Re: [Algorithms] Terrain Normals

[Pai-Hung C. <pa...@ac...>]

Hi,

How can your bilinear filtering method (as depicted below) be used with the
terrain layout (as depicted at bottom, the same as mine)?

Thank you,

Pai-Hung Chen


> I use a form of bilinear filtering to calculate my vertex normals, like
so:
>
> +-----+
> |\ 1 /|
> | \ / |
> |4 X 2|
> | / \ |
> |/ 3 \|
> +-----+
>
> Where the normal of vertex X is the average of the normals of triangles
> 1...4. Note that the above does _not_ represent the actual layout of my
> terrain mesh, which has the following (probably quite familiar) layout:
>
> +-----+
> | /| /|
> |/ |/ |
> +--+--+
> | /| /|
> |/ |/ |
> +-----+
>
> This seems to work when it comes to avoiding the gray bands you are
> referring to.
>
> Hope this helps,
>
> Jim Offerman
>
> Innovade
> - designing the designer
>
> ----- Original Message -----
> From: "Pai-Hung Chen" <pa...@ac...>
> To: <gda...@li...>
> Sent: Monday, August 14, 2000 8:22 AM
> Subject: [Algorithms] Terrain Normals
>
>
> > Hi,
> >
> > I've written a routine to read a bitmap heightfield and construct a
> terrain
> > mesh from it.  I partition each set of four pixels into two triangles
> along
> > the upper-right-to-lower-left diagonal line.  Therefore, for example, a
> 128
> > x 128 bitmap will produce (128-1) x (128-1) x 2 = 32258 triangles using
my
> > method.  For each triangle I caculate its unit face normal.  For each
> vertex
> > of a triangle, I calculate its vertex normal by adding and averaging the
> > face normals of all triangles that share the vertex (in my case a vertex
> can
> > be shared by at most six triangles and at least one triganle) and then
> > normalize the averaged normal, which is used in redering.  My problem is
> > that there are some *horizontal dimmed banding* effects along the
triangle
> > edges of the mesh when rendering in D3D with light cast on it.  Also,
> there
> > are very visible dimmed seams between triangles when light is cast on
it.
> > All these artifacts seem to manifest only when light is cast in large
> angles
> > (i.e. not directly).  Is it because the arrangement of triangles in my
> mesh
> > is too *uniform* (actually they are extremely uniform)?  Or is my
> > calculation of vertex normals incorrect?
> >
> > Thanks in advance,
> >
> > Pai-Hung Chen
> >
> >
> >
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>
>
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