Hi Leonard,
Leonard Mada wrote:
> I wish to discuss 3 points:
>
> 1. From the "Scales and Intervals
Specification"
> (http://specs.openoffice.org/chart/Chart_Scales_a
nd_Intervals.odt):
>>
>> 1.
>>
>>
>> Interval frequency
>>
>> *Frequency for major intervals*
>>
>> The frequency of major intervals of a linear scaled
axis is defined as
>> step width (expressed similar the axis
corresponding data) (e.g. 2.0,
>> 7.65 or 1000.0). The number of major intervals over
the axis results
>> from it.
>>
>> The major interval for logarithmic scales behaves
like this: 1 is one
>> order of magnitude. 2 is 2 orders of magnitude etc.
That means log(x2)
>> - log (x1) = major interval, where x1 is one major
tick and x2 is the
>> next one.
>>
>> For example typically you want to have major
tickmarks at 1, 10 ,100,
>> 1000 and so on. You have to set it to 1, because
of: log(100) - log
>> (10) = 1.
>>
>> /Question: Is it useful that values below 1 are
allowed?/
>>
>
> Values below 1 are sometimes useful, too. For very
small variations, one
> may choose 0.5 (and also sometimes a different base for
the logarithm:
> e.g. for some binary data log base 2 is more
appropriate, see also point
> 2 below). A very good example is chemistry: when
working with pH (e.g. a
> titration curve), we may want smaller divisions, like
7.5 .. 8.0 .. 8.5,
> or IF plotting the pI of a mixture of proteins, then
even smaller values
> may be needed (the pI may differ by as little as 0.1,
so even 0.5 may be
> large; see http:/
/en.wikipedia.org/wiki/Isoelectric_point for an
> explanation of the isoelectric point and also this
example for a better
> understanding: http://www.pierroton.inra.fr/genetics/2D/variation.html).
>
> Another useful logarithmic scale is based on dB: e.g.
the audiogram, see
> http://www.sfu.ca/sonic-studio/handbook/Audiogram.html
for an example
> (dB = 20 * log (p2/p1), where p is sound pressure ).
Here, the hearing
> loss is coded as positive dB, BUT the scale is inverse
(it is increasing
> from top to bottom and thus decreasing in the opposite
direction, aka
> top is 0 dB and bottom is 80 dB; the frequency changes
in steps of 2,
> i.e. step of 1 for log base 2, but step less than 1 if
the log is base 10).
>
Thanks for answering this question. I removed it from the
spec and will
leave the implementation as is, allowing intervals smaller
than 1.
For the other two points please submit feature request
issues.
Thanks for your feedback and input,
Ingrid
> 2. Would it be possible to add different bases for the
logarithm. While
> base 10 is more often used (easier visualisation),
sometimes base 2 (or
> ln with base e) are more advisable.
>
> 3. Have option to display original values for
logarithmic scale OR the
> logarithm values: this latter approach is often used
when referring to
> changes of a parameter over its baseline (e.g. by a
factor of 10 = 1 in
> log scale). It also becomes impractical to display the
actual value when
> having a very wide scale, e.g. 1- >10^8 (it is
easier to display 0..8).
> For further examples see also the figures inside the
following articles:
> http://www.nature.com/hdy/journal/v93/n6/pdf/6800559a.p
df and
> http
://www.jneurosci.org/cgi/reprint/25/43/10049 (both are
free).
>
> This article (http://doi.ieeecomputersociety.org/10.1109/TVCG.2006.126
)
> may be also interesting (for other reasons), but I do
not have access to
> it.
>
> I hope this is useful,
>
> Leonard
>
>
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