plplot-general

[Plplot-general] color key on shade plots

[Doug H. <dh...@uc...>]

Hi all:  Is there any provision in PLplot for generating a color key to
associate values with colors in cmap1?  This would be the equivalent of
the pgwedge command in PGPLOT.

I am generating a web plot with points that are colored according to
their value, but I need to show the users a color key.

Any ideas would be appreciated!

Regards, 

  Doug Hunt

-- 
dh...@uc...
Software Engineer III, Sometimes Sysadmin
UCAR - COSMIC, Tel. (303) 497-2611

Re: [Plplot-general] color key on shade plots

[Maurice L. <mj...@ga...>]

Doug Hunt writes:
 > Hi all:  Is there any provision in PLplot for generating a color key to
 > associate values with colors in cmap1?  This would be the equivalent of
 > the pgwedge command in PGPLOT.

A value <-> color association in PLplot is called a control point.  Between
these the HLS values are linearly interpolated according to position (value).
So the minimum number of control points is two, at the cmap1 boundaries, but
by increasing the number of control points (through the API, or you can edit a
palette file and load it with the Tk interface) you can get a variety of
effects.  E.g. in the last release I increased the number of control points in
the default map from 4 to 6 to better show off weaker features than the
previous palette.  The maximum number of control points is 256, which should
be far more than anyone really needs.

-- 
Maurice LeBrun    mj...@ga...

Re: [Plplot-general] color key on shade plots

[Doug H. <dh...@uc...>]

Maurice:  Actually, I meant how does one draw a color key on a plot? 
(See the attached graphic).  I can now generate this plot using my
nascent 
PDL interface to PLplot.  The trick that initially stymied me involved
resetting the viewport and window on the same subpage.

I also have a perl module that uses PLplot to interface to the GMT map
database to draw coastlines and political boundaries.

I'll release these to CPAN soon.

Regards, 

  Doug Hunt


Maurice LeBrun wrote:
> 
> Doug Hunt writes:
>  > Hi all:  Is there any provision in PLplot for generating a color key to
>  > associate values with colors in cmap1?  This would be the equivalent of
>  > the pgwedge command in PGPLOT.
> 
> A value <-> color association in PLplot is called a control point.  Between
> these the HLS values are linearly interpolated according to position (value).
> So the minimum number of control points is two, at the cmap1 boundaries, but
> by increasing the number of control points (through the API, or you can edit a
> palette file and load it with the Tk interface) you can get a variety of
> effects.  E.g. in the last release I increased the number of control points in
> the default map from 4 to 6 to better show off weaker features than the
> previous palette.  The maximum number of control points is 256, which should
> be far more than anyone really needs.
> 
> --
> Maurice LeBrun    mj...@ga...

-- 
dh...@uc...
Software Engineer III, Sometimes Sysadmin
UCAR - COSMIC, Tel. (303) 497-2611

Re: [Plplot-general] color key on shade plots

[Alan W. I. <ir...@be...>]

Nice plot, Doug!

I will have to learn how to do that from Python....;-)

Alan

email: ir...@be...
phone: 250-727-2902	FAX: 250-721-7715
snail-mail:
Dr. Alan W. Irwin
Department of Physics and Astronomy,
University of Victoria, P.O. Box 3055,
Victoria, British Columbia, Canada, V8W 3P6
__________________________

Linux-powered astrophysics
__________________________

On Wed, 13 Feb 2002, Doug Hunt wrote:

> Maurice:  Actually, I meant how does one draw a color key on a plot?
> (See the attached graphic).  I can now generate this plot using my
> nascent
> PDL interface to PLplot.  The trick that initially stymied me involved
> resetting the viewport and window on the same subpage.
>
> I also have a perl module that uses PLplot to interface to the GMT map
> database to draw coastlines and political boundaries.
>
> I'll release these to CPAN soon.
>
> Regards,
>
>   Doug Hunt
>
>

Re: [Plplot-general] color key on shade plots

[Maurice L. <mj...@ga...>]

Doug Hunt writes:
 > Maurice:  Actually, I meant how does one draw a color key on a plot? 
 > (See the attached graphic).  I can now generate this plot using my
 > nascent 
 > PDL interface to PLplot.  The trick that initially stymied me involved
 > resetting the viewport and window on the same subpage.

I see, I didn't understand what you meant by a color key (I usually call it a
"legend"), make sense now.  I agree they're very useful to have, but right
now its basically roll-your-own.  There should probably be an API call to
generate one but you'd still have to set the viewport yourself.

-- 
Maurice LeBrun    mj...@ga...