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Adam
Joined: 01 Dec 2006 Posts: 61 Location: Sequim, WA

Posted: Sat Mar 27, 2010 11:05 pm Post subject: creating 3D Surface Coordinates 


Is it possible to create a 3D Surface Coordinates object from a 3D Surface? I'd like to create a 3D Surface Texture by mapping an aerial image to an elevation dataset, which is a triangular mesh/3D Surface. I've been looking at DTSource, but I'm confused about the purpose of the u/v vectors.
My current workaround is to create a 3D Surface Values with one channel of the bitmap, but that limits me to grayscale and is kind of clunky due to some reinterpolation. 

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David Site Admin
Joined: 25 Nov 2006 Posts: 1969 Location: Chapel Hill, NC

Posted: Sun Mar 28, 2010 1:34 am Post subject: 


You mean you want to take a surface and map (x,y,z) into something like (x,y). That is (u,v) = (x,y). This would then assume you have a bitmap that will contain the (u,v) locations. Note that (u,v) are coordinates in 2D. I'm not mapping this on [0,1]x[0,1].
So for example the code will define the 2D coordinates on the surface to be (x,y):
Code:  DTSurfaceCoordinates3D Computation(DTSurface3D surf)
{
DTFloatArray points = surf.Points();
int howMany = points.n();
int i;
DTMutableFloatArray U(howMany);
DTMutableFloatArray V(howMany);
for (i=0;i<howMany;i++) {
U(i) = points(0,i);
V(i) = points(1,i);
}
return DTSurfaceCoordinates3D(surf,U,V);
}

If you have a 300x300 bitmap with dx=dy=1, you need the xy range of the surface to be inside the box [0,300]x[0,300], for example hand in a sphere with radius 120 and center (150,150,0). Then attach the grid and bitmap using the "Coordinates and Bitmap" module inside a "3D Surface Texture" variable.
David 

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Adam
Joined: 01 Dec 2006 Posts: 61 Location: Sequim, WA

Posted: Sun Mar 28, 2010 2:33 pm Post subject: 


David wrote:  You mean you want to take a surface and map (x,y,z) into something like (x,y). 
I'm glad you figured out what I meant . Yes, that works perfectly, and is just what I was looking for. Thanks! 

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