Voxel fields usually induce an intrinsic coordinate system that
is defined by their voxel numbers in all of their dimensions.
A voxel field that has an inplane resolution of 512x320 with
200 slices thus induces a local coordinate system win which
coordinates are integer vectors in the range [0-511], [0-319], [0-199].
When subvoxel precision is used, the vectors are double and
ranges can be [0-512[, [0-320[, [0-200[. Voxel centers are assumed
to be at x.5, y.5, z.5.
[0-511[,
As these local coordinates are not necessarily isotropous, a global
coordinate system is introduced that is always isotropous and has
a fixed mapping to real world sizes. 1 unit of the global coordinate
system usually maps to 1mm, unless explicitly noted otherwise.
(Some applications, like microtomography or laser-fluorescence
microscopy work on a µm scale, so using mm scaled coordinate
systems would not be appropriate).
Most Eccet commands take coordinates as appropriate for the object
in question. Commands manipulating global objects like cameras,
cutplanes, tristrips and splines work in the global coordinate
system, while commands manipulating volumes usually work in
the coordinate system local to the current volume.