Re: XYcolor plots

[Jean Bréfort <jean brefort free fr>]

Hi John,

Actually, you can choose the colors: select the Z axis, then the color
scale page and click New or Duplicate. You can build your own custom
color scale.

Hope this helps,
Jean

Le samedi 13 novembre 2021 à 08:31 -0700, John Denker via gnumeric-list
a écrit :
> Hi Folks --
>
> The Colored XY plot feature has the potential to be extremely
> useful. I can give you a long list of important use-cases
> if you want (see e.g. below).
>
> Right now it is marginally useful. The main drawback is lack
> of control of the Z axis, i.e. the color. Different Z values
> result in different colors, but the mapping from Z value to
> color is undocumented and inscrutable.
>
> The documentation for Colored XY plots, in its entirety, says:
>
> > 10.3.4.  Colored XY Plots
> >
> > Work in Progress
>
> Reference:
>   
> https://help.gnome.org/users/gnumeric/stable/sect-graphs-overview-types.html.en#sect-graphs-overview-types-coloredxy
>
> Suggestion: It would be great if the Z axis would accept *strings*
> like this:
>       "#00ff00"               simplest case: solid green
>       "#00ff0040"             green at 25% opacity
>       "#ff0000,#0000ff"       red outline, blue fill
>
> Users who want to plot numerical data can construct their own
> colormap consisting of an array of strings, then apply the
> offset() function.
>
> Once the dust settles, it would be nice to document the
> Colored XY plot feature.
>
> ============================
> Here is one use-case among many:
>
> Suppose we have a QAM64 modem. There are 64 possible codes
> that could be sent, each with an X,Y value. At the receiver
> we would like to plot the data. The X,Y position is given
> by the voltages as received (including noise), and the color
> is determined by what the symbol was /supposed/ to be. That
> way we can see where the category boundaries are. We can
> see to what extent a given symbol is encroaching on another
> category.
>
> It would be unsatisfactory to implement this as 64 separate
> XY plots for multiple reasons. First, that would be grossly
> laborious. What's worse, if the red plot is in front, that
> would put *all* the red points in front, which is not what
> we want. Instead, we want the Z-order to be determined by
> the order in which the symbols were received.
>
> ===============================
> Additional remarks:
>
> *) Do not let the perfect be the enemy of the good. I can
> happily live without the following creeping features.
>
> *) Creeping feature:
>
>  "#ff0000,#0000ff,3,5.5"  red outline, blue fill, shape 3, size 5.5
>
> This would allow the marker shape (circle, square, diamond,
> ...) to be determined on the fly, and also the marker size.
>
> This would allow a Colored XY plot to do everything a Bubble
> plot does, and more.
>
> *) I'm not sure, but I wonder whether it might be better to
> put the information in 4 columns rather than in a single Z
> column. That is, separate columns for outline color, fill
> color, marker shape, and marker size. Hmmmm.
>
> *) Creeping feature:
>
> As for the lines, as opposed to the symbols: Let the line
> segment from point 1 to point 2 be a linear gradient, sweeping
> from the point-1 color to the point-2 color. Anybody who wants
> uniform-color segments can plot two points at each X,Y location
> (ending-point and re-starting-point).
>
> *) Creeping feature:
>
> One could imagine other strings, perhaps X11 color names
> such as DarkGoldenrod4, or perhaps SVG color names (which
> are inconsistent with the X11 names) ... but for my purposes 
> names would be less useful than hex strings. I can compute
> the hex strings as a function of the data using dec2hex(),
> but I can't compute the names.
>
> I suppose the names are harmless, and they will appeal to
> casual users (as opposed to power users). However, they
> are neither necessary nor sufficient. They are not a viable
> substitute for the hex strings.
>
> =========================================
>
> So, how hard would it be to implement color-strings?
>
> Does anybody have any better ideas along these lines?
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