Re: [Algorithms] Terrain Normals

[Jim O. <j.o...@in...>]

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
>
>
>
> _______________________________________________
> GDAlgorithms-list mailing list
> GDA...@li...
> http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
>