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+Project pst-geo-compress 2009-07-30
+========================
+
+Author: Heiko Oberdiek <oberdiek@uni-freiburg.de>
+License is LPPL 1.3c,
+ maintainance status: maintained
+ current maintainer: author
+
+Files:
+ README (this file)
+ pst-geo-compress.pl
+ pst-geo-decompress.pl
+
+Requirements: Ghostscript >= 8.56 (if prediction is used)
+
+`pst-geo' (CTAN:graphics/pstricks/contrib/pst-geo/) comes with
+huge data files:
+ CTAN:graphics/pstricks/contrib/pst-geo/data/data.tgz
+ CTAN:graphics/pstricks/contrib/pst-geo/dataII/dataII.tgz
+Unpacked the data files consume about 134 MB.
+
+The data files (files with extension `.dat') are PostScript files.
+PostScript supports compression and decompression via filter.
+The Perl script `pst-geo-compress.pl' compresses the data files
+using the /FlateEncode filter and adds code to decompresses the file,
+if read by a PostScript interpreter. Now the space requirements of
+the data files is about 24 MB.
+
+Caveat: Filters /FlateEncode and /FlateDecode require
+PostScript language level 3 (supported by ghostscript).
+(LZW compression don't need language level 3, but
+the compression is less effective.)
+
+Size reduction details:
+* Much unnecessary white space is removed.
+* Some comments are removed (especially number comments
+ in .dat files of data.tgz), the remaining comments are preserved
+ (especially city names).
+* /FlateEncode filter.
+* PNG prediction (method `up') is used for most of the files.
+ Spaces at line ends are added to fill the space up to
+ to the columns count. This improves the prediction,
+ because these files contains long lists of sorted coordinate pairs.
+ The prediction columns count is also the maximal line length,
+ because of a ghostscript bug:
+
+Ghostscript has a bug regarding prediction, it is fixed in
+version 8.56 (2007-03-14):
+
+| 2006-12-11T17:30:53.980862Z L. Peter Deutsch
+|
+| Fixes bug: the PNG predictor filters produced incorrect data for the last
+| pixel of each row. (The encoder and decoder had matching bugs, so
+| encode+decode produced the correct result!) Fixes a diff in PS3 CET
+| 23-12U-1.
+
+By having each line at the same length, the last byte of a row
+has always the same value (end of line character). This does
+not trigger this bug (tested with gs 7.07/8.64).
+
+After compression the files aren't human-readable any more.
+The Perl script `pst-geo-decompress.pl' can be used to
+decompress a data file.
+
+Both scripts know option -h that prints a short usage screen.
+Option --gscmd allows to configure the ghostscript programm call,
+if the automatic ghostscript isn't sufficient.
+
+`pst-geo-compress.pl' is called inside the directory where
+the data files are present. Options `-1' and `-2' choose
+between the files from `data.tgz' and `dataII.tgz'.
+
+`pst-geo-decompress.pl' expects the data file to decompress.
+If an output file is given, the result is stored there. Otherwise
+standard output is used.
+
+History:
+ 2009-07-30 v1.0 First release
+ 2009-07-30 v1.1:
+ * Workaround for ghostscript bug added:
+ * Files that are compressed with prediction have
+ equal line length.
+ * Removing comments (except for city data files)
+ * Obsolete option --prediction is therefore removed
+ * Adding standalone test mode (option `--test').
+