RE: [Algorithms] Geodesic Sphere

[Steve W. <Ste...@im...>]

This problem is difficult since all three sides of all triangles will be
equal.  It requires dividing a sphere longitudinally by X number of
triangles while dividing it laterally by Xsin(pi/3) = X * [sqr(3)/2] and
where sqr(3)/2 * X is a whole number or whole fraction...and offhand I can't
think of any whole number X where multiplying it by sqr(3)/2 will result in
something like 8 or 1/2.

I suggest using isosceles triangles since the algorithm is much simpler and
I posted it earlier concerning spherical texture mapping...here's a clip
from it (yes it's in basic...hope you can read it):

For example here's how I create a sphere:

Dim pi as single
Dim pi2 as single

Dim spherecount as long
Dim spherename() As String
Dim spherevertexcount As Long

Dim sphereradius(1) As Single
Dim spherecenter(1) As D3DVERTEX
Dim spheredx7vertex(1100) As D3DVERTEX

pi=3.14159265
pi2=pi * 2

spherecount = 1
spherename(1) = "Sphere 1"
spherecenter(1).x = 0
spherecenter(1).y = 4
spherecenter(1).z = 6
sphereradius(1) = 1			'radius

c = 16	'number of sections...smaller c means larger triangles, larger c
means smaller triangles
b = 0
For cameraangle.x = 0 To pi * (c - 1) / c + 0.0001 Step pi / c
 For cameraangle.y = 0 To pi2 + 0.0001 Step pi / c
  b = b + 1
  dx7.CreateD3DVertex sphereradius(1) * Sin(cameraangle.y) *
Sin(cameraangle.x) + spherecenter(1).x, sphereradius(1) * Cos(cameraangle.x)
+ spherecenter(1).y, sphereradius(1) * Cos(cameraangle.y) *
Sin(cameraangle.x) + spherecenter(1).z, Sin(cameraangle.y) *
Sin(cameraangle.x), Cos(cameraangle.x), Cos(cameraangle.y) *
Sin(cameraangle.x), cameraangle.y / pi2, cameraangle.x / pi,
spheredx7vertex(b)
  b = b + 1
  dx7.CreateD3DVertex sphereradius(1) * Sin(cameraangle.y) *
Sin(cameraangle.x + pi / c) + spherecenter(1).x, sphereradius(1) *
Cos(cameraangle.x + pi / c) + spherecenter(1).y, sphereradius(1) *
Cos(cameraangle.y) * Sin(cameraangle.x + pi / c) + spherecenter(1).z,
Sin(cameraangle.y) * Sin(cameraangle.x + pi / c), Cos(cameraangle.x + pi /
c), Cos(cameraangle.y) * Sin(cameraangle.x + pi / c), cameraangle.y / pi2,
(cameraangle.x + pi / c) / pi, spheredx7vertex(b)
 Next
Next

spherevertexcount = b
vertexperstrip = c * 4 + 2

d3d7device.SetTexture 0, dd7surface(7)  'sphere
For b = 1 To spherevertexcount - vertexperstrip + 1 Step vertexperstrip
 Call d3d7device.DrawPrimitive(D3DPT_TRIANGLESTRIP, D3DFVF_VERTEX,
spheredx7vertex(b), vertexperstrip, D3DDP_DEFAULT)
Next



> -----Original Message-----
> From: Aldo . [mailto:al...@ho...]
> Sent: Tuesday, August 22, 2000 5:45 AM
> To: gda...@li...
> Subject: [Algorithms] Geodesic Sphere
> 
> 
> 
> Hi!
> 
> I'm looking for an algoritm to create a geodesic sphere(is the name 
> correct?), a sphere made of equilateral triangles. I would be 
> nice if I 
> could choose the resolution(more or less triangles).
> 
> 
> 
> Thanks in advance.
> 
> Aldo Spanghero
> 
> 
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