SIOSEIS plot file format

	The SIOSEIS process plot parameter OPATH creates a file very similar 
to the Versatec and other raster plotters.  A raster is the same as a dot and
is represented as a bit in the plot file, where a 1 turns the raster on.
	A raster file is the same as a bitmap.
	Historically, the Versatec was an electrostatic plotter.  In 2011, the
only electrostatic plotters are made by Atlantek (now Printex.com) and iSys.
The mechanical point creating the dot is called a NIB.  The nib is charged when
the bit is set on.  On most plotters, there are 300 nibs in an inch, and the
width of the paper contains thousands of nibs on a "head".  All nibs can be 
charged at the same time.  After a full raster line is received from the special
paper advances one nib, without a "line feed".  
	The HP DesignJet plotters are raster plotters, but there is only one
print head or print cartidge for each color.  A drop of ink is placed on the paper.
This is why the DesignJet is slower than an electrostatic plotter.  The DesignJets
also require a line feed in order to advance the paper.
	
	The old Versatecs used a special liquid bath to attach the special ink to
the charge.  EPC plotters are were not raster plotters, but were electrostatic
and burned the paper slightly to leave a mark.  A larger charge left a darker spot.

	The SIOSEIS plot file consists of a 3520 byte ASCII header followed by a
continuous string of rasters.  All sioseis plot related programs (sio2hp, versatec,
sio2sun) read and write according to the number of bits or bytes in a raster line
for each particular raster plotter.  Sioseis differentiates plotter models according 
parameter NIBS or PLOTTER, which then uses a table for the number of bytes in each
raster line.  Thus, what sioseis calls the Atlantek 7224 has 4608 nibs or 576 bytes
in a line (200 nibs per inch and 23.04 inches wide) and the Atlantek 7225 has 4704
nibs or 588 bytes (200 nibs per inch and 23.52 inched wide).

	The 3520 ASCII header bytes are 44 "card images", each card having 80 ASCII
characters.  The first card had the date the file was created.  Card images 2-43
are the SEGY tape header.  Cards 42-44 contain sioseis plot parameters including
the NIBS parameter.
	ASCII line 43, column 67-70 contains parameter NIBS or PLOTTER.
	ASCII line 43, column 71-74 contains the number of "live" rasters in each line
(the number of rasters actually used in the seismic plot).  Needed by Sun raster files.
	ASCII line 43, column 75-80 contains the number of raster lines in the file.
(the number of lines in the file is valid only if the plot file is closed by sioseis)

	See source code programs sio2sun.c, sioplt.c, sio2hp.f, versatec.f for examples.
	FYI, Plotters and terminals have different coordinates systems.  Plotters have
the (0,0) original at the top left and CRTs at the top right.

Example
57>more plt
sioseis << eof
procs syn filter plot end
syn
   ntrcs 30 secs 2 tva .1 1500 1 end
end
filter
   pass 20 80 end
end
plot
   nibs 7225 ann sh&tr taginc 2
   opath pltfil.sio srpath pltfil.ras end
end
end
eof
display -rotate 90 pltfil.ras
convert -rotate 90 pltfil.ras pltfil.png

pltfil.png

         1         2         3         4         5         6         7         8
12345678901234567890123456789012345678901234567890123456789012345678901234567890
Card image 1:
 SIOSEIS ver 2011.2.5 (28 Feb. 2011)Mon Mar 21 11:09:56 2011      7225  45   901

Card images 42-44:
 vscale=   2.50 trpin =  20. def = 0.10 scalar =  -1.0000     hscale =    0.0   
   501 samples with a delay of 0.000 secs. Sample interval = .004000 secs.      
 Plot times:  0.0000 to  0.0000 Label SH&TR  Header date    0 JAN.  0  0: 0     

Sun rasterfile format (rasterfile.h)
/*  /usr/include/rasterfile.h  */
#define   RAS_MAGIC 0x59a66a95
#define RT_OLD      0    /* Raw pixrect image in 68000 byte order */
#define RT_STANDARD 1    /* Raw pixrect image in 68000 byte order */
#define RT_BYTE_ENCODED  2    /* Run-length compression of bytes */
#define RT_FORMAT_RGB    3    /* XRGB or RGB instead of XBGR or BGR */
#define RT_FORMAT_TIFF   4    /* tiff <-> standard rasterfile */
#define RT_FORMAT_IFF    5    /* iff (TAAC format) <-> standard rasterfile */
#define RT_EXPERIMENTAL 0xffff     /* Reserved for testing */
     /* Sun registered ras_maptype's */
#define RMT_RAW          2
     /* Sun supported ras_maptype's */
#define RMT_NONE    0    /* ras_maplength is expected to be 0 */
#define RMT_EQUAL_RGB    1    /* red[ras_maplength/3],green[],blue[] */

        struct rasterfile {
                int32_t  ras_magic;
                int32_t  ras_width;
                int32_t  ras_height;
                int32_t  ras_depth;
                int32_t  ras_length;
                int32_t  ras_type;
                int32_t  ras_maptype;
                int32_t  ras_maplength;
        };