Generate arguments for scatter3() from volumetric data in Matlab - matlab

Question

I used to render my volumetric data with isosurface(), but now I would like to render them as points to accelerate the speed.
The data I have is a 3D array, representing a 3D object. If a voxel belongs this object, then its value is 1, otherwise it is zero.
In order to use scatter3(), I need to generate coordinates for those voxels that have value 1. I currently use the following code to do the job:
function [ x, y, z ] = scatter3_assist( volume )
[R, C, D] = size(volume);
x = zeros( size(volume(:)) );
y = x;
z = x;
idx = 1;
for d=1:D
for r=1:R
for c=1:C
if volume(r, c, d) == 0
x(idx) = 0; y(idx) = 0; z(idx) = 0;
else
x(idx) = C - c + 1; y(idx) = R - r + 1; z(idx) = d;
end
idx = idx + 1;
end
end
end
x(x==0) = [];
y(y==0) = [];
z(z==0) = [];
x = x - 1;
y = y - 1;
z = z - 1;
end
The return value x, y, z are the coordinates of the voxels that belong to my object, and then I called scatter3(x, y, z, '*'); to render it.
Are there any more efficient ways to generate coordinates for specific voxels used by scatter3()?

Answer 1

I would suggest using find to find the linear indices of non-zero entries in your array and then use ind2sub to convert to indices and perform whatever transformation you need to get x, y, and z. Something like:
I = find(volume ~= 0);
[y, x, z] = ind2sub(size(volume),I); %// note that x and y are switched as in your code above
x = size(volume,2)-x;
y = size(volume,1)-y;
You'll want to double check those operations on x and y to make sure they're equivalent to what your code does.