Instead of specifying the voxel resolution it is also possible to
specify the size of the output image matrix using '-xdim,-ydim,-zdim'.
If these parameters are set to '0' then a default size is used.
In the following example, an input image is scaled to a voxel resolution
of 3x3x3 mm.
vmapscale -in map.v -out result.v -xreso 2.5 -yreso 2.5 -zreso 2.5