NRRDLoader: Fix spacing issue when loading 16 bit images.

[LinkunGao]

Fixed #25718

Description

• To correctly display the nrrd images, we need to display the millimeter, not the pixels.
  • When we load the nrrd image, we need to convert pixels to millimeters should Based on this formula:
  • pixels * space = millimeters
  • So the RASDimention show the width, height, and depth millimeter of nrrd image.

Thus in the code we can use this formula to get the image's real distance:

volume.RASDimensions = new Vector3(
      Math.floor(volume.xLength * spacingX),
      Math.floor(volume.yLength * spacingY),
      Math.floor(volume.zLength * spacingZ)
   ).toArray();

• To get the 16-bits nrrd images' correct space in threejs environment, we don't need a normalized direction.

This contribution is funded by Load breast image

[Mugen87]

Let's give this a try!