next up previous contents
Next: Coding Examples Up: Dimensions and coordinate systems Previous: Dimension Attributes   Contents

Voxel and World Coordinate Systems

MINC 2 defines both ``voxel'' and ``world'' spatial coordinate systems. For each dimension, the world coordinate conversion is specified by a pair of attributes: step and start. The xspace world coordinate, for example is calculated using x = v*step + start, where x is the x world coordinate and v is the voxel count (starting at zero). Thus the magnitude of the step attribute specifies the distance between voxels and the sign of the step attribute specifies the orientation of the axis. MINC files are allowed to have non-orthogonal axes with the dimensions not perfectly aligned with the named axis. There can be a direction_cosine attribute that gives the true orientation of the axis. For example, normally the xspace dimension should line up with the world x axis, ie. direction cosine = (1,0,0) ; however, it is possible to have a direction cosine of (0.9, 0.43589, 0). For detailed formulas please refer to APPENDIX A, section 2.1 The MINC 2.0 File Format by Robert D. Vincent.
next up previous contents
Next: Coding Examples Up: Dimensions and coordinate systems Previous: Dimension Attributes   Contents
Robert VINCENT 2004-05-28