Volume File Format

OpenQVis uses a simple file format for volume data sets. Every data set consists of a header file (extension *.dat) in ASCII format and a data file (extension *.raw) in binary format. The header file contains information about the size and format of the data file. A typical example of such an ASCII file is displayed in the figure left. Note that the file format originated from the the University of Erlangen, Germany and was used to describe a large amount of different kinds of data. Thus it contains some entries which are not relevant for OpenQVis.

The header file must contain the following entries:

ObjectFileName:  The object file name refers to the name of the data file, which contains the raw voxel data. This can be either an absolute path or a relative path with respect to the storage position of the dat file.
TaggedFileName:  The tagged file name refers to an optional optional data which contains additional segmentation data in the form of voxel tags. This can be either an absolute path or a relative path with respect to the storage position of the dat file. If no such file is available, the entry should be set to "---" (three minus signs)
Resolution:  The volume data set consists of a large array of voxel values. The resolution of the data set is given by the number of voxels in x-, y- and z- direction.
SliceThickness:  The size of one voxel in x-, y- and z- direction (usually in millimeters).
Format:  The data format of one voxel. Can be either UCHAR (8 bit) or USHORT (16 bit). Note that, depending on the selected draw style, OpenQVis my internally convert 16 bit values to 8 bit!
NbrTags:  The number of different tag numbers contained in the tag file. The value is simply ignored if there is no tag file specified in line 2 of the dat file.
ObjectType:  must be set to TEXTURE_VOLUME_OBJECT
ObjectModel:  must be set to RGBA.
GridType:  must be set to EQUIDISTANT.

The data file simply contains the raw voxel data as a large binary array which is indexed as
voxel(x,y,z) = array[z * YDIM * XDIM + y * XDIM + x],
with XDIM, YDIM and ZDIM referring to the resolution of the data set, as specified in line 3 of the header file. For 16 bit data, the data may be stored either in big endian or little endian format. The correct byte ordering must be chosen in the Preference dialog in the Options menu of OpenQVis.

Volume File Format

 ObjectFileName: CT_Head_large.raw
 TaggedFileName: ---
 Resolution: 512 512 106
 SliceThickness: 0.435547 0.435547 2.0
 Format: UCHAR
 NbrTags: 0
 ObjectModel: RGBA

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