[R] Postscript query: plotting long vectors

[Don MacQueen]

When I run the example in R 1.6.2, and view it with gs, I get a good plot.
When I run the example in R 1.7.0, and view it with gs, I get a bad plot.
(run on the same host)

My "bad plot" is as described by Stephen.

In the "good" postscript file, about 100 lines in, there is this:
%%EndProlog
%%Page: 1 1
bp
77.04 91.44 743.76 534.96 cl
0.0000 0.0000 0.0000 rgb
0.75 setlinewidth
[] 0 setdash
np
101.73 313.20 m
101.74 313.21 l
101.74 313.23 l
101.74 313.24 l
101.75 313.25 l
(followed by ~200000 lines of the same type, with slowly changing values)

In the "bad" postscript file, at about the same point in the file, is this:
%%EndProlog
%%Page: 1 1
bp
77.04 91.44 743.76 534.96 cl
0 0 0 rgb
0.75 setlinewidth
[] 0 setdash
np
101.73 313.20 m
0.00 0.01 l
0.00 0.01 l
0.00 0.01 l
0.00 0.01 l
0.00 0.01 l
(followed by ~200000 lines, including some like these)

0.00 0.00 l
0.00 0.00 l

0.00 -0.01 l
0.00 -0.01 l

0.00 -0.00 l
0.00 -0.00 l

Looks like it might be a formatting issue on how these lines were written.

My version information:

---- 1.6.2 ----
>  version
platform sparc-sun-solaris2.7
arch     sparc              
os       solaris2.7         
system   sparc, solaris2.7  
status                      
major    1                  
minor    6.2                
year     2003               
month    01                 
day      10                 
language R                  
>

---- 1.7.0 ----
>  version
          _                  
platform sparc-sun-solaris2.7
arch     sparc              
os       solaris2.7         
system   sparc, solaris2.7  
status                      
major    1                  
minor    7.0                
year     2003               
month    04                 
day      16                 
language R                  

[245]% gs --version
5.50

-Don

At 5:59 PM +0100 5/29/03, Stephen Eglen wrote:
>Hi,
>
>I have a query about the maximum length of vector that can be plotted
>in one go in a postscript driver.  Try the following code (in 1.7.0;
>version details below):
>
>t <- seq(from=0, to=4*pi, length=200000)
>y <- sin(t)
>postscript(file="o.ps")
>plot(t, y, type="l")
>dev.off()
>
>If I view the postscript file o.ps in "gv", it takes many seconds
>before eventually the axes appear, but then only one vertical line is
>drawn within the plot area -- there is no sine curve.  (this is on a
>fast dual processor linux machine with 2Gb RAM.)  This is clearly a
>postscript problem, rather than a R problem, since reducing the length
>of t down to something like 2000 solves the problem.  By looking at
>the file o.ps it looks like the line is drawn by one "rlineto" call
>per point, followed eventually by a "stroke" after the last point.
>I'm guessing that the postscript interpreter simply cannot remember so
>many points in the path before it gets to the stroke.
>
>The example above is artificial, but this problem appeared with a real
>data set this morning.  The fix was to replace the single call to
>plot() with many calls to line(), breaking the t and y vectors into
>more manageable chunks; in this way, each postscript path was
>manageable and we got the plot.
>
>I tried plotting the same long vectors in gnuplot by first writing
>them from R:
>
>write.table(cbind(t,y), sep="\t", file="eg.dat", row.names=F, col.names=F,
>             quote=F)
>
>and then in gnuplot:
>
>set term postscript
>set output "gnuplot.ps"
>plot "eg.dat" wi lines
>
>This came out fine; in gnuplot.ps every 400 lines during the plot it
>outputs "currentpoint stroke M" (M is defined to moveto).  I had a
>look at the gnuplot source (gnuplot-3.7.3/term/post.trm) and found
>that it does keep count of the length of the current postscript path:
>e.g. in the function PS_vector(x,y) we see (line 1122):
>
>	if (ps_path_count >= 400) {
>		fprintf(gpoutfile,"currentpoint stroke M\n");
>		ps_path_count = 0;
>	}
>
>so every 400 points it draws the line so far and then continues.
>(Matlab .ps files also seem to have regular "MP stroke".
>
>I had a quick look in the corresponding R code src/main/devPS.c and
>could not see any counter.  Would it be worth adding such a counter
>and periodic line output to PS_Polyline?
>
>
>>  version
>platform i686-pc-linux-gnu
>arch     i686            
>os       linux-gnu       
>system   i686, linux-gnu 
>status                   
>major    1               
>minor    7.0             
>year     2003            
>month    04              
>day      16              
>language R
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-help


-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA