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Wed Jun 23 07:25:26 2010 UTC (9 years ago) by glk
File size: 4868 byte(s)
Wed Jun 23 07:25:26 2010 UTC (9 years ago) by glk
File size: 4868 byte(s)
clarified restriction between dimension and space dimension
The ASCII lines in the header end with '\n'. First line should be the magic: NRRD0004 Rest of header will be a sequence of plain text lines, terminated by an empty line ('\n' alone). Some header lines give per-array information, some give per-axis information. Note that the distinction between scalar and non-scalar images is given by the per-axis "kinds" field, so that is where further information is given about the constraints associated iwth non-scalar image data. ============================================================ The basic fields that should be there are: ---------------- type: <string> Gives the type of the scalar values in the array. Current values are: signed char unsigned char short unsigned short int unsigned int long long int unsigned long long int float double ---------------- dimension: <int> Gives the dimension of the array. Must be greater than 0. Current code has a #define that limits the value to <= 16. The per-axis fields will have this many pieces of information. ---------------- encoding: <string> How scalar values are encoded on disk. Currently, should only see "encoding: raw". ---------------- endian: <string> Endian-ness of raw values saved on disk. Possibilities are: little big ---------------- space dimension: <int> Gives the dimension of the world-space in which the array or oriented (For now we're not allowing the named spaces that are given with the "space: " field). The points and vectors given by "space origin" and "space directions" will have this many coefficients, so this field has to precede "space origin" and "space directions". ---------------- space origin: (<float1>,<float2>,...,<floatN>) Gives the location of the center of the first sample (with index space coordinates (0,0,0,...,0). The number of coefficients separated by commas and bounded by parens (with optional whitespace throughout) is given by the "space dimension" field. Each coefficient is a floating point value (of the sort produced by printf("%g", val)) ============================================================ The per-axis fields that should be there are as follows. The ordering of these fields is always *fast* to *slow*, and the number of pieces of information is always equal to the image dimension. ---------------- sizes: <int1> <int2> ... <intD> The number of samples along each axis. Each integer value must be >= 0. ---------------- kinds: <string1> <string2> ... <stringD> The kind of information represented by the samples along each axis. The possible values are: 2-vector 3-vector 4-vector 2D-symmetric-matrix 2D-matrix 3D-symmetric-matrix 3D-matrix space The "space" kind is for a typical axis of the image, with samples that subtend some region of the spatial domain of the image. All the other kinds are the sequence of scalar values that compose a non-scalar image value (vectors and tensors). We currently allow there to be *at* *most* *one* axis with a non-"space" kind. We can have non-scalar image values, but we don't have cartesian products of non-scalar image values. The non-"space" kind can be anywhere in the axis ordering. If all the axis kinds are "space", then then image data is for scalars, else it is for non-scalar data. In scalar data, the image "dimension" must equal the "space dimension". In non-scalar data, the image "dimension" must equal *one* plus the "space dimension". That is, the spatial axes have to form a basis, not necessarily orthonormal, for world space (the vectors are defined by the "space directions" field, below). Thus, a 3-D scalar image can't reside in a 2-D or 4-D world space, nor can a 3-D vector image reside in a 3-D or 5-D world space. We are currently not allowing the "measurement frame" field that identifies the coordinate system in which these are measured relative to the image orientation, so nothing should be assumed about the space in which these coefficients are measured. The order of coefficients for these non-scalar kinds is: 2D-symmetric-matrix: Mxx Mxy Myy 2D-matrix: Mxx Mxy Myx Myy 3D-symmetric-matrix: Mxx Mxy Mxz Myy Myz Mzz 3D-matrix: Mxx Mxy Mxz Myx Myy Myz Mzx Mzy Mzz ---------------- space directions: (<x1>,<x2>,...,<xN>) (<x1>,<x2>,...,<xN>) ... (and at most one of these vectors is actually "none") These give the "direction" in world-space between successive samples along each axis: the columns of the index-to-world transform matrix. There is one per image axis, even for the axis of coefficients of non-scalar image values. Because such an axis really has no spatial extent, for this and only this axis, the space direction vector is instead the string "none". ============================================================ Field ordering: The fields should appear in this order: type dimension space dimension sizes space directions kinds endian encoding space origin
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