Re: VisAD coordinate systems question

• To: John Emmerling <bayes4@xxxxxxxx>
• Subject: Re: VisAD coordinate systems question
• From: Don Murray <dmurray@xxxxxxxxxxxxxxxx>
• Date: Thu, 24 May 2001 09:19:06 -0600

Hi John-

I'm cc'ing this to the visad-list because I think this is a good example
that others might be interested in.  The approach I'd take is to create
a LogCoordinateSystem, apply it to your range values and map the
reference RealType to the YAxis.  You can see the result at:

ftp://ftp.unidata.ucar.edu/pub/dmurray/LogTest.jpg

and the code at:

ftp://ftp.unidata.ucar.edu/pub/dmurray/LogTest.java

A couple of notes:

1) I had to explicitly set the range for the YAxis ScalarMap, or nothing
would plot.  This appears to be a bug in VisAD which we'll look into
further.

2) LogTest shows some of the new features on how you can set axis labels
using AxisScale.

3) Someday, I hope to incorporate the LogCoordinateSystem in LogTest
into core VisAD.  If anyone out there with fresher math skill than mine
has comments on the logic I used, let me know.  The version in LogTest
will let you specify the log base you want to use.

If you have questions on the methods, let me know.

Don
*************************************************************
Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************

John Emmerling wrote:
> 
> Hi Don,
> 
> Usually everybody gets one question so here's mine.
> 
> Is there a simple way to get VisAD to display intrinsically linear data
> logarithmically?
> 
> For example, you would feed it 4 data points where y as a function of x
> is:
> 
> x           y
> -       -----
> 0          10
> 1         100
> 2        1000
> 3       10000
> 
> etc.
> 
> And the resulting plot would appear as a straight line with tick marks 10,
> 100, 1000, 10000, etc. equally spaced on the y axis?
> 
> I understand there are issues with this but all I need is a general answer
> as to what classes in the VisAD package are involved, etc.
> 
> BTW I am not a mathematician or scientist nor do I play one on TV, but I
> hope you can understand the question regardless.
> 
> Thanks!
> 
> --John Emmerling