       Re: Coloring function

• To: mathgroup at smc.vnet.net
• Subject: [mg121478] Re: Coloring function
• From: Heike Gramberg <heike.gramberg at gmail.com>
• Date: Fri, 16 Sep 2011 05:49:47 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201109150837.EAA29104@smc.vnet.net>

```It probably helps to specify ColorFunctionScaling->False. With ColorFunctionScaling->True (which is the default setting)
the arguments of the ColorFunction are scaled to lie between 0 and 1. When ColorFunctionScaling is False, the actual values of
x, y, and z are used. Note that since RGBColor expects its arguments to be between 0 and 1, you would then need to rescale
Abs[x] or x^2+y^2 in your examples by hand. So for your examples you would get

ListPointPlot3D[
Flatten[Table[{i, j, 0}, {i, -30, 30}, {j, -30, 30}], 1],
ColorFunctionScaling -> False,
ColorFunction -> Function[{x, y, z}, RGBColor[Abs[x]/30, 0, 0]]]

and

ListPointPlot3D[
Flatten[Table[{i, j, 0}, {i, -30, 30}, {j, -30, 30}], 1],
ColorFunctionScaling -> False,
ColorFunction ->
Function[{x, y, z}, RGBColor[(x^2 + y^2)/(30^2 + 30^2), 0, 0]]]

Heike.

On 15 Sep 2011, at 10:37, guiwi wrote:

> Hi everybody. I have a general problem with the coloring method of
> ColofFunction. Let's consider a plane of points that one wants to plot
> with ListPointPlot3D. If I want to color the points according to their
> x position, I write:
>
> ListPointPlot3D[Flatten[Table[Table[{i, j, 0}, {j, -30, 30}], {i, -30,
> 30}], 1], ColorFunction -> Function[{x, y, z}, RGBColor[x, 0, 0]]]
>
> and that indeed works. But if I want to color according to the
> absolute value of x and use
>
> ColorFunction -> Function[{x, y, z}, RGBColor[Abs[x], 0, 0]]
>
> the coloring is not symmetrical around the x=0 position, but
> identical to the previous case. Another problem is to obtain a radial
> coloring with
>
> ColorFunction -> Function[{x, y, z}, RGBColor[x^2+y^2, 0, 0]]
>
> where the origin of the radial coloring is not at {0,0} but somewhere
> on the edge of the plot. Anyone knows how to control that coloring ?
> Thanks.
> Guillaume
>

```

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