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General Outline and Data Structure of Images

Section basically up to date

The GILDAS software is designed to work in an heterogeneous network, where each computer may have its own floating point and integer number representation and its own operating system. Images created on any computer should be accessible transparently from any other computer in the network.

To allow such a portability and yet preserve efficiency when working on a single type of machines, all files are written in the binary representation of the machine on which they were created. A library of subroutines is used to access the images and perform the necessary format conversion between the different representations of real and integer numbers. So far, 3 representations are recognized: VAX format (a dead dinosaur...), IEEE format (the so-called big-endians, like DEC DS Workstation, Intel & AMD PCs and most affordable current computers) and EEEI format (big-endians, like Sun SparcStation, IBM RS-6000 series, and other obsolescent machines...).

The images have the following organization :

The header starts with 'GILDAS', followed by one character which indicates the type of integer and floating point number representation

The last 3 cases are inherited from the GDFV1 data version, in which all size informations were limited to 32-bit numbers. The latest GDFV2 data version has some integers using 64 bit values to handle large data sets.

After the version/hardware sign, an extra text indicates the type of information in the image:

This character string, being human readable, is intended for quick checks, but a more specific information about the actual type of data file is available through an integer code in the data header.


next up previous contents index
Next: Fortran-90 access to images Up: Task Programming Manual Previous: Task Programming Manual   Contents   Index
Gildas manager 2014-07-01