bugGNU Octave - Bugs: bug #58001, All points in plot sent to output...


bug #58001: All points in plot sent to output resulting in very large files

Submitted by:  None
Submitted on:  Mon 16 Mar 2020 05:46:54 PM UTC  
Category:  Plotting Severity:  1 - Wish
Priority:  1 - Later Item Group:  Matlab Compatibility
Status:  Wont Fix Assigned to:  None
Originator Name:  ADAM MAJEWSKI Originator Email:  -email is unavailable-
Open/Closed:  Open Release:  dev
Operating System:  GNU/Linux

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Tue 17 Mar 2020 05:49:52 PM UTC, comment #2: 

This is known Octave behavior.  Whether you want to want to call it a bug or a feature is down to interpretation.  The same behavior is also exhibited onscreen.  The number of points that Matlab passes through their plotting pipeline to OpenGL for rendering is based on the resolution and zoom level of the screen.  Octave takes the easy approach and just plots everything.  The same thing happens for printing (since it is based on the plot).  If you have a lot of points then every one will get sent to the eventual plot.

Many Octave users prefer control over ease of use.  With that frame of mind, it is prefered to filter the number of points in a manner that is most appropriate for your data, rather than relying on an sort of automated algorithm which can't be best for all datasets.

Tentatively marking as "Won't Fix".

Rik <rik5>
Project Administrator
Tue 17 Mar 2020 08:06:51 AM UTC, comment #1: 

The data vector you pass to the plot command has 5 million points. If the resulting file has 78 MB, this means you have about 16 bytes per point: a space, a comma, two decimal points, leaves you 6 significant digits per coordinate. This is very reasonable.

On the other hand, the matlab file (which seems to have only 15.9 kB on my side) has first used the most aggressive white space, comma, and leading zero elimination conceivable (I hadn't known that svg allows that, but it really does) making it quite hard to read and a small nightmare to parse the points back (I really do that sometimes). I don't know if I think that a good idea, but in any case this would give you savings on the order of 25%. No, matlab has also decided that you need only one data point per quarter of a nominal pixel horizontal distance (where your figure is 560 pixels wide) apart from the vertical maxima and minima, and has deleted all points in between. You could have achieved exactly the same result (apart from the whitespace ... elimination mentioned above) by two lines of preprocessing your data:

ind=unique([find(y(2:end-1)>y(3:end)&y(2:end-1)>=y(1:end-2))+1 find(y(2:end-1)<y(3:end)&y(2:end-1)<=y(1:end-2))+1 (1:2500:length(y))]);

gives me a 34.2 kB file. And very probably there are free online out there that you can pass your svg files to and that remove redundant data points, optimally even with a specified tolerance. But I would not want such a thing to happen automatically -- is there an option to turn this off, or is it impossible in matlab to generate an svg file with the exact nodes that you specify?

Michael Leitner <mleitner>
Mon 16 Mar 2020 05:46:54 PM UTC, original submission:  

I have made svg file :

using code:
title("Graph of function sin(exp(x))");
print -dsvg "a.svg"

The size of svg file is 78.0 MB

Using matlab code :

print('-dsvg',strcat('Graph of sin(exp(x)) function','.svg'))

it is 41 KB large




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    Follow 5 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2020-03-17 rik5 Severity3 - Normal => 1 - Wish
        Priority5 - Normal => 1 - Later
        StatusNone => Wont Fix
        Release4.2.2 => dev
        Summaryto big size of svg => All points in plot sent to output resulting in very large files

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