Parent Topic: Supported File Formats
PCIDSK (PIX)
PCIDSK is fully supported by the GeoGateway library. It is the only
file format
which currently allows ``adding'' segments, and one of the few which allows
data description fields to be extracted and saved to the file.
A variety of database maintenance operations for PCIDSK files can be
performed
from the Works File Utility, often found as the ``Utility...'' entry in
the File menu of PCI applications. A complete format specification for
the PCIDSK format can be found in the PCIDSK Database Reference Manual
distributed with EASI/PACE.
Export of PCIDSK files is supported. These files are exported with
a type of "PIX".
The generated file will (as usual) have all images channels of
the same type which will be the ``largest'' of the input image
data types. Also, bitmap, vector, lut and pct segments will
be created as required. Georeferencing is transferred.
The following options strings can be provided to control the raster format
of the resulting file.
- "BAND": This produces a band interleaved file. This format is the default.
- "PIXEL": This produces a pixel interleaved file.
- "FILE": This produces a PCIDSK file (header), plus a separate external
file for each raster channel.
- "TILED[nnn] [compression] [ENCRYPT=key]": This produces a tiled file.
If the TILED keyword is followed by a number, then this will set the
tile size, otherwise a tile size of 127x127 is selected. Normally the
tiles are stored uncompressed, but if the JPEG, or RLE keyword is added
(separated by a space), then the tiles will either be JPEG (lossy)
compressed, or run length encoded. Example values would be "TILED",
"TILED512 JPEG", and "TILED RLE". If the ENCRYPT=key option is added,
the image data for the file will be kept in encrypted form, based on the
key given. This key will have to be supplied when the file is used in
the future to unencrypt the data. An example would be
"TILED RLE ENCRYPT=password".
The choice of layout is primarily based on performance. BAND
interleaved stores all the data for one band together, and
gives superior performance when not all bands are
being accessed at all times. PIXEL interleaved stores data the
data for all bands at a particular pixel together, and may give
somewhat improved
performance when all bands are being utilized at once. FILE
interleaved is similar to BAND interleaved, but the image channel
data is stored in external files (one file per band).
Tiled files have the image organized in many square subimages, and
can be much faster to access when only a subarea is being extracted,
such as in file viewing. Tiling is also the only format which
supports compression formats, with the default being no compression.
JPEG compression is a lossy compression, and is normally suitable for
continuous images such as airphotos. RLE (Run Length Encoding)
compression is lossless, but will only give good compression for
images where long sequences of pixels have the same value, as typically
happens in pseudo-coloured, or thematic images.
The PCIDSK file format is described in detail in the ``PCIDSK Database
Reference'' manual. This is typically called dbref.ps on the PCI
documentation CD, and may be available on the PCI ftp site at
ftp://ftp.pci.on.ca/pub/doc_v60/prog/dbref.ps.Z, or a similar location.
See Also: File Browser, CIM, PCIMOD, III
Parent Topic: Supported File Formats
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