Hello Yeti,
Thanks for the response. I understand what you are saying and I think this is
the problem - it could be my outliers that are causing my issues. As an
example, for the type data files in question, the ASCII file gives _all_ data
points to a precision of six decimal places (e.g., the maximum value might be
7.335011 and the minimum might be -5.429196 but most of the data are values
like -0.010911).
For example, here are the "Copy table to clipboard" results for one of the
images I am having trouble with:
Statistical Quantities
File: C:\Users\gwclark\Documents\GWC\Research\SPM
Research\Spr14\SPM Data GWC
JanSpr2014\052314.DIR\052314111830_0.SIG_NC_PHASE_BKW.binprocessedc2.txt
Selected area: 249 × 256 at (0, 0) px
19.45 × 20.00 at (0.00, 0.00) µm
Mask in use: No
Average value: -0.02
Minimum: -5.43
Maximum: 7.34
Median: -0.02
Ra: 0.02
Rms: 0.09
Rms (grain-wise): 0.09
Skew: -6.98
Kurtosis: 2.51e+003
Surface area: N.A.
Projected area: 389.062 µm^2
Inclination θ: N.A.
Inclination φ: N.A.
The above is for the entire image. If I make a mask that excludes the outliers
and includes a relatively constant region, I get data like this:
Statistical Quantities
File: C:\Users\gwclark\Documents\GWC\Research\SPM
Research\Spr14\SPM Data GWC
JanSpr2014\052314.DIR\052314111830_0.SIG_NC_PHASE_BKW.binprocessedc2.txt
Selected area: 92 × 212 at (40, 51) px
7.19 × 16.56 at (3.20, 4.00) µm
Mask in use: No
Average value: 0.00
Minimum: -0.14
Maximum: 0.07
Median: 0.00
Ra: 0.01
Rms: 0.02
Rms (grain-wise): 0.02
Skew: -0.756
Kurtosis: 4.8
Surface area: N.A.
Projected area: 52.405 µm^2
Inclination θ: N.A.
Inclination φ: N.A.\
Here, neither the max nor the min is to four (or even three) digits. So, when
using the mask it appears that the min/max values for the entire image are
still influencing the calculation, correct?
Thanks,
GWClark
-----Original Message-----
From: David Nečas (Yeti) [mailto:[email protected]]
Sent: Friday, June 06, 2014 2:30 PM
To: Gwyddion use discussion
Subject: Re: [Gwyddion-users] "Statistical Quantities" in Gwyddion 2.36
On Fri, Jun 06, 2014 at 04:00:59PM +0000, Clark, Gregory W. wrote:
> Everything works fine EXCEPT that when I use the "Statistical
> Quantities" and look at the data in the window under "Parameters" the
> precision of the quantities is often too small. Sometimes I get four
> decimal places on all the Parameters, but sometimes I only get only
> two decimal places. The quantities I'm working with are small (mV)
> surface potentials.
The absolute scale does not matter, the format is chosen automatically
according to the magnitude of the values. You should always get at least three
digits, often four. Generally, if the value range is close to a power of 10
but smaller (e.g. 0.9) you will get 3 digits, otherwise 4. So the ratio
between difference of 1 in the last digit and the value range is kept about
1/1000.
If the range is [0.0437, 10.5106] the minimum and maximum are shown as
0.04 and 10.51, i.e. the precision is absolute. Is this the problem?
Do your small values have much better absolute precision than large values?
Rms and Ra are displayed with the same format. Here an additional digit might
be useful occasionally as they are typically several times smaller than the
value range. Is this the problem??
Regards,
Yeti
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"Graph Databases" is the definitive new guide to graph databases and their
applications. Written by three acclaimed leaders in the field,
this first edition is now available. Download your free book today!
http://p.sf.net/sfu/NeoTech
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