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Dihedral Angle


DihedralAngle

The dihedral angle is the angle theta between two planes. The dihedral angle between the planes

a_1x+b_1y+c_1z+d_1=0
(1)
a_2x+b_2y+c_2z+d_2=0
(2)

which have normal vectors n_1=(a_1,b_1,c_1) and n_2=(a_2,b_2,c_2) is simply given via the dot product of the normals,

costheta=n_1^^·n_2^^
(3)
=(a_1a_2+b_1b_2+c_1c_2)/(sqrt(a_1^2+b_1^2+c_1^2)sqrt(a_2^2+b_2^2+c_2^2)).
(4)

The dihedral angle is therefore trivial to compute via equation (3) if the two planes are specified in Hessian normal form

 n_i^^·x=-p_i
(5)

for planes i=1,2 (Gellert et al. 1989, p. 541).

The dihedral angle between planes in a general tetrahedron is closely connected with the face areas via a generalization of the law of cosines.


See also

Angle, Contact Angle, Hessian Normal Form, Line-Line Angle, Plane, Plane-Plane Intersection, Tetrahedron, Trihedron, Vertex Angle

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References

Gellert, W.; Gottwald, S.; Hellwich, M.; Kästner, H.; and Künstner, H. (Eds.). VNR Concise Encyclopedia of Mathematics, 2nd ed. New York: Van Nostrand Reinhold, 1989.Kern, W. F. and Bland, J. R. Solid Mensuration with Proofs, 2nd ed. New York: Wiley, p. 15, 1948.

Referenced on Wolfram|Alpha

Dihedral Angle

Cite this as:

Weisstein, Eric W. "Dihedral Angle." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DihedralAngle.html

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