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# angle of 2 normals

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this is a question on how to get the angle between 2 normals... I read numerous places that you use the Dot Product of the 2 normals, but that does not return in the form of an angle! can anyone help me? Edited by - rpgman on August 2, 2001 4:22:41 PM

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if the two normals ( or simply, the two vectors ) are length 1, the returnvalue of the dotproduct is the cosine of the angle between the two vectors.. to get the angle, just use the "inverse cosine", arcus cosinus, or arc-sine in english, to get it, means float angle = acosf( dot( normalize( v0 ), normalize( v1 ) );

but normaly you dont need the angle, just the acosf, except you need to call something like glRotatef or such stuff..

we wanna play, not watch the pictures

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This is the formula you need...

If A and B are vectors and q is the angle between them, then

A.B = |A| * |B| * cos(q)

where A.B refers to the dot product of the two vectors and |A| refers to the length (or magnitude) of the two vectors.

So to get the angle q, find the dot product, and then divide that by the product of lengths of the two vectors, and then take the arc-cosine of it.

~ Dragonus

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