Difference between revisions of "Volume center"

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Revision as of 09:16, 28 April 2016


The center of a discretized volume can be defined in different ways. Dynamo uses the same convention in all its functions. For the formulas in this page, remember also that Dynamo uses the convention of counting pixels with the index 1, (not 0). The pixel "on the corner" with the first coordinates in a volume V is thus denoted as V[1,1,1].

We use the notation [ i,j,k] for pixel indices.


Direct space

For a volume of V NxNxN pixels, Dynamo considers the pixel located at [N/2+1,N/2+1,N/2+1] as the center of V

Rotation

Rotation needs defining on a concrete point, not on a pixel (as a pixel is actually a square with an area). The convention in Dynamo is to define the rotation center point in the middle of the center pixel

Note that the center is defined as point, not as a pixel.

Placing templates in a Volume

Sometimes you need to place a template T inside a bigger volume V, by passing a pixel coordinate r inside the bigger volume. In such cases the placement follows by setting the central pixel [N/2+1,N/2+1,N/2+1] at the pixel position r in V, i.e.:

V[x-N/2 : x+N/2-1 , y-N/2 : y+N/2-1, z-N/2 : z+N/2-1] = T[:,:,:];


Fourier space