When I create an object, say a cylinder made from a triangle fan, is there a

way to extract the normals from each of the vertices (or faces?).

Thanks,

Jon

When I create an object, say a cylinder made from a triangle fan, is there a

way to extract the normals from each of the vertices (or faces?).

Thanks,

Jon

For all three vertices of a given triangle, you can find the common normal

by taking the crossproduct of the two vectors formed by a given vertex and

the other two vertices: v1 = p1 - p0; v2 = p2 - p0; n = v1 x v2. For a

smoother looking cylinder, you can take the average of the normals at a

given vertex.

>When I create an object, say a cylinder made from a triangle fan, is there

a

>way to extract the normals from each of the vertices (or faces?).

>Thanks,

>Jon

>For all three vertices of a given triangle, you can find the common normal

>by taking the crossproduct of the two vectors formed by a given vertex and

>the other two vertices: v1 = p1 - p0; v2 = p2 - p0; n = v1 x v2. For a

>smoother looking cylinder, you can take the average of the normals at a

>given vertex.

>>When I create an object, say a cylinder made from a triangle fan, is there

>a

>>way to extract the normals from each of the vertices (or faces?).

axes, the surface normal at any given vertex is the vertex, with 0

substituted for the central axis value. (For example, for a cylinder

centered on the Z axis, take the vertex and replace the Z value with zero;

the result is the normal at that vertex.)

You will typically want to make this normal of unit length.

-Paul Martz

Hewlett Packard Workstation Systems Lab

To reply, remove "DONTSPAM" from email address.

Thank you. I will be needing that information on what I should make theQuote:>For the special case of a cylinder centered on one of the three coordinate

>axes, the surface normal at any given vertex is the vertex, with 0

>substituted for the central axis value. (For example, for a cylinder

>centered on the Z axis, take the vertex and replace the Z value with zero;

>the result is the normal at that vertex.)

>You will typically want to make this normal of unit length.

normals. However, I would like to know a way to find out what the normals

already are for a given figure. Is there a way to query that information?

Jon

Thank you. That information on what normal vector I should make will beQuote:>For all three vertices of a given triangle, you can find the common normal

>by taking the crossproduct of the two vectors formed by a given vertex and

>the other two vertices: v1 = p1 - p0; v2 = p2 - p0; n = v1 x v2. For a

>smoother looking cylinder, you can take the average of the normals at a

>given vertex.

quite useful. However, for the moment I need to know a way to query the

existing normals for a given figure.

Jon

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I`m sure I saw a post about this about a week ago or so.. but I can`t find

it now.

Could anyone shed some light on finding the vertex normals for

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P.S. I`m not a great maths head (I`m working on it) so be gentle with me.

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