Terrain Normals

Blitz3D Forums/Blitz3D Programming/Terrain Normals

JoshK

(Posted 2004) [#1]

I have the following points on a terrain, each with a height:

A B C
D E F
G H I

I want the normal for the center point E. All I have are the following values.

The height of each point:
Ay#, By#, Cy#, Dy#, Ey#, Fy#, Gy#, Hy#, Iy#

And the distance between points:
pointspacing#

The terrain is 1 unit high x 1 unit wide x 1 unit deep.

My normals are coming out okay right now, but they look blocky, not smooth.

Dreamora

(Posted 2004) [#2]

you need to calculate the face normals around E and normalize the averange normal of all surounding face normals of E.

JoshK

(Posted 2004) [#3]

I am looking for something faster that doesn't use triangles. I store terrain as a grid of points, and only update the mesh to fit the grid.

Tom	(Posted 2004) [#4]

Is UpdateNormals too slow?

Couldn't you cheat and cut the number of trinormal calcs in half? Instead of possibly 8 tri normals, use 4:

E normal = Average of trinormals EDB EBF EFH EHD

Won't be perfect unless EDB EBF EFH EHD 'are' the actual tris, if your terrain is built in an ordered fashion, E would normaly have 6 tris connected to it, unless it was at an edge:

EDB EBC ECF EFH EHG EGD

I can't see how you can get trinormals without doing cross products though.

JoshK

(Posted 2004) [#5]

It seems like you should be able to calculate it purely from the surrounding four points B,D,F,H. I am doing this right now, but it is not very smooth.

Calculate the x component of the normal:

nx#=0

     D
     x    
B         F
x         x

nx#<0

     D
     x    F
B         x
x

nx#>0

     D
B    x    
x         F
          x

AramusM

(Posted 2004) [#6]

Hmm, i think you can only calculate it from the surrounding 4 points if your tri setup is as below

A--B--C
| / | \ |
D--E--F
| \ | / |
G--H--I

Then you calculate the normal for BEF, BDE, DEH and EFH. add the four normals vectors together and normalize.

If its

A--B--C
| / | / |
D--E--F
| / | / |
G--H--I

You will have to get the normals for DBE, BCE, ECF, DEH, GEH and EFH. Add the 6 normals together and normalize. I think thats whats needed(Cant be sure its been a while)

JoshK

(Posted 2004) [#7]

Yeah, I ended up calculating the surrounding planes, although these are not related to the triangles on the representative mesh. The nice thing about this system is I can generate a mesh from the point data, with any number of subdivisions or LOD.

   B
 / | \
D--E--F
 \ | /
   H