This format corresponds to the format of the SPOT scene digital products.
These digital products are delivered either on 1/2" magnetic tapes (6250 bpi CCT), Exabytes or on CD-Rom.
It is also called the "CAP format", since it was produced for the "Centre d'Archivage et de Prétraitement (CAP)", located at Spot Image in Toulouse as well as SSC-Satellitbild facilities in Kiruna.
This format concerns the SPOT scenes which are processed at level 1A, 1B, 2A or 2B.
This format is upward compatible with the old SPOT Standard Product CCT format and is capable of handling the additional Short Wave Infra-Red (SWIR) band on SPOT 4.
The files in a single SPOT Product Logical Volume are:
The files are separated by END OF FILE (EOF) tape marks. The Null Volume Directory File is followed by three EOFs designating an END OF SET (EOS).
Imagery records can have a fixed length of one of the following depending on the length of the image line:
3960 bytes (split record size option)
5400 bytes (line length < 5300 pixels)
8640 bytes (5301 < line length < 8450 pixels)
10980 bytes (8541 < line length < 10880 pixels)
To accommodate image processing systems that cannot read large image record lengths, a split record format is available. Digital scenes produced using this option have a maximum record length of 3960 bytes and are only available on 1600 bpi magnetic tapes.
The Volume Directory File is the first file on any SPOT CCT and contains information about the logical volume. It consists of five records of 360 bytes each:
The Volume Descriptor record identifies the logical volume within a volume set and the number of files on this volume. Each Pointer record references one of the three data files in the logical volume and identifies the file format used to read the file. The Text record contains information about the creation of the tape and is useful in identifying the tape.
The Leader File contains auxiliary information related to the SPOT scene (identification parameters defining the geometry and the radiometry of the scene, preprocessing data, etc.). The leader file consists of 27 records of 3960 bytes each:
The Header record contains information about the scene identification, the scene characteristics including corner latitude and longitude coordinates, the mission, the preprocessing done to the scene and the organization of the Ancillary Data records which follow.
The remaining records in the Leader file contain information which can be used to do further processing (radiometric or geometric) and on the preprocessing applied to the raw SPOT scene.
An Imagery File contains one file descriptor record repeated on each physical volume in the case of multi-volume scenes and; image data records, the total number depending on the spectral mode and level of processing.
The Imagery Descriptor record variable segment gives the number and length of the imagery records; how the image pixels are packed, the left and right margin locations and the size of the prefix and suffix data. The range of values for each pixel is between 1 and 255. A pixel count of 0 corresponds to a nonsignificant radiometric value and is reserved for margins around the imagery data, and for level 1A bad data lines and dead detectors.
The Trailer File contains information about the recording of the magnetic tape and the preprocessing. This file consists of three or more records of 1080 bytes each:
The Null Volume Directory file is the last file recorded on a digital SPOT scene. It consists of only one 360 byte record containing a subset of the information recorded in the Volume Descriptor record of the Volume Directory file. The Null Volume Directory file is followed by three end-of-file (EOF) markers denoting the end of set.
Logical Construction of a Single Volume Scene
FILE RECORD # of RECORDS RECORD
---- ------ ------------ ------
Volume Volume Descriptor 1 360
File Pointer 3 360
Directory Text 1 360
Leader Leader File Descriptor 1 3960
Header 1 3960
Ancillary Ephemeris/Attitude 1 3960
Ancillary Radiometric/Calibration 16 3960
Ancillary Modelisation 1 3960
Ancillary Ground/Reference Controls 1 3960
Ancillary Histogram 4 3960
Ancillary Map Projection 1 3960
Annotation 1 3960
Imagery Imagery File Descriptor 1 3960 or 5400
Image Data n* for PAN 8640
3n* for MULTI 10980
Trailer Trailer File Descriptor 1 1080
Trailer 2 or more 1080
Null Null Volume Descriptor 1 360
(n*) corresponds to the number of lines of image data.