bugGNU Octave - Bugs: bug #56426, Line plot inaccurate

 
 

bug #56426: Line plot inaccurate

Submitter:  None
Submitted:  Sat 01 Jun 2019 07:30:45 PM UTC
   
 
Category:  Plotting Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Inaccurate Result
Status:  Duplicate Assigned to:  None
Originator Name:  Roland Exler Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 5.1.0
Operating System:  * Any Fixed Release:  None
Planned Release:  None
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Mon 03 Jun 2019 05:37:47 AM UTC, comment #4: 

Thanks for your quick replies. At the moment I'm offset all my data by 2000 years, so I still can use two digit date marks yy/mm/dd as x axis ticks.

Anonymous
Mon 03 Jun 2019 12:21:27 AM UTC, comment #3: 

This is because markers positions (including dots) are computed "by hand" in double precision arithmetic while we rely on opengl transforms for displaying lines.

Pantxo Diribarne <pantxo>
Group Member
Sun 02 Jun 2019 06:11:11 PM UTC, comment #2: 

What I'm still wondering about is the fact the same data plotted with dots instead of lines gives correct result.

Furthermore I'm wondering why interpolation of lines is not done in display coordinates. This would result in correct lines being plotted as the data points are converted correctly to display posiitons in the plot.

Anonymous
Sun 02 Jun 2019 12:50:29 PM UTC, comment #1: 

Thanks for your report. This is a known issue, due to the fact that opengl renderers (Qt and fltk) use single precision arithmetics, see bug #32980 and bug #46168. The workaround is to use gnuplot or substract large offsets from your data before plotting.

Closing report as duplicate.

Pantxo Diribarne <pantxo>
Group Member
Sat 01 Jun 2019 07:30:45 PM UTC, original submission:  

Plotting xy data with large offset of x data values compared to the range to display results in incorrect lines being plotted, while plotting the same data with dots only is correct.

A short example program is attached.

Anonymous

 

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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2019-06-02 pantxo StatusNone Duplicate
        Open/ClosedOpen Closed
        Operating SystemMicrosoft Windows Any

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