On 2017-05-28 10:35-0000 l1q1d wrote:
---
** [support-requests:#43] Colormap log**
**Status:** open
**Group:**
**Created:** Sun May 28, 2017 10:35 AM UTC by l1q1d
**Last Updated:** Sun May 28, 2017 10:35 AM UTC
**Owner:** nobody
Hi, do you have any idea how to have log color in colormap/plshade/colorbar?
I have CC'd my response to your support request to the plplot-general
mailing list. Since that is our preferred support mechanism (to
collect support requests and the discussion of them all in one place),
I ask that you subscribe to that mailing list (see directions at
<https://lists.sourceforge.net/lists/listinfo/plplot-general>) and
follow up there with your (likely inevitable) supplementary PLplot
questions rather than on this deprecated support request tracker.
That is an interesting question concerning color map 1 (N.B. not color map
0 since that is for discontinuous colors). The independent variable of
cmap1 ranges from 0 to 1 (inclusive). We have no switch to interpret
cmap1 values as logs, but that is not necessary since you
can do that conversion yourself. For example, suppose you have an
array z of 3rd coordinates which you would like to represent as a cmap1
color. Then try this transform:
c = log(z/zmax)/log(zmax/zmin) + 1
That c array is proportional to log z as you require, but due to
the linear transformation all values of that array are in the correct cmap1
range from
0 to 1 as you can see by substituting z=zmax where c = 1 and z=zmin
where c = 0 on the RHS.
So use that transformed c array or value anywhere (e.g., plshade,
plshades, plcol1, plcolorbar) that a cmap1 color map value can be
used, and you should be OK. However, as far as I know nobody has ever
tried this so I would appreciate you following up (on the
plplot-general mailing list) with your results (whether good or bad)
for the benefit of both our developers and ordinary users.
Alan
__________________________
Alan W. Irwin
Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).
Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
__________________________
Linux-powered Science
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