sphere mapping question (openGL)

[Frankolinox]

topic: openGL

a) hi all.. how I can create a sphere mapping for an earth pic?

b) how I can create an uv sphere mapping with an earth texture?

thanks, regards, frank

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[Mike Lobanovsky]

Hi,

If we assume the sphere precision nPrecision as half the number of sphere faces (32 will be enough for starters), M_PI_2 as Pi / 2, and M_TWOPI as Pi * 2, then:

Code: [Select]

For i = 0 To (nPrecision - 1) \ 2
theta1 = i * M_TWOPI / nPrecision - M_PI_2
theta2 = (i + 1) * M_TWOPI / nPrecision - M_PI_2

glBegin(GL_TRIANGLE_STRIP)
For j = 0 To nPrecision
theta3 = j * M_TWOPI / nPrecision

' Splices
ex = cos(theta2) * cos(theta3) ' calculate Euler angles on 3 axes
ey = sin(theta2)
ez = cos(theta2) * sin(theta3)

glNormal3f(ex, ey, ez) ' set up normals
glTexCoord2f(-j / nPrecision, 2 * (i + 1) / nPrecision) ' set up UVs
glVertex3f(1.5 * ex, 1.5 * ey, 1.5 * ez) ' render vertices

' Sides
ex = cos(theta1) * cos(theta3)
ey = sin(theta1)
ez = cos(theta1) * sin(theta3)

glNormal3f(ex, ey, ez)
glTexCoord2f(-j / g_nPrecision), 2 * i / nPrecision)
glVertex3f(1.5 * ex, 1.5 * ey, 1.5 * ez)
Next
glEnd()
Next
Declare all the variables in the above code As Single, except for i and j which should be defined As Long (or Sys).  Put this code into your render procedure. Then if God permits, you'll get the following picture: (incidentally, this FBSL example uses a similar texture)

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[JRS]

Here is the NASA Blue Marble equirectangular projection in a Java applet. It tends to give the feeling as if the earth is inside out and your viewing from the center. What is amazing about the image is it's acuracy when the long/lat is feed to Google maps. Drag the image with your mouse to pan (zooming optional) and press the map button to sync with Google maps.

FYI You need to have Java Applet plugin support for this example to work in your browser. Current Chrome no longer supports Java so Firefox is your best bet.

NASA Blue Marble - Viewer/Google Maps sync




 

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[Mike Lobanovsky]

... so Firefox is your best bet.

Hi John,

... but not under XP. Modern Java updates are no more compatible with XP and require at least Vista. Anyway thanks for the lead. I'll study it when I'm under my Vista or 7.

Frankolinox' texture is specifically designed to be used with the GL_TRIANGLE_STRIP sphere rendering algo whereby polar UVs tend to be infinitely small, and it can't be effectively used in any other sphere rendering modes. There are some other algos that render the polar regions of a sphere practically without distortion but they can't be used with this particular texture layout. Hence my example code.

[Charles Pegge]

Thanks Mike,

I have included an example with your code. ProjectsA/OpenglCns/SphereMapPolar.o2bas

Earth.bmp is converted to Earth.jpg

The texture loader has also been tweaked to support rectangular images. (512*256.

Code: OxygenBasic

1.   % Title "Sphere Mapping Demo"
2.   % Animated
3.   % ScaleUp
4.  '% PlaceCentral
5. '% AnchorCentral
6.  include "$\inc\ConsoleG.inc"
7.  
8.   function SphereMap(sys nPrecision)
9.   ==================================
10.   'Mike / Sphere mapping
11.  float ex,ey,ez,theta1,theta2
12.   float M_TWOPI = pi()*2
13.   float M_PI_2  = pi()/2
14.   sys   i,j,ei
15.   ei=(nprecision-1)\2
16.   For i = 0 To ei
17.     theta1 = i * M_TWOPI / nPrecision - M_PI_2
18.     theta2 = (i + 1) * M_TWOPI / nPrecision - M_PI_2
19.     glBegin(GL_TRIANGLE_STRIP)
20.     For j = 0 To nPrecision
21.       theta3 = j * M_TWOPI / nPrecision
22.       ' Splices
23.      ex = cos(theta2) * cos(theta3) ' calculate Euler angles on 3 axes
24.      ey = sin(theta2)
25.       ez = cos(theta2) * sin(theta3)
26.       glNormal3f(ex, ey, ez) ' set up normals
27.      glTexCoord2f(-j / nPrecision, 2 * (i + 1) / nPrecision) ' set up UVs
28.      glVertex3f(1.5 * ex, 1.5 * ey, 1.5 * ez) ' render vertices
29.      ' Sides
30.      ex = cos(theta1) * cos(theta3)
31.       ey = sin(theta1)
32.       ez = cos(theta1) * sin(theta3)
33.       glNormal3f(ex, ey, ez)
34.       glTexCoord2f(-j / nPrecision, 2 * i / nPrecision)
35.       glVertex3f(1.5 * ex, 1.5 * ey, 1.5 * ez)
36.     Next
37.     glEnd()
38.   Next
39.   end function
40.  
41.   sub main()
42.   ==========
43.   static sys   imgn,res,wi,ht,earth
44.   static float ang
45.   if not imgn
46.     imgn=21
47.     res=0 'use image wi and ht (512*256)
48.    LoadTexture "..\..\examples\images\Earth.jpg",imgn,res,wi,ht
49.     earth=CompileList : SphereMap 32 : glEndlist
50.   end if
51.   cls 0,0,0
52.   'display image
53.  '
54.  pushstate
55.   move 16,-16
56.   shading
57.   color 1,1,1,1
58.   texture imgn
59.   scale 6
60.   rotateY ang
61.   go earth
62.   'quadnorm 10.0, 10.0 'apply image texture to quad
63.  texture 0
64.   popstate
65.   flat
66.   move 0,-.5
67.   scale 2
68.   printl "Sphere Mapping"
69.   ang+=.5 : if ang>=360 then ang-=360
70.   end sub 'main
71.  
72.   EndScript
73.  

[Mike Lobanovsky]

Hi guys,


@John:

Nah, my Win 7 FF refuses to display the applet. It says AllBasic is untrusted as far as Java sources go.

But your Earth texture is ... gorgeous! Thanks!


@Charles:

Thanks for your confidence in my code.

But John's (NASA) texture looks absolutely awesome on this sphere in place of my poor 512x256 shred, and especially when it has more faces than 32 * 2, for instance, SphereMap 128.

[JRS]

Nah, my Win 7 FF refuses to display the applet. It says AllBasic is untrusted as far as Java sources go

  I think you would really be impressed with our (early pano days) old 360 virtual tour viewer I used to display the Blue Marble. The Google interface is icing. I got it working on Firefox under Linux with the Ice Tea Java applet support plug-in. Promise, it will be worth the extra effort on your part.

Just accept the warning messages as the viewer is a 2003-2005 vintage Java JAR applet.



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[Charles Pegge]

Mmmm yes, this one is rather nice too

http://www.johnstonsarchive.net/spaceart/earthmap.jpg



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[JRS]

Blue Marble - Next Generation Very high resolution images.

Here is a newer version of the viewer for Windows, Linux and Mac.

http://www.fsoft.it/FSPViewer/

Using this viewer doesn't have my Google Maps interface but still fun to play with.

[Frankolinox]

thank you mike and charles for help nice week for you