle should be an acute angle." )
adj*tan(ang);
function ang_adj_to_opp(ang,adj) = adj_ang_to_opp(adj,ang);
// Function: adj_opp_to_hyp()
// Alias: opp_adj_to_hyp()
// Usage:
// hyp = adj_opp_to_hyp(adj,opp);
// hyp = opp_adj_to_hyp(opp,adj);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// Given the length of the adjacent and opposite sides of a right triangle, returns the length of thee hypotenuse.
// Arguments:
// adj = The length of the side of the right triangle that is adjacent to the primary angle.
// opp = The length of the side of the right triangle that is opposite from the primary angle.
// Example:
// hyp = adj_opp_to_hyp(3,4); // Returns: 5
function adj_opp_to_hyp(adj,opp) =
assert(is_finite(opp) && opp>=0 && is_finite(adj) && adj>=0,
"Triangle side lengths should be a positive numbers." )
norm([opp,adj]);
function opp_adj_to_hyp(opp,adj) = adj_opp_to_hyp(adj,opp);
// Function: adj_ang_to_hyp()
// Alias: ang_adj_to_hyp()
// Usage:
// hyp = adj_ang_to_hyp(adj,ang);
// hyp = ang_adj_to_hyp(ang,adj);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// For a right triangle, given the length of the adjacent side, and the corner angle, returns the length of the hypotenuse.
// Arguments:
// adj = The length of the side of the right triangle that is adjacent to the primary angle.
// ang = The angle in degrees of the primary corner of the right triangle.
// Example:
// hyp = adj_ang_to_hyp(4,60); // Returns: 8
function adj_ang_to_hyp(adj,ang) =
assert(is_finite(adj) && adj>=0, "Triangle side length should be a positive number." )
assert(is_finite(ang) && ang>-90 && ang<90, "The angle should be an acute angle." )
adj/cos(ang);
function ang_adj_to_hyp(ang,adj) = adj_ang_to_hyp(adj,ang);
// Function: opp_ang_to_hyp()
// Alias: ang_opp_to_hyp()
// Usage:
// hyp = opp_ang_to_hyp(opp,ang);
// hyp = ang_opp_to_hyp(ang,opp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// For a right triangle, given the length of the opposite side, and the corner angle, returns the length of the hypotenuse.
// Arguments:
// opp = The length of the side of the right triangle that is opposite from the primary angle.
// ang = The angle in degrees of the primary corner of the right triangle.
// Example:
// hyp = opp_ang_to_hyp(4,30); // Returns: 8
function opp_ang_to_hyp(opp,ang) =
assert(is_finite(opp) && opp>=0, "Triangle side length should be a positive number." )
assert(is_finite(ang) && ang>-90 && ang<90, "The angle should be an acute angle." )
opp/sin(ang);
function ang_opp_to_hyp(ang,opp) = opp_ang_to_hyp(opp,ang);
// Function: hyp_adj_to_ang()
// Alias: adj_hyp_to_ang()
// Usage:
// ang = hyp_adj_to_ang(hyp,adj);
// ang = adj_hyp_to_ang(adj,hyp);
// Description:
// For a right triangle, given the lengths of the hypotenuse and the adjacent sides, returns the angle of the corner.
// Arguments:
// hyp = The length of the hypotenuse of the right triangle.
// adj = The length of the side of the right triangle that is adjacent to the primary angle.
// Example:
// ang = hyp_adj_to_ang(8,4); // Returns: 60 degrees
function hyp_adj_to_ang(hyp,adj) =
assert(is_finite(hyp) && hyp>0 && is_finite(adj) && adj>=0,
"Triangle side lengths should be positive numbers." )
acos(adj/hyp);
function adj_hyp_to_ang(adj,hyp) = hyp_adj_to_ang(hyp,adj);
// Function: hyp_opp_to_ang()
// Alias: opp_hyp_to_ang()
// Usage:
// ang = hyp_opp_to_ang(hyp,opp);
// ang = opp_hyp_to_ang(opp,hyp);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// For a right triangle, given the lengths of the hypotenuse and the opposite sides, returns the angle of the corner.
// Arguments:
// hyp = The length of the hypotenuse of the right triangle.
// opp = The length of the side of the right triangle that is opposite from the primary angle.
// Example:
// ang = hyp_opp_to_ang(8,4); // Returns: 30 degrees
function hyp_opp_to_ang(hyp,opp) =
assert(is_finite(hyp+opp) && hyp>0 && opp>=0,
"Triangle side lengths should be positive numbers." )
asin(opp/hyp);
function opp_hyp_to_ang(opp,hyp) = hyp_opp_to_ang(hyp,opp);
// Function: adj_opp_to_ang()
// Alias: opp_adj_to_ang()
// Usage:
// ang = adj_opp_to_ang(adj,opp);
// ang = opp_adj_to_ang(opp,adj);
// Topics: Geometry, Trigonometry, Triangles
// Description:
// For a right triangle, given the lengths of the adjacent and opposite sides, returns the angle of the corner.
// Arguments:
// adj = The length of the side of the right triangle that is adjacent to the primary angle.
// opp = The length of the side of the right triangle that is opposite from the primary angle.
// Example:
// ang = adj_opp_to_ang(sqrt(3)/2,0.5); // Returns: 30 degrees
function adj_opp_to_ang(adj,opp) =
assert(is_finite(adj+opp) && adj>0 && opp>=0,
"Triangle side lengths should be positive numbers." )
atan2(opp,adj);
function opp_adj_to_ang(opp,adj) = adj_opp_to_ang(adj,opp);
// vim: expandtab tabstop=4 shiftwidth=4 softtabstop=4 nowrap