[Bug 1200632] Re: X axis is shifted to the right when you zoom in

[Lance Arsenault]

quickplot reads values in as doubles which can only store so many digits
in the mantissa.  So when quickplot reads in all your time values it may
be losing digits that are needed at the end of the mantissa.   So, for
example (not actual), it reads 1559245834.00 as 155924583.0e+1 loosing
the 4.  Having quickplot be able to handle more digits would slow down
quickpplot, and require more coding at this point.  I think you might
try subtracting  1559245764  from all your time values, and plot that.
I'm pretty sure that will work.  I'm guessing that's the time in seconds
since the year 1970, https://en.wikipedia.org/wiki/Unix_time.  Most of
the "time" you need to subtract an offset to use it in floating point
calculations.

1559245834 seconds  ---  Looks like you got this data about 117 days
ago.

When you "zoom-in too far" with quickplot you are starting to round-off
the floating point values to much in the zoom calculations, and the
values being displayed will be just the artifacts from the round-off
process, and not what you want to look at.  Adding higher zooming-
precision means adding higher floating point calculation precision.


A feature request might be to add code that detects when a the variance in a 
field is much smaller than the fields mean value, and have quickplot 
automatically subtract an offset to the stored values; but display number 
values as they originally were.   I've though about doing that in the past, but 
as it turns out quickplot is not the only program that will have problems 
handling like fields, and in all my use cases I filtered these "problem fields" 
out before using them with any program.

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Title:
  X axis is shifted to the right when you zoom in

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[Bug 1200632] Re: X axis is shifted to the right when you zoom in

[Lance Arsenault]

Hi,

I'm the sole upstream developer of quickplot.  Lance.


I'd like to fix this bug, but I'm having trouble understanding what the bug is, 
and how to see it.

The way I see it, quickplot does not draw any axises.  Quickplot draws a
grid of x and y lines.   Grid lines are labeled at even intervals.
When you drag the graph (with the left mouse button pressed move the
pointer) you can see grid labels spaced at a little less than the
distance of the current veiw port size.  These grid labels are
recalculated for every zoom level, so they "jump" around a lot when you
zoom.  The label positions are regular, but not super nice every time.
It's kind of like the regular latitude and latitude labels on a paper
map.  It's just a regular periodic pattern.  The labels may end up in a
stupid location, but it is not supposed to be giving wrong information.

An easy way to plot your test data is with this one-liner:

   echo -e "1 1\n2 2\n 3 3\n 4 4" | quickplot -

Can you show me a snapshot as a png file of this bug behavior?   Or did
I just resolve this bug by explaining what you are seeing?  Or can this
evolve into a Quickplot feature request (granted I don't understand it)?

--lance

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Title:
  X axis is shifted to the right when you zoom in

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